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Am J Med Genet. 1994 Jul 15;51(4):486-9.

FRAXA locus in fragile X diagnosis: family studies, prenatal diagnosis, and diagnosis of sporadic cases of mental retardation.

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1
Department of Obstetrics and Gynecology, Helsinki University Hospital, Finland.

Abstract

Three hundred eighty-seven individuals from 32 Finnish fragile X families were studied, using the probe StB12.3 [Oberlé et al., 1991: Science 252:1097-1102] for the FRAXA locus, to reveal length variations in the FMR-1 gene. As expected, the affected individuals (with few exceptions) showed a full mutation; a few affected individuals with a premutation only were found. Seventy percent of the females with a full mutation were affected. The size of the mutation remained unchanged in 6, increased in 73, and decreased in 6 female meioses. In male meioses the size was unchanged in 15 cases, increased in 2 cases, and decreased in 1 case. Prenatal diagnosis was performed in 20 cases. In 7 of these the mutation was inherited by the fetus. Four hundred sixty-four mentally retarded patients were referred to us for FRAXA analysis. In 5% of these the fragile X mutation was found. In addition to the clear cut negative or positive results there were 6 cases in which an increase of 50-80 bp was detected. These findings may represent either large normal alleles or small premutations suggesting a possible tissue mosaicism which could explain the retardation of the patients.

PMID:
7943025
DOI:
10.1002/ajmg.1320510438
[Indexed for MEDLINE]
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