Prader-Willi syndrome associated with an interstitial deletion of chromosome 15

The Prader-Willi syndrome is characterized at birth by marked hypotonia, inactivity, feeding difficulties and abnormal temperature regulation. The diagnosis often is unrecognized until poor feeding is replaced by hyperphagia, leading to obesity in the first several years of life. Developmental delay and mental retardation become apparent during this period as well. These clinical features and their natural progression form the basis for diagnosis. Because many of the clinical features occur in other conditions of infancy and early childhood and because expression in PWS is variable, early diagnosis of the syndrome is often difficult and tentative. Recently, however, detection of cytogenetic abnormalities, particularly an interstitial deletion of a specific region of chromome 15, has added a new dimension to diagnosis and insight to etiology. The young man reported here illustrates the utility of high-resolution cytogenetic analysis in the diagnosis and family counseling of PWS.