# Handbook of Genetic Counseling/Bardet-Biedl Syndrome-2

Bardet-Biedl Syndrome

## Genetic Etiology

* Mode of inheritance: Autosomal Recessive. It requires a recessive mutation in one of six loci plus an additional mutation in a second locus, known as triallelic inheritance.
* Chromosome locations: This syndrome is linked to 6 different loci-BBS1 on 11q13, BBS2 on 16q21, BBS3 on 3p13, BBS4 on 15q22.3, BBS5 on 2q31, and BBS6 on 20p12
Incidence and Carrier Frequency
* Incidence is 1 in 100,000, with an increased prevalence in Arab and Bedouin populations (1 in 13,500). Carrier frequency is 1 in 179.

## Clinical Features

* Obesity
* Eye Problems: Rod-cone dystrophy (major)
** Retinitis pigmentosa
** Strabismus
** Cataracts
* Mouth and Tooth Problems: High arched palate
** Dental crowding
** Hypodontia
** Small tooth roots
* Cardiac Problems: Left ventricular hypertrophy
** Other congenital heart defects
** Hypertension
* Hepatic Fibrosis
* Hirschsprung disease (less than 10% of patients)
* Hypogonadism (major)
* Undescended testes (10%)
* Hypothyroidism
* Asthma (27%)
* Renal Problems (major): Nephrogenic diabetes insipidus
** Irregular kidney contour (fetal lobulation)
** Polydipsia and Polyuria (66% of patients)
** Recurrent urinary tract infections (30% of patients)
* Polydactyly of hands and/or feet (major)
* Brachydactyly of hands
* Speech delays
* Ataxia
* Developmental delay
* Learning disabilities (major)
* Diabetes mellitus (15-45% of patients)
* A clinical diagnosis is made with the presence of 4 major features or 3 major and 2 minor features
* Age of onset is usually early childhood.
* Life span is variable, depending on severity and management of symptoms.
Testing
* Chromosomal testing is available. This can be done prenatally as well as postnatally.

## Surveillance, Management, and Treatment Options

* In the clinic, fundoscopic examination of the eyes should be performed through dilated pupils as well as blood pressure measurement and urinalysis for glucose, protein and leukocytes. Baseline investigations should include ERG/VER, ECG, echocardiogram, ultrasound of the kidneys and urinary tract and either an IVP or DMSA/DPTA scan. The child should be evaluated by cardiology, ophthalmology, urology, nephrology, genetics, speech, endocrinology, and orthopedics. It is not possible to cure this condition, but regular follow-up for symptoms can improve quality of life.

## Psychosocial Issues

* Guilt, fear, anger, anxiety, sadness, desperation, and depression are common feelings associated with this diagnosis. It is important to assess the family situation, support system, financial position, and living environment as well as offer any resources to families that may be helpful

## Support Groups

* Retinitis Pigmentosa International
    23241 Ventura Boulevard
    Woodland Hills CA 91364
    8189920500
    8003444877
    e-mail: rpint@pacbell.net
    Home Page:
* American Foundation for the Blind
    11 Penn Plaza
    New York NY 10001
    2125027600
    8002325463
    e-mail: afbinfo@afb.org
    Home Page:
* American Printing House for the Blind
    1839 Frankfort Avenue
    Louisville KY 40206-0085
    5028952405
    8002231839
    e-mail: info@aph.org
    Home Page:
* National Association for Parents of the Visually Impaired
    P.O. Box 317
    Watertown MA 02472
    6179727441
    8005626265
    e-mail: napvi@perkins.pvt.k12.ma.us
    Home Page:
* Prevent Blindness America
    500 East Remington Road
    Schaumberg IL 60173
    8478432020
    8003312020
    e-mail: info@preventblindness.org
    Home Page:
* Vision Community Services
    23 A Elm St
    Watertown MA 02472
    6179264232
    8008523029
    e-mail: mablind@tiac.net
    Home Page:
* Blind Children's Fund
    4740 Okemos Road
    Okemos MI 48864-1637
    5173471357
    n/a
    e-mail: blindchfnd@aol.com
    Home Page:
* Laurence Moon Bardet Biedl Syndrome
    c/o The Foundation Fighting Blindness
    Hunt Valley MD 21031
    4107851414
    8883943937
    e-mail: randerson@blindness.org
    Home Page:
* American Council of the Blind, Inc.
    1155 15th Street
    Washington DC 20005
    2024675081
    8004248666
    e-mail: info@acb.org
    Home Page:
* National Association for Visually Handicapped
    22 West 21st Street
    New York NY 10010
    2128893141
    n/a
    e-mail: staff@navh.org
    Home Page: