Clinical variability of tetrasomy 12p.

We describe five patients with tetrasomy 12p (one previously reported). These patients exhibit a very wide range of phenotypic features from that of classic Pallister-Killian syndrome to only mild learning disabilities with pigmentary skin changes. As such, these cases highlight the fact that tetrasomy 12p [i(12p)] and Pallister-Killian syndrome are not synonymous, although this combination of genotype and phenotype is often seen. This information is especially important in prenatally ascertained i(12p). The full spectrum of phenotypic possibilities associated with this chromosome aneuploidy should be discussed in prenatal counseling.