PKS is caused by an sSMC that consists of two copies or, less commonly, four copies of the genetic material in the p arm of chromosome 12. Recent studies in two individuals with PKS found their sSMCs consisted specifically of genetic material located in a stretch of chromosome 12 's p arm starting at its band 11 and running to its end. This area, called the PKS critical region, contains three genes, ING4, CHD4, and MFAP5 (also termed the MAGP2 gene), which are candidates for contributing to the development of the syndrome. One suggested mechanism for the development of the sSMC in PKS involves three sequential events: 1) chromosome 12 suffers a nondisjunction, i.e. a failure of its homologous chromosomes or sister chromatids to separate properly during the second meiosis cell division that forms maternal eggs; 2) while most of the eggs suffering this nondisjunction die, a rare egg with the nondisjunction acquires a second structural aberration, isochromosome formation, that results in the creation of an extra chromosome consisting of copies of two or four p arms but no q arms of chromosome 12, i.e. the sSMC; and 3) the sSMC-contianing egg, after being fertilized by a genetically normal sperm, develops into an offspring containing copies of this sSMC in some but not all cells, tissues, and/or organs consequently have some but not all of the defects associated with PKS. This mechanism applies only to female parents who are by far the most common originators of the sSMC in PKS. The mechanism explaining the few cases in which male parents form a sperm containing this sSMC has not yet been clearly formulated.
Pallister–Killian syndrome
Hapnes Boman Skeie syndrome
Scheie syndrome
Catel–Manzke syndrome
Gerstmann–Sträussler–Scheinker syndrome
Ohtahara syndrome
Cohen syndrome
Cohen-Gibson syndrome