Duplication or insertion in 15q11–13 associated with mental retardation ‐short stature and obesity ‐ Prader‐Willi or Cohen syndrome?

Difficulties of differential diagnosis between Prader-Willi Syndrome and Cohen Syndrome are demonstrated in a 12-year-old girl with obesity and mental retardation. Cytogenetic studies showed an apparently supernumerary band on chromosome 15 in the proximal region q11-13. Both parents have a normal karyotype. The aberrant chromosome was derived from an apparently normal paternal chromosome.