Pallister-Killian syndrome


Pallister-Killian syndrome (PKS) is a rare chromosome disorder, also called tetrasomy isochromosome 12p. Affected individuals display typical facial features as well as developmental delay.


Last updated October 2017 by Professor R Hennekam, Professor in Paediatrics, Academic Medical Centre, Amsterdam, Netherlands.

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What are the symptoms?

The main features include

  • hypotonia (floppiness)
  • a distinctive appearance, with a high, rounded forehead, widely spaced eyes and a large mouth with a thin upper vermillion (lip)
  • streaks or patches of darker (hyperpigmentation) or lighter (hypopigmentation) skin
  • developmental delay (see entry Global Developmental Delay); varies from mild to severe
  • learning difficulties (see entry Learning Disability)
  • epilepsy
  • sparse hair or bald patches around the temples, and sparse eyebrows.

A number of other features may be associated with PKS, including heart defects, gastro-oesophageal reflux, umbilical hernia, missing teeth and hearing and vision problems. Diaphragmatic hernia occurs when there is a hole in the muscle that separates the contents of the abdomen from the chest, so part of the gut may develop in the chest, leaving too little room for the lungs to grow. This occurs more frequently in babies with PKS.

What are the causes?

A chromosome is a thread-like structure that is present in the nucleus of cells. Usually individuals have 23 pairs of chromosomes (46 chromosomes in each cell). Individuals with PKS have an extra chromosome made up of material from the twelfth pair of chromosomes in some cells, so 47 in total. The extra material from chromosome 12 is not present in all body cells, so the condition is described as a mosaic.

How is it diagnosed?

PKS is usually diagnosed after birth. Chromosome studies in a blood sample often produce a normal result in PKS due to mosaicism. Other tissues such as skin or the mucous covering of the inside of the mouth, are more likely to reveal the additional chromosome. Often, a buccal smear (where cells are scraped from the inner side of the cheeks) is taken first, and if this does not give a useful result a skin biopsy is taken.

How is it treated?

There is no cure for the condition. Management involves providing medical support for the features of PKS, as well as appropriate education, emotional and social support. Some babies may be severely affected by diaphragmatic hernia and this may need immediate surgery. Heart defects may also require surgery. Seizures typically need to be controlled with medication. Regular checks of the child will be needed to assess their level of development and vision and hearing. Most (but not all) people will PKS will require care throughout their lives.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
PKS occurs sporadically, meaning no other family member is usually affected.

Prenatal diagnosis
Abnormalities on an ultrasound scan, such as short arms and legs, a diaphragmatic hernia, heart defect or polyhydramnios (too much fluid around the baby) may be observed. A mother can then be offered a chorionic villus sampling test (CVS) test to look for the extra chromosome 12 material.

Is there support?

Information and support in the UK for Pallister-Killian syndrome is provided by Unique (see entry Chromosome disorders).

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