The fragile X chromosome in a large Indian kindred.

A large Indian kindred in which the fragile X chromosome is segregating has been investigated in Cape Town. Eight male hemizygotes and four female heterozygotes were mentally retarded. There is suggestive evidence that one deceased male of reportedly normal intelligence may have been a hemizygote. The existence of the fragile X syndrome in a number of different ethnic groups supports the contention that the gene controlling the phenotype and the fragile site are the same, or at least overlap.