Genetics

of

human

hydrocephalus

Human

hydrocephalus

is

a

common

medical

condition

that

is

characterized

by

abnormalities

in

the

flow

or

resorption

of

cerebrospinal

fluid

-LRB-

CSF

-RRB-

resulting

in

ventricular

dilatation

Human

hydrocephalus

can

be

classified

into

two

clinical

forms

congenital

and

acquired

Hydrocephalus

is

one

of

the

complex

and

multifactorial

neurological

disorders

Introduction

Human

hydrocephalus

is

a

significant

medical

condition

with

an

estimated

incidence

of

in

births

-LSB-

-RSB-

Hydrocephalus

is

characterized

by

abnormalities

in

the

flow

or

resorption

of

cerebrospinal

fluid

-LRB-

CSF

-RRB-

resulting

in

ventricular

dilatation

However

hydrocephalus

is

far

more

complicated

than

a

simple

disorder

of

CSF

circulation

-LSB-

-RSB-

Although

commonly

considered

a

single

disorder

human

hydrocephalus

is

a

collection

of

a

heterogeneous

complex

and

multifactorial

disorders

-LSB-

-RSB-

Genetic

factors

are

involved

in

the

pathogenesis

of

hydrocephalus

-LSB-

-RSB-

For

the

purposes

of

this

review

we

categorize

hydrocephalus

as

congenital

which

is

present

at

birth

and

often

associated

with

developmental

defects

and

acquired

which

occurs

after

development

of

the

brain

and

ventricles

-LSB-

-RSB-

The

development

and

progression

of

congenital

hydrocephalus

is

a

dynamic

process

that

is

not

yet

well

understood

It

is

thought

that

it

may

develop

at

an

important

and

specific

embryonic

time

period

of

neural

stem

cell

proliferation

and

differentiation

in

the

brain

-LSB-

-RSB-

Congenital

hydrocephalus

may

occur

alone

-LRB-

non-syndromic

-RRB-

or

as

part

of

a

syndrome

with

other

anomalies

-LRB-

syndromic

-RRB-

-LSB-

-RSB-

In

syndromic

forms

it

is

hard

to

define

the

defective

gene

because

of

the

association

with

other

anomalies

We

will

mainly

focus

on

isolated

forms

of

hydrocephalus

In

genetic

terms

the

isolated

-LRB-

non-syndromic

-RRB-

form

of

hydrocephalus

is

a

primary

and

major

phenotype

caused

by

a

specific

faulty

gene

It

is

estimated

that

about

of

hydrocephalus

cases

have

a

possible

genetic

etiology

-LSB-

-RSB-

In

humans

X-linked

hydrocephalus

-LRB-

OMIM

-RRB-

comprises

approximately

of

the

congenital

cases

with

a

genetic

cause

-LSB-

-RSB-

Although

there

is

strong

evidence

for

genetic

causes

only

one

hydrocephalus

gene

-LRB-

X-linked

-RRB-

has

been

identified

in

humans

Besides

genetic

factors

many

other

factors

influence

the

development

of

congenital

hydrocephalus

such

as

congenital

malformations

intracerebral

hemorrhage

maternal

alcohol

use

-LSB-

-RSB-

infection

-LSB-

-RSB-

and

X-ray

radiation

during

pregnancy

-LSB-

-RSB-

Genetics

in

hydrocephalus

Congenital

hydrocephalus

is

the

more

common

of

the

two

forms

of

hydrocephalus

and

is

probably

the

consequence

of

abnormal

brain

development

and

perturbed

cellular

function

which

emphasizes

the

important

roles

that

congenital

hydrocephalus

genes

play

during

brain

development

In

general

the

recurrence

risk

for

congenital

hydrocephalus

excluding

X-linked

hydrocephalus

is

low

Empiric

risk

rates

range

from

to

-LSB-

-RSB-

indicating

the

rarity

of

autosomal

recessive

congenital

hydrocephalus

-LSB-

-RSB-

However

multiple

human

kindreds

with

congenital

hydrocephalus

have

been

reported

-LSB-

-RSB-

The

loci

or

genes

for

human

autosomal

recessive

congenital

hydrocephalus

have

not

yet

been

identified

but

there

is

at

least

one

locus

for

this

trait

Furthermore

like

animal

models

since

there

is

heterogeneity

among

clinical

phenotypes

there

may

be

more

genetic

loci

in

human

autosomal

recessive

congenital

hydrocephalus

One

kindred

was

reported

in

which

congenital

hydrocephalus

was

transmitted

in

an

autosomal

dominant

fashion

This

condition

was

associated

with

aqueductal

stenosis

but

was

not

associated

with

mental

retardation

or

pyramidal

tract

dysfunction

The

lack

of

mental

retardation

and

pyramidal

tract

dysfunction

was

in

contrast

to

X-linked

or

recessive

congenital

hydrocephalus

with

stenosis

of

the

aqueduct

of

Sylvius

-LRB-

HSAS

-RRB-

in

which

these

abnormalities

are

commonly

seen

-LSB-

-RSB-

Another

study

identified

a

kindred

with

a

microdeletion

of

which

subsequently

developed

hydrocephalus

This

trait

was

also

transmitted

in

an

autosomal

dominant

fashion

-LSB-

-RSB-

Molecular

genetic

studies

have

revealed

that

the

responsible

gene

for

X-linked

human

congenital

hydrocephalus

is

at

encoding

for

-LRB-

protein

-RRB-

-LSB-

-RSB-

The

mutations

are

distributed

over

the

functional

protein

domains

The

exact

mechanisms

by

which

these

mutations

cause

a

loss

of

protein

function

are

still

under

investigation

Another

form

of

this

disorder

acquired

or

adult-onset

hydrocephalus

is

mostly

sporadic

and

characterized

by

ventricular

enlargement

in

the

absence

of

significant

elevations

of

intracranial

pressure

therefore

this

form

is

termed

normal

pressure

hydrocephalus

-LRB-

NPH

-RRB-

Definite

changes

in

CSF

flow

resorption

and

associated

dynamics

have

been

found

in

NPH

patients

and

these

changes

may

represent

a

pathogenic

mechanism

or

a

secondary

phenomenon

-LSB-

-RSB-

Adult-onset

hydrocephalus

may

develop

either

as

a

result

of

decompensation

of

a

compensated

congenital

hydrocephalus

or

it

may

arise

de

novo

in

adult

life

secondary

to

an

acquired

disturbance

of

normal

CSF

dynamics

The

latter

may

be

due

to

late-onset

aqueductal

stenosis

or

disruption

of

normal

CSF

absorptive

pathways

-LSB-

-RSB-

Acquired

-LRB-

adult-onset

or

NPH

-RRB-

form

of

inherited

hydrocephalus

is

very

rare

Recently

an

X-linked

adult-onset

NPH

-LSB-

-RSB-

and

a

form

of

familial

NPH

that

is

transmitted

in

autosomal

dominant

fashion

-LSB-

-RSB-

have

been

reported

but

detailed

genetic

linkage

studies

have

not

been

carried

out

yet

The

genetic

etiology

of

this

form

is

therefore

totally

unknown

Hydrocephalus

has

been

observed

in

many

mammals

-LSB-

-RSB-

Animal

hydrocephalus

models

have

many

histopathological

similarities

to

humans

and

can

be

used

to

understand

the

genetics

and

pathogenesis

of

brain

damage

-LSB-

-RSB-

It

has

been

well

documented

in

the

animal

models

that

in

the

majority

of

cases

congenital

hydrocephalus

is

a

genetic

disease

Furthermore

many

congenital

hydrocephalus

loci

have

been

mapped

and

identified

in

the

animal

models

Hydrocephalic

Texas

strain

-LRB-

HTX

-RRB-

rat

model

of

inherited

congenital

hydrocephalus

is

characterized

by

onset

in

late

gestation

a

complex

mode

of

inheritance

and

ventricular

dilatation

associated

with

abnormalities

in

the

cerebral

aqueduct

and

subcommissural

organ

-LRB-

SCO

-RRB-

a

structure

that

is

important

for

the

patency

of

the

aqueduct

of

Sylvius

and

normal

CSF

