Prader-Willi and Klinefelter syndrome: a coincidence or not?

Prader-Willi syndrome is a complex multisystem disorder characterized by neonatal hypotonia, developmental delay, short stature, obesity, behaviour problems, hypothalamic hypogonadism and characteristic appearance. A number of sex chromosome abnormalities have been reported in children with Prader-Willi syndrome. We report on an infant with a 47, XXY karyotype and Prader-Willi syndrome diagnosed at 2 months of age. He is possibly the youngest to be reported with both Prader-Willi syndrome and Klinefelter syndrome. We have shown that the extra X chromosome causing Klinefelter syndrome is paternal in origin and Prader-Willi syndrome is due to maternal heterodisomy indicating that these two events occurred coincidentally.