# Handbook of Genetic Counseling/Pallister-Killian Syndrome

Pallister-Killian Syndrome

## Genetic Etiology

* Tetrasomy 12p (mosaicism)

## Incidence and carrier frequency

* Very rare disorder
* Affects males and females in equal numbers
* >30 cases reported in the literature

## Risk to various family members

* Sporadic inheritance, extremely rare
* No increased recurrence risk

## Clinical features

* Typical findings:
* Hypotonia
* sparse scalp hair
* a high forehead with frontal bossing
* a coarse face
* an abnormally wide space between the eyes
* broad nasal bridge
* highly arched palate
* epicanthal folds
* large ears with lobes that are thick and protrude outward.
* Additional features many include:
* congenital heart defects
* diaphragmatic hernia
* hypopigmentation
* extra nipples
* seizures
* droopy upper eyelids
* strabismus
* contractures
* cognitive delays, speech delays
* mental retardation
* stenosis of the external auditory canal
* abnormal opening in the anus
* hypoplastic lung
* abnormalities of the genitourinary system
* skeletal malformations.

## Testing/Diagnosis

* the chromosome abnormality in Pallister-Killian Mosaic Syndrome is limited to specific cell types
* mechanism and parental origin of the isochromosome 12p can usually not be determined
* diagnosis is usually made from a chromosome study of skin cells (fibroblasts)
* a blood chromosome study usually shows normal chromosomes
* peripheral blood lymphocytes are continually dividing
* they may lose the extra chromosome with their frequent divisions
* fibroblasts normally cycle less frequently, don't lose the extra chromosome
* Other reasons to test skin cells:
* During the 3rd week of fetal development gastrulation determines 3 germ layers
* Ectoderm: gives rise to the epidermis (skin) and central nervous system
* Endoderm: gives rise to the inner lining of the digestive tract and also the linings of tissues that sprout from the digestive tract, such as the respiratory system, liver, and pancreas
* Mesoderm: gives rise to tissues such as bones, muscle, blood, and connective tissue
* If a chromosome error arises after these tissues differentiate, there could be an error in the skin cells that is not present in other tissues that came from other germ layers

## Surveillance, management, and treatment options

* There is no specific therapy for individuals with Pallister-Killian Syndrome
* Because of poor prognosis, generally only supportive care
* Affected children may benefit from early intervention programs and special education

## Differential diagnoses

* Fryns syndrome

## Psychosocial issues

* Grief over loss of "normal baby"
* Shock over unexpected problems
* Worry about prognosis
* Uncertainty about testing and procedures
* Financial considerations, what will treatment cost?
* Who is their support network?
* Effects on relationships (parent/child)
* Concern about telling other family members
* Future reproductive decisions
* Possible disruption of marital relationships or family dynamics

## Support groups

* PKS Kids
    PO Box 94
    Florissant, MO 63032-0094
    email: gpeters@pkskids.net
    Home page: http://www.pkskids.net
* UNIQUE - Rare Chromosome Disorder Support Group
    P.O. Box 2189
    Surrey Intl CR3 5GN
    Phone #: 4401883 330766
    800 #:
    e-mail: info@rarechromo.org
    Home page: http://www.rarechromo.org

## Sources

* National Organization of Rare Diseases http://www.rarediseases.org
* Bianchi, D., Crombleholme, T., and D'Alton, M. Fetology: Diagnosis and Management of the Fetal Patient. New York: McGraw-Hill, 2000.

## Notes

The information in this outline was last updated in May 2004.