flow

in

the

brain

Quantitative

trait

locus

-LRB-

QTL

-RRB-

genetic

mapping

has

been

performed

from

the

progeny

of

a

backcross

of

HTX

rat

with

the

non-hydrocephalic

Fischer

strain

The

disease

has

been

linked

with

loci

on

chromosome

-LRB-

Chr

-RRB-

-LRB-

peak

markers

-RRB-

-LRB-

between

markers

and

-RRB-

-LRB-

peak

markers

and

-RRB-

and

-LRB-

peak

markers

and

-RRB-

respectively

The

severity

of

hydrocephalus

in

HTX

rat

seems

to

be

influenced

by

different

genetic

loci

-LSB-

-RSB-

Another

study

suggested

that

the

HTX

strain

is

homozygous

carrier

of

an

autosomal

recessive

hydrocephalus

gene

with

incomplete

penetrance

-LSB-

-RSB-

The

genetics

of

another

hydrocephalus

inbred

strain

Wistar-Lewis

rats

-LRB-

LEW/Jms

-RRB-

which

demonstrate

inherited

congenital

hydrocephalus

is

less

clear

with

possible

traits

as

an

autosomal

recessive

-LSB-

-RSB-

or

semidominant

or

multigenic

-LRB-

possible

QTL

-RRB-

with

a

possible

locus

on

sex

chromosomes

-LSB-

-RSB-

but

of

the

loci

has

been

localized

In

mouse

models

three

QTL

loci

associated

with

congenital

hydrocephalus

have

been

identified

and

labeled

as

and

As

a

major

QTL

controlling

variance

in

ventricular

size

is

located

on

Chr

-LRB-

near

the

markers

and

-RRB-

The

Other

two

loci

and

show

strong

epistatic

interactions

affecting

ventricular

size

in

the

developing

embryo

is

located

on

Chr

-LRB-

near

and

-RRB-

and

is

located

on

Chr

-LRB-

between

and

-RRB-

-LSB-

-RSB-

The

autosomal

recessive

congenital

-LRB-

-RRB-

mouse

has

been

characterized

phenotypically

by

a

dome-shaped

head

that

is

sometimes

seen

at

birth

or

develops

during

the

first

weeks

Internally

dilatation

of

the

entire

ventricular

system

is

observed

-LSB-

-RSB-

A

more

severe

phenotypic

form

-LRB-

-RRB-

mouse

-LSB-

-RSB-

and

an

obstructive

hydrocephalus

-LRB-

oh

-RRB-

mouse

with

communicating

hydrocephalus

and

secondary

aqueductal

stenosis

have

also

been

described

-LSB-

-RSB-

Unfortunately

subsequent

efforts

to

identify

genetic

loci

have

not

been

done

on

these

non-inbred

mouse

strains

In

mouse

targeted

insertional

mutagenesis

the

accidental

insertion

of

a

transgene

into

a

crucial

genomic

locus

could

yield

important

information

which

has

happened

twice

in

hydrocephalus

genetic

studies

The

transgenic

mouse

line

demonstrates

autosomal

recessive

congenital

hydrocephalus

This

is

caused

by

a

Bdnf

transgene-induced

insertional

mutation

on

a

single

locus

on

mouse

Chromosome

-LRB-

near

marker

-RRB-

The

insertion

locus

is

overlapped

with

that

of

autosomal

recessive

-LRB-

-RRB-

mouse

that

phenotypically

shows

lethal

communicating

hydrocephalus

with

perinatal

onset

-LSB-

-RSB-

The

transgene

insertion

resulted

as

a

rearrangement

of

Hydin

exons

in

mice

Subsequently

a

single

CG

base-pair

deletion

in

exon

of

Hydin

was

also

discovered

in

mice

carrying

the

spontaneous

mutant

allele

-LSB-

-RSB-

In

another

targeted

insertional

mutagenesis

resulting

in

congenital

hydrocephalus

the

transgene

interferes

with

the

expression

of

a

brain-specific

isoform

of

the

regulatory

factor

-LRB-

-RRB-

which

belongs

to

the

winged

helix

transcription

factor

family

This

brain

specific

isoform

is

called

variant

transcript

or

and

is

crucial

for

normal

brain

development

as

well

as

for

the

genesis

of

the

SCO

Loss

of

a

single

allele

prevents

formation

of

the

SCO

and

leads

to

an

autosomal

dominant

congenital

hydrocephalus

This

obstructive

hydrocephalus

appeared

to

be

secondary

to

failure

of

development

of

the

SCO

-LSB-

-RSB-

The

autosomal

recessive

congenital

hydrocephalus

-LRB-

ch

-RRB-

mouse

was

reported

decades

ago

-LSB-

-RSB-

Recently

this

mouse

has

been

shown

to

have

a

mutation

on

another

winged

helix/forkhead

transcription

factor

gene

-LRB-

-RRB-

on

mouse

Chromosome

-LSB-

-RSB-

There

is

a

recent

report

of

children

with

hydrocephalus

from

different

families

with

subtelomeric

deletions

from

chromosome

Three

forkhead

genes

within

this

region

-LRB-

and

-RRB-

or

proximal

to

it

-LRB-

-RRB-

were

evaluated

as

potential

candidate

disease

genes

but

no

disease

causing

mutations

were

identified

-LSB-

-RSB-

The

autosomal

recessive

hydrocephalus

with

hop

gait

-LRB-

hyh

-RRB-

mouse

exhibits

dramatic

dilation

of

the

ventricles

at

birth

and

invariably

develops

hopping

gait

The

hyh

mouse

shows

a

markedly

small

cerebral

cortex

at

birth

and

dies

postnatally

from

progressive

enlargement

of

the

ventricular

system

The

small

cortex

in

hyh

mouse

reflects

altered

development

of

the

neuronal

cells

In

this

mouse

it

is

postulated

that

neural

progenitor

cells

withdraw

prematurely

from

the

cell

cycle

producing

more

early-born

deep-layer

cerebral

cortical

neurons

but

depleting

the

cortical

progenitor

pool

and

creating

a

small

cortex

Genetic

linkage

analysis

localized

the

hyh

locus

between

markers

and

on

mouse

Chr

Later

the

hyh

gene

was

identified

as

α-SNAP

-LRB-

soluble

NSF

attachment

protein

α

-RRB-

-LSB-

-RSB-

Homozygous

mutant

mice

harbor

a

missense

mutation

in

a

conserved

residue

in

one

of

the

α-helical

domains

The

hyh

mutant

was

not

a

allele

and

is

expressed

however

the

mutant

protein

is

less

abundant

in

hyh

mice

The

autosomal

recessive

hemorrhagic

hydrocephalus

-LRB-

hhy

-RRB-

homozygous

mutant

mouse

has

dilated

lateral

ventricles

and

a

patent

aqueduct

with

no

histological

abnormalities

either

in

the

subarachnoid

space

or

in

the

choroid

plexus

Multiple

hemorrhages

in

the

meninges

and

throughout

the

brain

parenchyma

can

be

observed

in

the

advanced

stages

of

hydrocephalus

The

hhy

locus

has

been

localized

on

mouse

Chr

-LSB-

-RSB-

Recently

several

new

congenital

hydrocephalus

models

have

emerged

in

zebra

fish

mutagenesis

screening

These

models

have

been

shown

to

have

the

defects

in

embryogenesis

and

early

development

leading

to

enlarged

brain

ventricles

However

genetic

loci

for

these

models

have

not

been

identified

yet

-LSB-

-RSB-

Genetic

studies

in

animal

models

have

started

to

open

the

way

for

understanding

the

underlying

pathology

of

hydrocephalus

In

contrast

to

research

with

animal

models

human

hydrocephalus

genetic

research

has

lagged

far

behind

To

date

at

least

mutants

of

hydrocephalus

have

been

described

and

congenital

hydrocephalus

genes

have

been

identified

Among

them

only

one

hydrocephalus

gene

has

been

identified

in

humans

-LRB-

see

Table

-RRB-

Table

of

current

known

loci

-LRB-

or

mutants

-RRB-

of

hydrocephalus

in

vertebratesSpeciesStrainClinical

formTrait

LocusChromosomeHuman

syntenic

regionHuman

or

unknown

-LRB-

QTL

-RRB-

Genetic

trait

AR

autosomal

recessive

AD

autosomal

dominant

QTL

Quantitative

trait

locus

clinicalform

C

congenital

AO

Adut-Onset

Developmental

physiological

and

anatomical

pathology

of

hydrocephalus

The

neuropathology

of

hydrocephalus

has

been

adequately

elucidated

Cerebral

ventricle

dilatation

secondary

to

disturbed

CSF

flow

has

been

observed

as

an

inheritable

trait

in

a

variety

of

laboratory

animals

-LRB-

as

well

as

in

humans

-RRB-

In

most

cases

defective

development

of

the

cerebral

aqueduct

or

the

subarachnoid

space

has

been

observed

-LSB-

-RSB-

Affected

individuals

may

have

severe

developmental

delay

and

radiographic

findings

of

hydrocephalus

-LSB-

-RSB-

The

morphological

and

developmental

changes

in

the

ventricular

system

have

been

well

studied

in

three

major

rat

models

of

congenital

hydrocephalus

-LRB-

-RRB-

induced

LEW/Jms

and

HTX

mutant

rats

Comparative

morphological

studies

revealed

that

hydrocephalus

was

comparable

to

the

Dandy-Walker

syndrome

The

LEW/Jms

and

HTX

mutant

models

were

identical

with

regard

to

the

form

of

presentation

and

progression

of

hydrocephalus

in

the

postnatal

period

but

the

pathogenesis

of

these

two

conditions

in

the

fetal

period

was

different

The

LEW/Jms

rats

showed

primary

congenital

aqueductal

stenosis

in

early

prenatal

life

and

the

hydrocephalic

state

appeared

before

pulmonary

maturation

was

completed

However

although

the

model

has

been

considered

to

be

of

congenital

communicating

hydrocephalus

-LSB-

-RSB-

the

HTX

fetuses

demonstrated

secondary

closure

of

the

aqueduct

in

the

perinatal

period

This

secondary

closure

of

the

aqueduct

in

HTX

rats

is

believed

to

be

due

to

retrograde

degeneration

of

the

thalamus

caused

by

apoptotic

cell

death

-LSB-

-RSB-

and

failure

in

cell

proliferation

-LSB-

-RSB-

The

HTX

rat

also

shows

a

reduction

in

the

secretory

cells

of

the

SCO

Regarding

the

role

of

the

SCO

in

hydrocephalus

pathogenesis

serial

brain

sections

through

aqueduct

regions

containing

the

SCO

from

HTX

rats

in

comparison

with

normal

Fischer

strain

have

been

studied

and

found

that

reduced

SCO

glycoprotein

immunoreactivity

precedes

both

aqueduct

closure

and

expansion

of

the

lateral

ventricles

in

the

HTX

rate

-LRB-

as

it

's

redundant

-RRB-

-LSB-

-RSB-

Although

some

studies

have

addressed

the

activation

of

macrophages

and

microglia

-LRB-

the

resident

mononuclear

phagocytes

of

the

brain

-RRB-

within

the

brain

in

animal

hydrocephalus

models

little

is

known

of

their

state

of

activation

or

regional

distribution

in

human

congenital

hydrocephalus

In

one

experiment

brain

tissue

samples

of

human

fetal

cases

with

hydrocephalus

and

non-hydrocephalic

controls

were

stained

immunohistochemically

with

antibodies

directed

against

MHC

class

II

and

antigens

and

lectin

histochemistry

was

done

with

tomato

lectin

Hydrocephalus

cases

showed

focal

collections

of

and

tomato

lectin-positive

macrophages

along

the

ependymal

lining

of

the

lateral

ventricles

particularly

within

the

occipital

horn

By

comparison

brain

tissue

samples

from

controls

showed

few

or

no

ependymal

or

supraependymal

macrophages

and

the

few

macrophages

that

were

present

were

not

as

intensely

immunoreactive

as

in

the

hydrocephalus

cases

The

macrophage

response

detected

at

the

ependymal

lining

of

the

ventricles

and

within

the

periventricular

area

in

hydrocephalus

may

be

related

both

to

the

severity

of

hydrocephalus

and

the

age

of

the

fetus

-LSB-

-RSB-

Microglia

that

are

normally

interspersed

throughout

the

intermediate

zone

and

circumscribing

the

basal

ganglia

were

within

normal

confines

in

all

cases

examined

Unexpectedly

hydrocephalic

cases

also

showed

focal

regions

of

hypovascularization

or

alterations

in

the

structure

and

orientation

of

capillaries

within

periventricular

areas

compared

with

controls

-LSB-

-RSB-

In

summary

the

pathological

studies

of

hydrocephalus

clearly

indicate

that

impaired

and

abnormal

brain

development

in

the

early

development

stage

caused

by

altered

neural

cell

fate

and

perturbed

regulation

of

cellular

proliferation

and

apoptosis

The

abnormal

brain

development

subsequently

leads

to

the

accumulation

of

the

CSF

in

cerebral

cavities

All

these

cellular

and

developmental

events

eventually

lead

to

the

congenital

hydrocephalus

accompanied

by

possible

secondary

inflammatory

reaction

and

neurovascular

pathogenesis

The

molecular

and

cellular

etiology

of

hydrocephalus

One

of

the

possible

mechanisms

leading

to

the

pathogenesis

of

hydrocephalus

is

the

disruption

of

neural

cell

membrane

proteins

that

play

an

important

function

during

brain

development

The

protein

coded

by

human

X-linked

hydrocephalus

gene

is

a

member

of

the

immunoglobulin

superfamily

of

neural

cell

adhesion

molecules

that

is

expressed

in

neurons

and

Schwann

cells

and

seems

to

be

essential

for

the

brain

development

and

function

Hirschsprung

's

disease

-LRB-

HSCR

-RRB-

is

characterized

by

the

absence

of

ganglion

cells

and

the

presence

of

hypertrophic

nerve

trunks

in

the

distal

bowel

There

have

been

several

reports

of

patients

with

X-linked

hydrocephalus

and

HSCR

with

a

mutation

in

the

gene

Therefore

decreased

may

also

be

a

modifying

factor

in

the

development

of

HSCR

-LSB-

-RSB-

The

gene

carrying

the

mutation

for

autosomal

recessive

hydrocephalus

in

the

hyh

mouse

codes

α-SNAP

protein

α-SNAP

is

essential

for

apical

protein

localization

and

cell

fate

determination

in

neuroepithelial

cells

-LSB-

-RSB-

α-SNAP

plays

a

key

role

in

a

wide

variety

of

membrane

fusion

events

in

eukaryotic

cells

Membrane

fusion

is

required

for

two

main

cellular

functions

-RRB-

the

transport

of

molecules

to

distinct

inter

and

intracellular

compartments

and

thereby

maintenance

of

the

functional

and

structural

organization

of

eukaryotic

cells

-RRB-

the

intercellular

communication

such

as

the

regulated

exocytosis

-LRB-

secretion

-RRB-

of

neurotransmitters

by

neuronal

cell

which

occurs

temporally

and

spatially

as

the

precise

sequential

regulation

events

at

the

plasma

membrane

during

the

early

brain

development

-LSB-

-RSB-

In

the

hyh

mouse

model

altered

neural

cell

fate

is

also

accompanied

by

abnormal

localization

of

many

apical

proteins

implicated

in

regulation

of

neural

cell

fate

including

E-cadherin

beta-catenin

atypical

protein

kinase

C

-LRB-

aPKC

-RRB-

inactivation-no-afterpotential

D-like

-LRB-

INADL

-RRB-

SNAP

receptor

-LRB-

SNARE

-RRB-

and

vesicle-associated

membrane

-LRB-

-RRB-

-LSB-

-RSB-

Furthermore

disturbed

astrocyte

metabolism

in

the

early

brain

development

in

the

kaolin-induced

rat

model

of

hydrocephalus

has

also

been

reported

-LSB-

-RSB-

Hydrocephalus

may

also

be

caused

by

a

malfunction

of

the

ependymal

cells

-LSB-

-RSB-

Within

the

neonatal

brain

of

the

mouse

the

protein

