Two families with Xq27.3 fragility, no detectable insert in the FMR-1 gene, mild mental impairment, and absence of the Martin-Bell phenotype

Dennis, Nicholas R., Curtis, Greta, Macpherson, James N. and Jacobs, Patricia A. (1992) Two families with Xq27.3 fragility, no detectable insert in the FMR-1 gene, mild mental impairment, and absence of the Martin-Bell phenotype. American Journal of Medical Genetics. Part B: Neuropsychiatric Genetics, 43 (1-2), 232-236. (doi:10.1002/ajmg.1320430137).

Abstract

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

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