title: Additional evidence for fragile X activity in heterozygous carriers.
abstract: The result of a previous study showing an association between mental development and fragile X activity in heterozygous females is given further support by similar investigations of three additional kindreds. The increased frequency of demonstrable fragile X chromosomes in mentally retarded females appears to be due to an increase in the active fragile X while the inactive marker X remains at a similar low frequency in all heterozygotes whether retarded or not. The frequencies of the active fragile X separated the normal and abnormal subjects into two distinct populations. The suggested inverse correlation between the number of lymphocytes with detectable fragile X chromosomes and advancing age can be attributed to ascertainment biases.
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002648:Child; D004303:Dosage Compensation, Genetic; D005260:Female; D005600:Fragile X Syndrome / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D007360:Intelligence; D008297:Male; D008875:Middle Aged; D009864:Ontario; D010375:Pedigree; D012729:Sex Chromosome Aberrations / Q000235:genetics*; D012737:Sex Factors