Population incidence and segregation ratios in the Martin-Bell syndrome.

A clinical and cytogenetic study of children attending schools for the educationally handicapped has been carried out in the City of Coventry. As a result of this an estimate of the population incidence of the Martin-Bell syndrome among schoolchildren has been made. Among school-boys the incidence of mental retardation due to the fra (X) was found to be 0.73 per 1000 and among schoolgirls 0.48 per 1000. The overall prevalence is 0.61 per 1000. Genetic and cytogenetic analysis of 14 families ascertained in an unbiased manner showed that the expected 50% ratio of affected to unaffected relatives was disturbed, the possible result of a segregation distortion.