Ring chromosome 22 resulting in partial monosomy in a mentally retarded boy.

We describe a 7-year-old boy presenting with mental retardation and hyperactivity. Clinical features include microcephaly, hypertelorism, epicanthic eye folds and antimongoloid slant. He also has large ears, large hands and feet, and torticollis. The karyotype was 46, XY, r (22) (p13q13). In situ hybridisation studies with a subtelomeric probe for distal 22q confirmed that the ring was deleted causing partial monosomy of 22q.