Familial Prader-Willi syndrome with apparently normal chromosomes.

We report on 4 sibs (2F, 2M) with Prader-Willi syndrome (PWS). Diagnosis was made clinically on the basis of history, behavior, and physical findings in 3 of the sibs. The other child had died at age 10 months with a history and clinical findings typical of first phase of PWS. Results of chromosome studies on the parents and surviving sibs were normal. The implications of this unusual familial occurrence for our understanding of PWS are discussed.