FRAXA locus in fragile X diagnosis: family studies, prenatal diagnosis, and diagnosis of sporadic cases of mental retardation.
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.[1]References
- FRAXA locus in fragile X diagnosis: family studies, prenatal diagnosis, and diagnosis of sporadic cases of mental retardation. von Koskull, H., Gahmberg, N., Salonen, R., Salo, A., Peippo, M. Am. J. Med. Genet. (1994) [Pubmed]
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