Deletion of chromosome 15 (q11-13) in a Prader-Labhart-Willi syndrome clinic population.

Deletion of the long arm of chromosome 15 has recently been reported in a number of patients with the Prader-Labhart-Willi syndrome who were studied with prometaphase banding. We performed cytogenetic analysis on 12 patients with this disorder in whom the clinical diagnosis was certain. A specific cytogenetic anomaly, del(15q11-13) was found in all of the 12 patients. In nine of the 12, the deletion was noted in all cells examined; in two, there was mosaicism, some cells having the deletion and others being normal; one patient had a 7;15 translocation. No clinical differences were evident between individuals with mosaicism for the translocation and those with the typical deletion in all cells examined. The finding that all of our patients with Prader-Labhart-Willi syndrome have a cytogenetic anomaly, with some patients having mosaicism, distinguishes the results of this study from those of previous reports. Prometaphase chromosome analysis is recommended in all individuals clinically suspected of having Prader-Labhart-Willi syndrome and should be considered in hypotonic infants without a specific diagnosis.