X-linked recessively inherited non-specific mental retardation. Report of a large family.

A large kindred is described in which 22 males and 3 females show non-specific mental retardation with impaired speech. An X-linked recessive is the most likely mode of inheritance of this condition. Similar families have been described in the literature, characteristic physical abnormalities are absent and performance I.Q. tends to be higher than verbal I.Q. This possible heterogenous condition may be a major individual cause of mental deficiency in males, and may account for the excess of male retardates in the population.