Pallister-Killian Syndrome (PKS) as a Cause of Mental Retardation.

Pallister-Killian syndrome (PKS; OMIM: # 601803) is a rare sporadic syndrome of multiple congenital anomalies attributable to the presence of a de novo mosaic supernumerary isochromosome 12p [i(12p)]. The syndrome presents with a recognizable pattern of findings including: pigmentary skin changes, characteristic facial features (sparse anterior scalp hair, flattened midface, macrostomia, and coarsening of the facial features), and developmental delay. The developmental phenotype of PKS is quite variable, but most are considered to fall into the profound range of developmental retardation. We report on two individuals with classical features of PKS. Notably, in one child the neuropsychological development was significantly more favourable than commonly reported in the literature. This illustrates the loose correlation between geno- and phenotype in PKS.