Pallister-Killian Syndrome Health Article

Definition

Pallister-Killian syndrome (PKS) is a rare chromosome abnormality in which a person has four copies of the short arm of chromosome 12 instead of the normal two copies. Affected individuals have unusual facial features, mental retardation, seizures, patchy color differences in the skin, and various other physical abnormalities. Many fetuses with Pallister-Killian syndrome die during pregnancy or soon after birth.

Description

Pallister-Killian syndrome was first described in 1977. The first two patients Pallister reported were adults with severe mental retardation, unusual facial features, severe lack of muscle strength, and pale areas on their skin. In 1981, Killian and Teschler-Nicola described a child with mental retardation, unusual facial features, pale skin on the face, and absence of hair at the front of the scalp.

Pallister-Killian syndrome may also be called Killian syndrome, Killian/Teschler-Nicola syndrome, Pallister mosaic syndrome, or Teschler-Nicola/Killian syndrome. This syndrome may also be called tetrasomy 12p mosaicism syndrome or isochromosome 12p syndrome based on the characteristic chromosome abnormality detected via laboratory studies. Pallister-Killian syndrome is called mosaic because the characteristic chromosome abnormality that causes the syndrome appears only in a fraction of the total cells examined.

Genetic profile

Pallister-Killian syndrome is a sporadic disorder, which means that it appears to occur at random. The chromosome problem that causes PKS, tetrasomy 12p, does not appear to run in families. Pallister-Killian syndrome is not specifically associated with any specific chemical or environmental exposures.

Tetrasomy 12p is characterized by the presence of four copies of the short arm of chromosome 12, instead of the normal two copies. This chromosome abnormality is not found throughout an affected person's body. Chromosome analysis performed on the blood of persons with Pallister-Killian syndrome virtually always shows normal results. The characteristic chromosome abnormality can, however, be detected via chromosome analysis on skin cells. Through chromosome analysis, tetrasomy 12p is identified due to the presence of what appears to be an extra chromosome composed of two copies of the short arm of chromosome 12. This chromosome composed of two copies of the short arm of chromosome 12 is called an isochromosome. In tetrasomy 12p, there is a total of four copies of the short arm of chromosome 12: there are the two normal copies, plus the two abnormal copies located on the extra isochromosome.