The incidence of nonspecific mental retardation is higher in males than in females, and responsible genes on the X chromosome continue to be identified. Xq28 duplications involving the MECP2 gene have recently been described in male patients with severe mental retardation, infantile hypotonia, progressive spasticity, and recurrent infections, but the frequency of such duplications is unknown. The MECP2 gene is responsible for Rett syndrome, which is a sporadic disease primarily affecting females.
In a cohort of 283 males with unexplained X-linked mental retardation, researchers identified duplications in Xq28 that included the MECP2 gene in about 1% of cases. They also identified MECP2 duplications in 2% of 134 males with severe mental retar…