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What is PKS?

Pallister-Killian Mosaic Syndrome or PKS is a chromosome abnormality when a tetrasomy of the short arm of chromosome 12 (12p) occurs for no known reason. 

PKS has the following characteristics:

  • low muscle tone

  • facial features that are common to the syndrome-high forehead, broad nasal bridge, wide space between the eyes

  • sparse scalp hair at birth

  • high, arched palate

  • hypopigmentation

  • extra nipples

  • cognitive and developmental delays. Although most PKS children have these delays, many children are only mildly handicapped.

  • diaphragmatic hernias


PKS happens randomly and for no known reason. It is thought that there are fewer than 500 diagnosed cases of PKS in the world, however, doctors at Children's Hospital in Philadelphia believe that the incidence of PKS is much higher! They feel there may be as many as 2,000 cases in the United States alone. So why aren't these numbers reflected? It is likely that there may be this many cases, but they are going undiagnosed. The main cause of these undiagnosed cases is the method of testing. PKS can be diagnosed in utero via amniocentesis, although occasionally, even this has produced a false negative.


After birth, diagnosis is best made by a buccal smear or a skin biopsy.  New array blood testing can be very accurate. The blood cells in the body quickly regenerate and the mosaic cells leave the bloodstream after just a few days, making a diagnosis via bloodwork inconclusive or falsely negative. Ask for a buccal smear if you have any reason to believe your child may have the traits of a syndrome.

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