Pallister-Killian syndrome: Multiband FISH of tetrasomy 12p

Two patients with mosaicism for tetrasomy 12p are described. One was diagnosed at the age of 14 years with severe mental retardation and other dysmorphologic findings and abnormal skin pigmentation. Chromosome analysis of a blood sample showed a normal female karyotype. A skin biopsy specimen showed mosaicism for a marker chromosome. The other patient was diagnosed prenatally, from a chorionic villus sample, but only in the direct preparation. Mosaicism for a marker chromosome was demonstrated. The ultrasound examination revealed no abnormalities. Multicolor and multiband fluorescence in situ hybridization analyses showed that the marker chromosome was derived from chromosome 12p, which confirmed the diagnosis of Pallister-Killian syndrome in both patients. To our knowledge, this is the first report of the use of these fluorescence in situ hybridization techniques in Pallister-Killian syndrome whereby the nature of the marker chromosome could be confirmed to be derived from chromosome 12p.