Normal male carriers in the fra(X) form of X-linked mental retardation (Martin-Bell syndrome).
Evidence for the transmission of X-linked mental retardation through normal male carriers is reviewed in 6 kindreds. In these pedigrees we identified 15 unaffected males who likely had passed the gene on through their daughters. Fifty-one mentally retarded grandsons or great grandsons descended from these male carriers. In total, these males had 50 daughters with only 2 of them being of low intelligence. Two of the male carriers were recently identified through fra(X)- positive results in their mentally normal daughters. Among the sibs of these males, mentally retarded brothers were found in 3 families. This was unexpected since earlier observations suggested that the risk for mental retardation among sibs of nonmanifesting carriers is exceedingly low.
D005260:Female; D005600:Fragile X Syndrome / Q000235:genetics* / Q000523:psychology; D006579:Heterozygote; D006801:Humans; D008607:Intellectual Disability / Q000235:genetics; D007360:Intelligence; D008297:Male; D010375:Pedigree; D010641:Phenotype; D012306:Risk; D012729:Sex Chromosome Aberrations / Q000235:genetics*