PALLISTER-KILLIAN SYNDROME IN OLDER CHILDREN AND ADOLESCENTS

The Pallister-Killian syndrome is caused by a mosaic tetrasomy of the short arm of chromosome 12. Although analysis of peripheral blood lymp hocytes usually reveals a normal karyotype, an isochromosome 12p mosai cism is detectable in fibroblast cultures; therefore, in this rare chr omosomal aberration, clinical recognition is crucial for appropriate c ytogenetic investigations. The phenotype of younger children has alrea dy been well documented. During childhood and adolescence, however, th e phenotype changes markedly. The disorder in older children and young adults is characterized by a coarse and flat facies, macroglossia pro gnathia, everted lower lip, and severe psychomotor retardation with mu scular hypertonia and contractures. Two severely mentally retarded pat ients are reported whose diagnoses were confirmed by fibroblast cultur es at ages 16 and 21 years.