'Expanded' Prader-Willi syndrome in a boy with an unusual 15q chromosome deletion.

A male infant showed features of the Prader-Willi syndrome (including profound hypotonia, cryptorchidism, and mildly dysmorphic facial appearance) but also had additional multiple malformations (congenital heart disease, unilateral renal malmigration, and bifid uvula). A deletion of the long arm of chromosome 15, larger than that usually demonstrated in children with Prader-Willi syndrome, was found. The cytogenetic findings suggest that the infant's hypotonia and cryptorchidism are explicable on the basis of the portion of the deletion usually associated with Prader-Willi syndrome (q11 to q12) but that his other features could be secondary to effects of the more distal region of the deleted segment (q13 to q15).