-LRB-

hydin

-RRB-

is

confined

to

the

ciliated

ependymal

cell

layer

lining

the

lateral

third

and

fourth

ventricles

Hydin

is

not

closely

related

to

any

previously

known

protein

with

the

exception

of

a

amino

acid

domain

with

homology

to

caldesmon

an

actin-binding

protein

suggesting

that

hydin

interacts

with

the

cytoskeleton

-LSB-

-RSB-

The

protein

of

axonemal

heavy

chain

gene

-LRB-

-RRB-

dynein

is

also

specifically

expressed

in

ependymal

cells

and

is

essential

for

ultra

structural

and

functional

integrity

of

ependymal

cilia

In

mice

lack

of

ependymal

flow

causes

closure

of

the

aqueduct

and

subsequent

formation

of

triventricular

hydrocephalus

during

early

postnatal

brain

development

The

higher

incidence

of

aqueductal

stenosis

and

hydrocephalus

formation

in

patients

with

ciliary

defects

proves

the

relevance

of

this

novel

mechanism

in

humans

-LSB-

-RSB-

Hydrocephalus

may

be

caused

by

malfunction

of

mesenchymal

cells

In

mice

is

a

regulatory

gene

involved

in

epithelio-mesenchymal

interactions

in

limb

formation

and

organogenesis

In

the

embryonic

brain

the

gene

is

expressed

along

the

dorsal

midline

The

most

important

features

observed

in

homozygous

mutants

were

the

absence

or

malformation

of

the

posterior

commissure

-LRB-

PC

-RRB-

and

of

the

SCO

the

collapse

of

the

cerebral

aqueduct

and

the

development

of

hydrocephalus

The

heterozygous

mutants

developed

an

abnormal

PC

and

smaller

SCO

as

revealed

by

specific

antibodies

against

SCO

secretory

glycoproteins

About

one

third

of

the

heterozygous

mutants

also

developed

hydrocephalus

therefore

the

phenotype

may

be

determined

by

the

gene

dosage

during

a

specific

developmental

period

-LSB-

-RSB-

In

the

autosomal

recessive

congenital

hydrocephalus

-LRB-

ch

-RRB-

mouse

model

a

truncated

protein

lacking

the

DNA-binding

domain

of

the

forkhead/winged

helix

gene

was

generated

Mesenchymal

cells

from

embryos

differentiate

poorly

into

cartilage

in

micromass

culture

and

do

not

respond

to

added

bone

morphogenetic

protein

-LRB-

-RRB-

and

transforming

growth

factor-beta

-LRB-

-RRB-

The

differentiation

of

arachnoid

cells

in

meninges

of

the

mutant

mice

is

also

abnormal

The

levels

of

developmental

growth

factors

such

as

and

are

dramatically

increased

in

the

ch

mouse

and

it

is

possible

that

phenotypic

hydrocephalus

of

mouse

is

due

to

the

secondary

effect

of

these

elevated

growth

factors

Corresponding

to

studies

in

the

ch

mouse

human

patients

with

deletions

in

the

region

containing

human

homolog

were

found

to

develop

multiple

developmental

disorders

including

hydrocephalus

-LSB-

-RSB-

Another

winged

helix

transcription

factor

causing

congenital

hydrocephalus

when

mutated

transcript

is

dynamically

expressed

in

the

developing

brain

from

the

neural

plate

stages

The

RFX

proteins

belong

to

the

winged-helix

subfamily

of

helix-turn-helix

transcription

factors

and

bind

to

X-boxes

in

target

DNA

sequences

and

regulate

expression

of

the

downstream

target

genes

-LSB-

-RSB-

Disruption

of

both

alleles

by

insertional

mutagenesis

severely

alters

early

brain

morphogenesis

reduces

expression

and

causes

a

deficiency

in

WNT

signaling

-LSB-

-RSB-

This

may

suggest

that

is

probably

upstream

of

in

the

signaling

pathway

during

early

brain

development

Hydrocephalus

may

be

caused

by

perturbation

of

growth

factor

signaling

-LSB-

-RSB-

Developmental

abnormalities

in

congenital

hydrocephalus

provide

the

clues

for

the

perturbation

of

major

signaling

pathways

in

the

development

-LSB-

-RSB-

TGFB

is

an

important

cytokine

and

growth-signaling

molecule

in

the

brain

In

mouse

models

severe

hydrocephalus

has

been

observed

in

transgenic

mouse

overexpression

of

in

astrocytes

-LSB-

-RSB-

In

the

HTX

rat

increased

level

of

may

contribute

to

the

development

of

hydrocephalus

-LSB-

-RSB-

In

mouse

models

fibroblast

growth

-LRB-

-RRB-

seems

to

play

a

predominant

role

in

the

proliferation

of

neuronal

precursors

and

in

neuronal

differentiation

in

the

developing

cerebral

cortex

even

at

relatively

late

stages

of

brain

neurogenesis

Administration

of

to

embryonic

brain

induces

hydrocephalic

brain

morphology

and

aberrant

differentiation

of

neurons

in

the

postnatal

cerebral

cortex

-LSB-

-RSB-

IGF

binding

-LRB-

-RRB-

modulates

the

cellular

action

of

insulin-like

growth

factors

-LRB-

IGFs

-RRB-

some

of

which

are

expressed

in

the

fetal

brain

Hydrocephalus

has

been

observed

in

mouse

models

that

overexpress

liver-specific

during

fetal

life

The

hepatic

over-expression

of

may

have

endocrine

effects

on

brain

development

and

induction

of

congenital

hydrocephalus

-LSB-

-RSB-

Other

studies

have

shown

that

up-regulation

of

certain

growth

factors

in

the

brain

could

lead

to

altered

brain

fluid

dynamics

-LSB-

-RSB-

is

a

member

of

the

suppressor

of

cytokine

signaling

-LRB-

SOCS

-RRB-

protein

family

SOCS

proteins

have

a

similar

structure

an

N-terminal

domain

of

variable

length

a

central

Src

domain

and

a

C-terminal

SOCS

box

Biochemical

and

genetic

studies

have

revealed

that

SOCS

family

members

play

an

important

role

in

the

termination

of

cytokine

and

growth

factor

signaling

Homozygous

mutant

mice

were

born

in

expected

numbers

were

fertile

and

did

not

exhibit

defects

in

hematopoiesis

or

circulating

glucose

or

insulin

concentrations

Strikingly

however

these

homozygous

mice

were

smaller

than

their

wild-type

littermates

and

within

weeks

of

age

approximately

of

the

homozygous

mice

died

as

a

result

of

hydrocephalus

In

situ

hybridization

studies

in

normal

mice

have

revealed

that

is

prominently

expressed

in

the

brain

suggesting

that

plays

an

important

functional

role

in

early

brain

development

-LSB-

-RSB-

We

can

therefore

hypothesize

that

loss

of

function

will

lead

to

increased

expression

of

cytokines

resulting

in

developmental

abnormalities

and

congenital

hydrocephalus

due

to

its

inhibitory

role

in

cytokine

signaling

Hydrocephalus

may

also

be

caused

by

the

disruption

of

extracellular

matrix

-LRB-

ECM

-RRB-

In

the

over-expression

mouse

model

the

changing

expressions

of

a

remodeling

protein

matrix

-LRB-

-RRB-

and

its

specific

inhibitor

tissue

inhibitor

of

-LRB-

-RRB-

were

also

found

to

be

important

factors

in

the

spontaneous

development

of

hydrocephalus

by

altering

the

ECM

environment

-LSB-

-RSB-

Furthermore

increased

expression

of

cytokines

such

as

might

also

reciprocally

play

an

important

role

by

disrupting

the

vascular

ECM

remodeling

promoting

hemorrhages

and

altering

the

re-absorption

of

CSF

-LSB-

-RSB-

In

another

mouse

model

ablation

of

the

nonmuscle

myosin

heavy

chain

II-B

-LRB-

NMHC-B

-RRB-

results

in

severe

hydrocephalus

with

enlargement

