Two families with Xq27.3 fragility, no detectable insert in the FMR-1 gene, mild mental impairment, and absence of the Martin-Bell phenotype.
In 2 families, propositi were investigated because of mild developmental delay and, in one case, behavior disorders. Seven males in the 2 families were found to have a fragile site at Xq27.3 but the usual insert in the FMR-1 gene was absent. The affected males had mild, or in some cases, no clear intellectual impairment and did not have the Martin-Bell phenotype. Carrier females in one family tended to show a high level of cytogenetic expression of the fragile site but were clinically normal. It is not yet clear whether these families have unusual mutations in the FMR-1 gene or whether their fragile sites are different, but cytogenetically indistinguishable from, that associated with inserts in the FMR-1 gene.
Dennis
N R
NR
Wessex Regional Clinical Genetics Services, Princess Anne Hospital, Southampton, England.
Curtis
G
G
Macpherson
J N
JN
Jacobs
P A
PA
D000293:Adolescent; D002675:Child, Preschool; D043283:Chromosome Fragile Sites; D002873:Chromosome Fragility; D004252:DNA Mutational Analysis; D005260:Female; D005600:Fragile X Syndrome / Q000235:genetics* / Q000473:pathology / Q000523:psychology; D006579:Heterozygote; D006801:Humans; D007360:Intelligence; D008297:Male; D010375:Pedigree; D010641:Phenotype; D014960:X Chromosome