Neurologic Aspects of 49,XXXXY Syndrome

49,XXXXY syndrome is a rare sex chromosome aneuploidy syndrome characterized by mental retardation, severe speech impairment, craniofacial abnormalities, multiple skeletal defects, and genital abnormalities. We describe a 13-year-old boy with 49,XXXXY syndrome, language impairment, seizures, and left-hemisphere magnetic resonance imaging abnormalities and review the distinctive neurologic, cognitive, and behavioral phenotypes associa t e d w i t h t h i s d i s o r d e r. F i n a l l y, w e d i s c u s s testosterone supplementation in the treatment of this syndrome. ( J Child Neurol 2003;18:501—504).