of

the

lateral

and

third

ventricles

These

defects

may

be

caused

by

abnormalities

in

the

cell

adhesive

properties

of

neuroepithelial

cells

and

suggest

that

NMHC-B

is

essential

for

both

early

and

late

developmental

processes

in

the

mammalian

brain

-LSB-

-RSB-

Hydrocephalus

may

also

be

caused

by

the

disruption

of

major

early

brain

developmental

patterning

molecules

Autosomal

dominant

hydrocephalus

in

mutation

mice

is

characterized

by

eminent

dilatation

of

lateral

ventricles

and

a

ballooned

cerebrum

Histopathology

shows

edematous

change

of

the

periventricular

white

matter

suggesting

that

functions

as

a

brain

developmental

organizer

and

a

disruption

of

this

gene

is

a

likely

cause

of

hydrocephalus

-LSB-

-RSB-

In

conclusion

many

genetic

loci

of

hydrocephalus

have

been

defined

in

animal

models

which

is

building

a

foundation

for

better

understanding

of

molecular

etiology

of

hydrocephalus

however

genetic

research

of

hydrocephalus

in

humans

is

limited

The

histopathological

similarities

of

animal

models

can

be

used

to

understand

the

genetics

and

pathogenesis

of

human

hydrocephalus

For

example

the

histopathological

and

morphological

appearance

of

hydrocephalic

HTX

rats

is

demonstrated

in

Fig.

in

which

hydrophilic

HTX

rat

exhibits

large

cerebral

ventricles

a

progressively-thinned

cortical

mantle

and

stretched

internal

capsule

fibers

-LSB-

-RSB-

Review

of

the

molecular

etiologies

shows

a

very

diverse

set

of

pathogenetic

mechanisms

Perturbation

of

almost

any

molecule

that

plays

a

crucial

role

in

early

brain

development

and

sequentially

regulation

of

dynamics

of

cerebrospinal

fluid

could

lead

to

the

pathogenesis

of

congenital

hydrocephalus

The

known

hydrocephalus

genes

mostly

code

for

important

cytokines

growth

factors

or

related

molecules

in

the

cellular

signal

pathways

during

early

brain

development

Fig.

of

rat

brain

morphology

by

MRI

and

histology

at

and

days

of

age

in

non-hydrocephalic

and

hydrocephalic

HTX

rats

MRI

scans

of

coronal

sections

from

a

non-hydrocephalic

HTX

rat

at

the

level

of

the

thalamus

at

and

days

-LRB-

A

D

G

-RRB-

shows

small

ventricular

and

subarachnoid

spaces

compared

to

an

age-matched

HTX

littermate

-LRB-

B

E

H

-RRB-

that

exhibits

large

cerebral

ventricles

a

progressively-thinned

cortical

mantle

and

stretched

internal

capsule

fibers

-LRB-

-RRB-

Congenital

closure

of

the

cerebral

aqueduct

becomes

life-threatening

by

days

of

age

Histological

sections

-LRB-

C

F

I

-RRB-

at

the

level

of

the

midbrain

at

the

same

ages

demonstrate

extreme

thinning

of

the

cortical

mantle

MRI

images

are

modified

from

Jones

et

al

-LRB-

-RRB-

-LSB-

-RSB-

with

permission

by

Maney

Publishing

histological

samples

are

from

the

doctoral

thesis

of

Janet

M.

Miller

PhD

Future

prospects

It

is

essential

to

recognize

that

molecular

genetics

is

the

only

current

scientific

approach

that

can

be

used

to

study

hydrocephalus

in

which

the

usual

concern

about

whether

an

observed

phenomenon

is

a

consequence

or

a

cause

is

completely

addressed

Despite

our

knowledge

of

the

genetics

of

hydrocephalus

in

animal

models

we

have

very

limited

knowledge

about

the

genetic

and

molecular

mechanisms

that

cause

human

hydrocephalus

Without

this

knowledge

it

is

impossible

to

say

whether

the

pathogenesis

of

human

hydrocephalus

is

comparable

to

that

seen

in

animal

models

and

impractical

to

extrapolate

data

gained

from

animal

models

to

humans

In

order

to

better

understand

human

hydrocephalus

and

to

develop

more

appropriate

translational

research

it

will

be

necessary

to

conduct

large-scale

genetic

studies

of

human

hydrocephalus

If

and

when

more

heritable

forms

of

human

hydrocephalus

are

identified

and

underlying

genes

and

their

functions

are

characterized

then

this

knowledge

could

be

used

to

improve

patient

care

in

a

variety

of

different

ways

such

as

prenatal

diagnosis

and

new

potential

therapeutic

approaches

Possible

new

mechanisms

other

than

altered

CSF

circulation

and

resorption

if

uncovered

via

the

genetic

research

may

also

help

explain

why

patients

with

hydrocephalus

may

experience

symptomatic

progression

despite

functioning

shunts

Efforts

to

identify

genetic

variants

associated

with

susceptibility

to

genetic

diseases

rely

on

three

major

approaches

pedigree

and

sib-pair

linkage

analysis

and

population

association

studies

The

differences

among

these

study

designs

reflect

their

derivation

from

biological

versus

epidemiological

traits

Like

most

common

diseases

it

would

be

very

difficult

to

identify

and

recruit

large

pedigrees

in

hydrocephalus

that

show

hereditary

transmission

of

the

condition

Therefore

the

last

two

approaches

sib-pair

linkage

analysis

and

population

association

studies

are

the

best

options

for

the

genetic

study

on

this

disease

For

any

study

but

particularly

in

the

case

of

genetic

mapping

for

a

common

disease

a

large

sample

size

is

crucial

in

achieving

statistical

significance

Recent

advances

in

the

genomics

and

statistical

methodology

in

genetic

mapping

will

certainly

help

in

making

well-powered

studies

more

feasible

by

reducing

the

number

of

genetic

markers

or

workload

required

for

these

studies

For

example

since

many

genes

and

loci

response

for

hydrocephalus

in

animal

models

have

been

mapped

candidate

genes

approach

will

certainly

be

the

very

first

choice

to

test

the

collected

human

hydrocephalus

population

for

linkage

and

association

analysis

In

collaboration

with

the

Hydrocephalus

Association

-LRB-

HA

-RRB-

our

group

has

initiated

a

genetic

study

of

human

hydrocephalus

As

part

of

a

prospective

study

that

has

been

approved

by

the

Johns

Hopkins

Institutional

Review

Board

we

are

collecting

blood

samples

from

both

congenital

and

acquired

NPH

hydrocephalus

patients

The

objectives

of

this

study

are

to

identify

the

genetic

loci

responsible

for

the

development

of

hydrocephalus

to

examine

the

relationship

between

genotype

and

phenotype

and

to

define

the

functions

of

these

genes

during

early

development

This

is

the

first

large-scale

research

study

of

its

kind

and

information

gained

from

this

study

will

undoubtedly

provide

invaluable

information

concerning

the

developmental

mechanisms

of

this

disease

in

humans

Such

knowledge

will

hopefully

lead

to

the

more

reasonable

treatment

schemes

the

better

diagnostic

tools

and

the

more

effective

therapeutic

modalities

O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O B O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O B B O O B O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O B O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O B B O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Improving

