Risk effect of maternal age in Pallister i(12p) syndrome.

Pallister syndrome is consequent to mosaicism for i(12p). The isochromosome is found mainly in skin fibroblast cultures, but rarely also in cultured peripheral blood lymphocytes. Maternal age for reported cases of Pallister syndrome was significantly older (p less than 0.005) compared to maternal age for the general population, and similar to maternal age in cases of Down syndrome (p less than 0.5). Paternal age in cases of Pallister syndrome was that expected in the general population from the age of their spouses (p less than 0.9). These data complement the maternal age effect seen in other aneuploidy conditions and suggest, as is found in mosaic cases of Down syndrome, that the chromosomally normal cell line in Pallister syndrome arises post-conception from a zygote already aneuploid consequent to meiotic nondisjunction.