Cytogenetic study of a severe case of Pallister-Killian syndrome using fluorescence in situ hybridization.

Usually, the supernumerary isochromosome 12p characterizing Pallister-Killian syndrome patients was detected in cultured skin fibroblasts but not in cultured blood lymphocytes. The proband of this study was a one-day-old female, who presented with major clinical characteristics of the Pallister-Killian syndrome, and had severe malformations in the form of anal atresia, cleft palate, and severe laryngomalacia. Chromosome preparations from cultured blood lymphocytes and skin fibroblasts, as well as buccal smears, from this patient were analyzed by fluorescence in situ hybridization (FISH) using a chromosome 12-specific alpha satellite probe. The proportions of cells showing positive signals for i(12p) in these samples were found to be 20, 62.5, and 70%, respectively. Repeated FISH studies of buccal smears from this patient showed considerable decreases in the proportions of i(12p) containing cells to 40% at one year of age and to 32% at the age of one year and five months. The decline in the percentage of i(12p)-containing cells in buccal smears with aging supports the concept of in vivo loss of the marker during repeated cell division.