Web

Searches

Case

Study

of

Quit-Smoking

Web

Sites

for

Teenagers

Background

The

Web

has

become

an

important

and

influential

source

of

health

information

With

the

vast

number

of

Web

sites

on

the

Internet

users

often

resort

to

popular

search

sites

when

searching

for

information

However

little

is

known

about

the

characteristics

of

Web

sites

returned

by

simple

Web

searches

for

information

about

smoking

cessation

for

teenagers

Introduction

The

World

Wide

Web

with

over

million

public

Web

sites

and

over

billion

Web

pages

-LSB-

-RSB-

has

become

an

important

and

influential

source

of

health

information

-LSB-

-RSB-

In

September

there

were

an

estimated

million

people

online

worldwide

-LSB-

-RSB-

In

the

United

States

-LRB-

million

-RRB-

of

the

children

and

adolescents

between

the

ages

of

and

use

computers

and

of

the

to

year

olds

use

the

Internet

-LSB-

-RSB-

With

the

vast

amount

and

dynamic

nature

of

information

on

the

World

Wide

Web

it

is

not

surprising

to

find

that

over

of

those

online

use

search

sites

to

navigate

the

Web

-LSB-

-RSB-

However

the

amount

of

results

returned

from

a

search

is

often

overwhelming

For

example

results

were

found

with

the

search

terms

teen

quit

smoking

in

Google

Of

the

several

thousand

search

sites

or

directories

-LSB-

-RSB-

only

a

few

are

of

high

popularity

as

indicated

by

their

audience

reach

and

time

spent

on

them

-LSB-

-RSB-

Although

Google

will

provide

up

to

a

thousand

results

from

a

query

few

users

are

likely

to

examine

them

all

In

an

observational

study

on

adult

subjects

only

participants

ever

looked

beyond

the

first

search

pages

and

only

of

them

ever

clicked

a

link

on

those

pages

-LSB-

-RSB-

A

survey

done

in

on

e-mail

participants

showed

that

only

of

the

users

went

beyond

the

second

page

-LSB-

-RSB-

Another

pilot

study

of

teenagers

found

they

looked

past

the

fourth

page

of

results

less

than

of

the

time

-LSB-

-RSB-

Thus

position

ranking

in

Web-search

results

especially

on

the

first

few

pages

is

an

important

determinant

of

information

accessibility

by

users

Several

studies

have

reported

substantial

variability

in

health-related

Web-site

content

-LSB-

-RSB-

While

guidelines

for

evaluating

the

quality

of

health

information

on

the

Web

are

available

-LSB-

-RSB-

the

correlation

between

these

guidelines

and

accuracy

of

health

information

is

debated

-LSB-

-RSB-

Position

ranking

in

search

results

was

not

associated

with

content

quality

-LSB-

-RSB-

Using

the

search

term

breast

cancer

Meric

et

al

-LSB-

-RSB-

reported

that

popularity

of

Web

sites

was

associated

with

type

rather

than

quality

of

content

In

a

sample

of

Web

sites

that

provided

information

on

urinary

incontinence

the

Internet

popularity

indexes

as

measured

by

the

number

of

links

to

the

main

incontinence

page

of

each

Web

site

and

by

the

number

of

links

to

all

pages

of

each

Web

site

divided

by

the

number

of

pages

of

the

site

were

not

correlated

with

a

quality

score

based

on

Silberg

et

al

-LSB-

-RSB-

and

the

HONcode

principles

-LSB-

-RSB-

The

aim

of

this

study

was

-LRB-

a

-RRB-

to

identify

the

characteristics

of

Web

sites

with

information

on

smoking

cessation

for

teenagers

that

ranked

in

the

top

positions

in

a

typical

Web

search

on

popular

search

sites

and

-LRB-

b

-RRB-

to

evaluate

the

association

between

those

characteristics

and

the

position

ranking

for

sites

that

are

of

direct

relevance

to

smoking

cessation

for

teenagers

The

findings

are

relevant

for

improving

consumer

access

to

health

information

Methods

This

study

was

carried

out

from

May

through

June

Web

sites

with

information

on

smoking

cessation

for

teenagers

were

identified

with

popular

search

sites

using

a

specific

search

term

The

characteristics

of

the

identified

sites

were

collected

with

a

Web-site

characteristic

checklist

raters

evaluated

each

Web

site

independently

-LRB-

details

below

-RRB-

Search

Protocol

Four

popular

search

sites

-LRB-

Table

-RRB-

were

used

in

this

study

Users

spend

over

million

search

hours

per

month

at

each

site

A

search

hour

equals

the

number

of

visitors

to

a

site

multiplied

by

the

average

number

of

hours

each

visitor

is

estimated

to

have

spent

at

the

site

Table

Popular

search

sites

in

the

United

States

Search

Site

URL

Total

Search

Hours

-LRB-

Millions

of

Hours

-RRB-

in

January

MainUnderlying

SearchEngine

Google

Google

AOL

search.aol.com

Google

Yahoo!

