XYY Karyotype in a Mentally Retarded Man with Prognathism and Malformation of His Hands and Toe Nails

We report on a 25-year-old man who was referred for evaluation of possible Fragile X syndrome on the basis of mild mental retardation and malformation of his hands and toe nails. He was found not to have this syndrome but to have a 47, XYY karyotype. Only one other case of XYY syndrome with prognathism and malformation of hands has been reported.