Children with the fragile X chromosome at schools for the mildly mentally retarded.

An investigation of children in schools for the moderately mentally handicapped in Coventry demonstrated that 29 of 259 children had a significant chromosomal abnormality. 10 of 155 boys (6 per cent) and 10 of 104 girls (10 per cent) had the fragile X syndrome. The clinical features which suggested this syndrome in males were IQ in the 50 to 70 range, head circumference greater than the 50th centile and post-pubertal testicular volume greater than the 50th centile. For both males and females, large ears were a useful sign. All children with fragile X had a carrier parent. The occurrence of mental retardation among sibs was one in two for brothers and one in four sisters. Considering all the males with fragile X syndrome resident in Coventry (this and previous studies), there were twice as many in schools for the moderately mentally handicapped as there were in schools for the severely mentally handicapped. There were as many females as males in the schools for the moderately mentally handicapped.