[Prader-Willi syndrome in a young infant].

Four children aged 2.5 years, 15.7 and 7 months, including a pair of twins, after birth displayed hypotonia which necessitated tube feeding. Other features were a narrow forehead and a thin triangular upper lip, but these abnormalities were not conspicuous. An extensive supplementary examination for cerebral and muscular disorders initially failed to produce a diagnosis. It was only when the Prader-Willi syndrome was suspected and a corresponding abnormality on chromosome 15 was looked for that this diagnosis could be made. Early diagnosis of this syndrome will avoid further invasive diagnostic procedures and make early treatment possible.