Google

and

Overture

-LRB-

for

paid

listings

-RRB-

MSN

search.msn.com

LookSmart

Inktomi

Microsoft

proprietary

editor

and

Overture

-LRB-

for

paid

listings

-RRB-

Source

Search

Engine

Watch

-LSB-

-RSB-

The

search

term

on

smoking

cessation

for

teenagers

was

selected

based

on

information

from

the

Overture

Search

Term

Suggestion

Tool

-LSB-

-RSB-

and

the

Keyword

Suggestion

Tool

-LSB-

-RSB-

These

sites

provide

a

count

of

the

search

terms

that

were

submitted

to

their

search

engines

Overture

provides

their

search

results

to

various

popular

search

sites

including

Yahoo

MSN

AltaVista

Lycos

HotBot

and

AllTheWeb

-LSB-

-RSB-

For

example

in

April

there

were

searches

submitted

to

Overture

with

quit

smoking

with

stop

smoking

and

with

smoking

cessation

Various

other

combinations

of

teen

youth

adolescent

quit

smoking

stop

smoking

and

smoking

cessation

were

compared

Based

on

the

frequency

of

searches

performed

on

the

Web

as

recorded

by

the

Overture

database

the

search

terms

teen

quit

smoking

were

submitted

to

the

search

sites

to

locate

sites

with

information

on

smoking

cessation

for

teenagers

To

mimic

the

search

behavior

of

Web

users

only

the

top

search

results

were

included

in

the

study

Sites

ranking

below

the

top

results

are

likely

to

be

found

only

by

more-persistent

searchers

-LSB-

-RSB-

Thirty

results

are

equivalent

to

pages

-LRB-

clicks

-RRB-

of

the

default

number

of

results

per

page

in

Google

and

AOL

such

pages

-LRB-

click

-RRB-

in

MSN

and

one

and

a

half

such

pages

-LRB-

one

click

-RRB-

in

Yahoo

The

results

from

the

search

sites

were

combined

into

one

list

to

provide

an

overall

picture

of

the

search

activity

on

the

Web

The

sites

were

reranked

by

first

grouping

the

sites

into

groups

by

the

number

of

search

sites

that

included

them

-LRB-

to

search

sites

-RRB-

and

then

by

the

position

ranking

provided

by

the

search

results

within

each

group

The

top

reranked

sites

formed

the

sample

for

the

analysis

Since

the

rankings

of

Web

sites

within

search-site

results

change

frequently

the

search

results

were

captured

in

spreadsheet

format

using

the

Google

API

Search

Tool

-LSB-

-RSB-

The

Web

pages

of

sites

identified

by

search

results

were

captured

using

Offline

Explorer

software

-LSB-

-RSB-

to

facilitate

the

recall

of

the

exact

page

content

when

necessary

and

to

provide

consistency

for

the

raters

Table

Site

characteristics

and

correlation

with

search

ranking

for

sites

relevant

to

teenagers

who

are

seeking

information

on

smoking

cessation

Site

Characteristic

Inter-Rater

Reliability

-LRB-

Kappa

-RRB-

Characteristics

Number

-LRB-

-RRB-

Kendall

Rank

Correlation

Tau

-LRB-

P

value

-RRB-

Essential

Search

feature

in

the

site

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Site

navigation

system

on

page

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Privacy

statement

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Disclaimer

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Readability

grade

level

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

Broken

links

on

page

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Enhancement

Indication

of

sponsorship

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Pop-up

advertisements

or

banner

advertisements

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Contact

e-mail

address

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Phone

number

or

mailing

address

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Content

on

cessation

method

behavioral

approach

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Content

on

cessation

method

medication

approach

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Content

on

cessation

method

alternative

approach

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Annotated

external

hyperlinks

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Interactive

component

-LRB-

quiz

game

or

bulletin

board

-RRB-

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Material

in

video

or

audio

format

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Technical

Page

size

-LRB-

kilobyte

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

Meta

description

tag

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Meta

keywords

tag

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Persistent

cookies

Present

-LRB-

-RRB-

-LRB-

-RRB-

Absent

-LRB-

-RRB-

Part

of

a

larger

Web

site

Yes

-LRB-

-RRB-

-LRB-

-RRB-

No

-LRB-

-RRB-

Link

density

-LRB-

reverse

links

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

-LRB-

-RRB-

Not

applicable

Kappa

values

for

these

characteristics

were

not

available

because

they

were

analyzed

by

the

WebXact

Watchfire

Page

Analysis

-LSB-

-RSB-

except

for

readability

grade

level

which

was

evaluated

by

only

rater

Checklist

of

Web-Site

Characteristics

A

checklist

was

uses

to

evaluate

the

characteristics

of

the

Web

sites

-LRB-

see

Table

for

checklist

items

-RRB-

The

readability

was

estimated

by

the

Flesch-Kincaid

grade-level

score

-LSB-

-RSB-

-LRB-

The

Flesch-Kincaid

grade-level

score

rates

text

on

a

United

States

grade-school

level

For

example

a

score

of

means

that

an

eighth

grader

can

understand

the

document

-RRB-

Sample

passages

from

the

Web

pages

with

information

pertaining

to

smoking

cessation

of

the

identified

sites

were

pasted

into

Microsoft

Word

XP

for

Windows

to

obtain

the

score

The

results

were

recorded

in

a

spreadsheet

and

subsequently

imported

into

SPSS

-LSB-

-RSB-

for

analysis

The

number

of

broken

links

page

size

presence

of

meta

tags

and

presence

of

persistent

cookies

were

obtained

from

WebXact

Watchfire

Page

Analysis

-LSB-

-RSB-

-LRB-

Meta

tags

are

HTML

-LSB-

hypertext

markup

language

-RSB-

tags

that

provide

information

about

the

content

of

a

Web

page

for

indexing

by

search

engines

but

do

not

affect

how

a

Web

page

is

displayed

by

a

browser

-RRB-

Link

density

was

obtained

by

using

a

reverse-lookup

query

-LRB-

link

siteURL

where

siteURL

is

replaced

by

the

Web

site

's

URL

-RRB-

in

Google

The

link

density

of

a

site

is

the

number

of

external

sites

that

have

a

link

to

that

site

A

site

with

a

higher

link

density

is

generally

more

likely

to

be

found

by

visitors

because

they

may

find

it

through

the

external

sites

Statistical

Analysis

Correlations

between

position

ranking

and

the

Web-site

characteristics

were

calculated

using

the

Kendall

rank

correlation

The

value

of

the

coefficient

-LRB-

tau

-RRB-

ranges

from

to

A

value

of

zero

indicates

no

correlation

values

near

indicate

a

strong

direct

correlation

and

values

near

indicate

a

strong

inverse

correlation

Interobserver

reliability

between

the

raters

was

calculated

using

Kappa

statistics

on

all

variables

except

readability

link

density

and

those

returned

by

WebXact

Watchfire

Page

Analysis

We

regarded

P

as

statistically

significant

Results

Of

the

top

sites

identified

by

the

search

sites

using

the

search

terms

teen

quit

smoking

only

were

relevant

to

teenagers

who

are

seeking

information

on

smoking

cessation

We

also

evaluated

the

search

results

from

Google

by

using

other

similar

search

terms

The

number

of

relevant

sites

ranged

from

to

-LRB-

Table

-RRB-

Although

we

used

only

search

site

to

illustrate

the

effect

of

search

terms

on

the

type

of

Web

sites

found

the

result

should

be

similar

at

other

search

sites

Characteristics

of

the

Relevant

Web

Sites

The

characteristics

of

the

sites

are

summarized

in

categories

-LRB-

Table

-RRB-

Essential-Characteristic

Category

The

essential-characteristic

category

contains

those

characteristics

that

contribute

to

user

dissatisfaction

if

absent

or

inadequately

provided

The

presence

of

a

privacy

statement

and

disclaimer

although

it

appears

not

to

be

required

for

the

functioning

of

a

Web

site

wasreported

to

be

essential

in

a

Web-user

interface

study

-LSB-

-RSB-

The

correlation

between

the

raters

ranged

from

for

characteristics

-LRB-

presence

of

phone

number

or

mailing

address

and

presence

of

material

in

video

or

audio

format

-RRB-

to

for

indication

of

sponsorship

The

median

correlation

was

for

the

characteristics

evaluated

by

both

raters

In

the

essential

category

sites

-LRB-

-RRB-

contained

a

site-search

feature

and

sites

-LRB-

-RRB-

contained

links

for

navigation

in

the

site

However

sites

contained

neither

of

the

features

Over

half

of

the

sites

contained

either

a

privacy

statement

-LRB-

-RRB-

or

a

disclaimer

-LRB-

-RRB-

but

only

a

third

of

the

sites

contained

both

About

one-third

of

the

sites

have

readability

below

eighth-grade

school

level

and

they

ranked

significantly

higher

-LRB-

tau

P

-RRB-

than

those

that

have

readability

above

or

equal

to

that

level

The

median

grade

level

was

Half

the

sites

contained

one

or

more

broken

internal

or

external

hyperlinks

Enhancement-Characteristic

Category

In

the

enhancement-characteristic

category

sites

-LRB-

-RRB-

indicated

their

sponsorship

Apparently

because

most

of

the

sites

were

sponsored

by

organizations

government

bodies

or

educational

institutions

only

sites

-LRB-

-RRB-

had

either

pop-up

advertisements

or

in-page

banner

advertisements

E-mail

address

-LRB-

-RRB-

was

the

most-common

contact

information

available

while

phone

number

or

mailing

address

