Clinical, cytogenetic, and molecular observations in a patient with Pallister-Killian-syndrome with an unusual karyotype.

Pallister-Killian syndrome is a clinically recognizable syndrome, usually due to a tissue-limited mosaicism for a supernumary 12p isochromosome (i12p). Here we report an unusual case with tetrasomy/trisomy/disomy 12p mosaic in fibroblasts and trisomy/disomy 12p mosaic in lymphocytes. The tetrasomy 12p was due to an i12p, the trisomy 12p to a single 12p marker. Both marker chromosomes were investigated with conventional cytogenetic techniques and fluorescent in situ hybridization (FISH). Stability under culturing conditions was studied. DNA-analysis revealed prezygotic maternal origin of the extra 12p material. Clinically, the patient seems to have less retardation than most patients with Pallister-Killian syndrome.