Prader-Willi syndrome and chromosome 15. A clinical discussion of 20 cases.

A chromosome 15 anomaly was observed in 12 of 20 patients, 17 of whom were clinically suspected of having Prader-Willi syndrome (PWS). The clinical features of eight cases with 15q11-12 deletion were very similar to those originally described in PWS. On the other hand, the group of normal karyotype patients is heterogeneous, and their features do not strictly correspond to the clinical definition of PWS. However, the hypothesis that PWS is associated with deletion of 15q11-12 can neither explain the apparently balanced translocations of chromosome 15 nor account for the small supernumerary metacentric chromosomes corresponding to an isochromosome 15 for band 15q11 observed in some cases.