was

present

in

of

the

sites

Sites

that

ranked

higher

were

significantly

associated

with

the

presence

of

e-mail

address

for

contact

-LRB-

tau

P

-RRB-

Eleven

sites

-LRB-

-RRB-

had

information

on

behavioral

approach

as

a

method

of

smoking

cessation

Ten

sites

-LRB-

-RRB-

had

information

on

a

medication

-LRB-

nicotine

replacement

-RRB-

approach

and

sites

-LRB-

-RRB-

had

information

on

alternative

approaches

such

as

acupuncture

hypnosis

laser

therapy

and

herbal

cigarettes

Both

the

presence

of

medication

-LRB-

tau

P

-RRB-

and

alternative

approaches

-LRB-

tau

P

-RRB-

were

significantly

associated

with

a

higher

search

ranking

Five

sites

provided

annotated

hyperlinks

to

external

sites

and

their

presence

was

significantly

associated

with

a

higher

search

ranking

-LRB-

tau

P

-RRB-

Eight

sites

contained

interactive

components

such

as

quizzes

games

or

bulletin

boards

Only

site

provided

material

in

video

or

audio

format

Table

Type

of

Web

sites

found

with

different

search

terms

using

Google

search

site

Type

of

Web

Site

Search

Terms

Used

teen

quit

smoking

teen

stop

smoking

teen

smoking

cessation

youth

quit

smoking

adolescent

quit

smoking

Site

with

information

to

help

teenagers

quit

smoking

Page

with

hyperlinks

to

Web

sites

with

information

to

help

teenagers

quit

smoking

News

or

press

release

Report

of

study

results

or

proceedings

from

conferences

Recruitment

of

study

subjects

Commercial

site

-LRB-

were

redirects

-RRB-

-LRB-

was

a

redirect

-RRB-

-LRB-

both

redirects

-RRB-

Site

for

teenagers

but

not

on

smoking

Resources

on

teenager

smoking

cessation

for

parents

or

health

professionals

Health

organizations

or

community

centers

Page

not

found

Other

-LRB-

alt.support.stop-smoking

Usenet

archive

-RRB-

-LRB-

porno-graphic

Web

site

-RRB-

-LRB-

mental

health

Web

site

-RRB-

The

visitor

was

automatically

sent

to

a

page

other

than

the

page

listed

in

the

search

results

-LRB-

see

Discussion

for

details

-RRB-

Technical-Characteristic

Category

In

the

technical-characteristic

category

the

largest

file

size

of

the

landing

page

-LRB-

the

page

reached

when

clicking

on

the

search-site

result

-RRB-

was

kilobytes

which

is

equivalent

to

approximately

seconds

of

download

time

on

a

Kbps

modem

Sites

that

were

equal

to

or

larger

than

kilobytes

-LRB-

-RRB-

were

ranked

significantly

higher

-LRB-

tau

P

-RRB-

by

the

search

sites

Eight

-LRB-

-RRB-

and

-LRB-

-RRB-

of

the

sites

had

meta

description

and

meta

keywords

tags

respectively

The

presence

of

a

meta

description

tag

was

significantly

associated

with

a

higher

search

rank

-LRB-

tau

P

-RRB-

Although

sites

used

cookies

-LRB-

small

files

sent

to

the

browser

along

with

a

Web

page

for

tracking

a

visit

-RRB-

only

of

them

used

a

persistent

cookie

that

is

stored

on

the

user

's

hard

disk

and

used

a

session

cookie

that

is

automatically

deleted

from

the

browser

's

cache

when

the

browseris

closed

Six

-LRB-

-RRB-

sites

were

just

part

of

larger

Web

sites

containing

information

other

than

smoking

The

median

link

density

of

the

Web

pages

was

and

the

maximum

was

A

higher

link

density

was

significantly

associated

with

a

higher

search

rank

-LRB-

tau

P

-RRB-

Discussion

The

key

finding

of

this

study

was

that

using

simple

search

terms

on

popular

search

sites

to

look

for

information

on

smoking

cessation

for

teenagers

less

than

half

-LRB-

of

-RRB-

of

the

sites

found

were

of

direct

relevance

The

remaining

sites

were

study

reports

news

and

hyperlinks

We

did

not

include

all

information

retrieved

from

Web

searches

as

has

been

done

in

studies

on

other

topics

-LSB-

-RSB-

since

users

tend

not

to

go

beyond

the

first

few

pages

of

search

results

-LSB-

-RSB-

Instead

we

evaluated

only

the

top

search

results

to

mimic

typical

Web

search

behavior

Searching

with

the

terms

teen

quit

smoking

on

popular

search

sites

Edwards

et

al

-LSB-

-RSB-

also

reported

that

only

of

the

potential

hits

were

focused

on

cessation

In

our

study

site

of

pornographic

nature

was

found

when

using

the

search

terms

teen

smoking

cessation

but

no

such

sites

were

found

when

using

the

search

terms

teen

quit

smoking

in

contrast

to

a

previous

report

-LSB-

-RSB-

where

out

of

the

top

sites

were

teen

pornography

sites

Of

public

health

concern

was

the

finding

that

sites

were

commercial

sites

and

of

them

were

linked

back

to

a

single

online

drug

store

using

a

page-redirect

spamming

technique

With

page

redirection

an

optimized

page

with

unique

and

specific

terms

is

submitted

to

search

sites

with

the

single

purpose

of

ranking

high

on

a

specific

topic

However

anyone

clicking

the

link

to

this

page

is

automatically

sent

to

a

real

destination

page

which

often

contains

material

unrelated

to

the

initial

search

terms

For

example

one

site

used

what-happens-to-your-body-when-you-quit-smoking.htm

as

the

name

of

its

Web

page

However

this

page

contains

no

information

on

smoking

cessation

Instead

it

is

a

page

with

a

JavaScript

that

immediately

redirects

visitors

to

an

online

drug

store

Several

important

associations

were

found

between

Web-site

characteristics

and

position

ranking

in

the

top

search

results

These

results

can

be

used

for

optimizing

site

development

in

future

smoking-cessation

Web

sites

Essential-Characteristic

Category

As

an

example

of

how

these

results

can

be

used

of

the

items

in

the

essential-characteristic

category

readability

-LRB-

lower

grade

level

-RRB-

was

associated

with

higher

position

ranking

The

lack

of

search

box

navigational

menu

privacy

statement

or

disclaimer

or

the

presence

of

broken

links

was

not

uncommon

but

their

absence

was

not

associated

with

lower

position

ranking

Enhancement-Characteristic

Category

In

the

enhancement-characteristic

category

presence

of

contact

e-mail

address

medication-cessation

information

alternative-approach

information

and

annotated

external

links

were

associated

with

higher

position

ranking

It

is

surprising

to

find

that

only

site

displayed

a

HONcode

insignia

which

along

with

the

associated

membership

is

an

indication

that

a

site

complies

with

an

code

of

conduct

put

forth

by

Health

on

the

Net

-LSB-

-RSB-

Although

of

young

people

said

that

knowing

who

produced

health

information

is

very

important

to

them

only

of

those

who

looked

up

health

information

online

checked

the

source

the

last

time

they

conducted

a

search

-LSB-

-RSB-

and

it

is

likely

that

fewer

will

check

for

the

authenticity

-LRB-

for

example

verify

the

membership

status

of

a

site

at

the

HON

Web

site

-RRB-

of

any

indications

of

external

recognition

even

if

they

are

present

-LSB-

-RSB-

Technical-Characteristic

Category

In

the

technical-characteristic

category

page

size

that

was

larger

than

kilobytes

presence

of

a

meta

description

tag

and

a

high

link

density

were

associated

with

higher

ranking

The

strong

association

between

site

description

meta

tag

and

ranking

-LRB-

tau

P

-RRB-

suggests

that

such

information

is

relevant

to

the

ranking

algorithms

of

the

search-engines

used

Including

a

concise

description

tag

is

likely

to

be

more

effective

in

improving

search-engine

visibility

than

just

a

comprehensive

keywords

list

In

fact

due

to

high

rate

of

keyword

repetition

and

spam

search

sites

such

as

Google

and

AltaVista

do

not

give

consideration

to

the

keywords

meta

tag

in

their

ranking

-LSB-

-RSB-

As

expected

link

density

is

strongly

associated

with

ranking

-LRB-

tau

P

-RRB-

Search

engines

generally

use

the

number

of

incoming

links

-LRB-

link

density

-RRB-

in

their

ranking

algorithm

However

Google

's

PageRank

algorithm

also

takes

into

account

the

number

of

outgoing

links

on

the

page

of

each

of

the

incoming

links

-LSB-

-RSB-

Therefore

to

achieve

a

high

ranking

a

Web

site

should

try

to

get

listed

on

as

many

sites

as

possible

and

in

particular

on

those

sites

that

have

as

few

external

links

as

possible

Since

search

engines

assign

higher

ranking

to

sites

with

incoming

links

that

originate

from

pages

containing

fewer

external

links

and

sites

with

annotated

external

links

tend

to

have

fewer

links

than

those

sites

without

annotated

external

links

this

may

explain

the

association

between

the

presence

of

annotated

external

links

and

higher

ranking

-LRB-

tau

P

-RRB-

To

improve

search

efficiency

users

may

want

to

supplement

results

from

search

sites

with

those

from

subject-based

Web

directories

that

are

created

and

maintained

by

people

rather

than

by

algorithms

such

as

Yahoo!

Directory

which

has

a

teen-smoking

section

-LSB-

-RSB-

Using

the

Yahoo!

directory

we

found

sites

listed

of

which

only

were

found

using

our

search

terms

at

the

popular

search

sites

In

addition

users

may

want

to

learn

and

apply

the

specific

syntax

of

their

favorite

search

sites

when

searching

for

information

For

example

quit-smoking

Web

sites

of

the

commercial

-LRB-

com

-RRB-

domain

can

be

eliminated

from

the

search

results

by

entering

quit

smoking

site

com

in

the

search

box

in

Google

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O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

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