Pallister-Killian syndrome (PKS) is a very rare chromosomal condition. A chromosome is a thread-like structure (divided into a short arm and a long arm) which is present in the nucleus of all body cells. The chromosomes carry the genes which are the instructions about how to make a new baby from a sperm and an egg. Usually individuals have twenty-three pairs of chromosomes (forty-six chromosomes in each cell). Individuals with PKS have an extra chromosome made up of material from the twelfth pair of chromosomes in some cells. This means there are forty-seven chromosomes in these cells rather than forty-six. The extra chromosome comprises two short arms of chromosome 12 (often referred to as isochromosome 12p). Because the affected person has extra genes, this causes the distinct features associated with PKS. The extra isochromosome 12 is not present in all body cells but only in part of them, with the other cells having a normal chromosome number. The condition is therefore described as a mosaic. It makes the diagnosis of PKS frequently difficult as the extra isochromosome is usually not present in blood cells. The extent to which an individual is affected by PKS depends in part upon the proportion of cells containing the isochromosome 12p throughout the body.

PKS affects both males and females equally. The condition is present at birth and the oldest known individuals with PKS are in their forties.

The major symptoms of PKS include a characteristic facial appearance, learning difficulties, seizures (see entry, epilepsy), loss of muscle tone (hypotonia) and streaks of skin in which there is no colour (hypopigmentation) or darker skin colour than normal (hyperpigmentation) anywhere on the body. Individuals may show some or all of these features and, in addition, may be differently affected in the severity of their symptoms.

Typically individuals with PKS have a high forehead, sparse hair on the temple region of the scalp and eyebrows, an abnormally wide space between the eyes, a fold of skin over the inner corner of the eyes and a flat nose.

At birth infants with PKS are profoundly hypotonic (floppy) and this may persist into later life. Between the ages of five to ten years, children may have stiffness of joints (contractures). Children are almost always developmentally delayed with learning difficulties and minimal speech. Seizures may occur during infancy. Difficulties with vision (see entry, visual impairment) and hearing (see entry, deafness) may also occur. Affected individuals usually have to go to special schools and may not be able to live independently as adults.

A number of other features may be associated with PKS including congenital heart defects, gastro-oesophageal reflux (see entry, Gut Motility Disorders), cataracts and extra nipples. Diaphragmatic problems may occur in newborn babies with PKS, and in these cases babies may die shortly after birth, although some cases can be treated with operations. Because PKS is rare, it is not easily diagnosed.

Inheritance patterns
PKS occurs sporadically. In other words, no other family member, brother and sister, is usually affected.

Prenatal diagnosis
PKS is sometimes suggested by ultrasound examination if major malformations are present or by examination of chorionic villus sampling (CVS) or amniotic fluid.

Medical text written September 2002 by Contact a Family. Approved July 2002 by Professor R Hennekam. Last updated July 2007 by, Professor R Hennekam , Professor in Clinical Genetics and Dysmorphology, Institute of Child Health, London, UK.

Further Online Resources
Medical texts in The Contact a Family Directory are designed to give a short, clear description of specific conditions and rare disorders. More extensive information on this condition can be found on a range of reliable, validated web sites and links to them are included in the CD-ROM version of this Directory. Further information on these resources can be found in our Medical Information on the Internet article.

Support and advice for Pallister-Killian syndrome is available from Unique, the Rare Chromosome Support Group (see entry, Chromosome Disorders)

Currently Contact a Family is actively involved in facilitating the formation of UK condition specific support groups. If you would like to know more about this, please contact the Rare Disorders Team on 020 7608 8700 or e-mail: specific-cond@cafamily.org.uk We look forward to hearing from you.