Parental origin of the isochromosome 12p in Pallister-Killian syndrome: molecular analysis of one patient and review of the reported cases.

Pallister-Killian syndrome (PKS) is characterized by multiple congenital anomalies including pigmentary skin changes, mental retardation, and the mosaic presence of a tissue-limited isochromosome 12p [i(12p)]. Mechanism(s) of formation and parental origin of the isochromosome are not well understood. In this study, microsatellite DNA markers of chromosome 12p were used to identify the parental origin of the extra chromosome in an 8-year-old previously reported patient with PKS. The i(12p) was found to be maternally inherited. Reported cases of PKS where the parental origin of the i(12p) was determined were also reviewed. In all the cases, with one exception, the errors were found to be maternal in origin. Premeiotic mitotic error may be the most likely mechanism for i(12p) formation in this syndrome.