MENTAL STATUS OF FEMALES WITH AN FMR1 GENE FULL MUTATION

The cloning of the FMR1 gene enables molecular diagnosis in patients a nd in carriers (male and female) of this X-linked mental retardation d isorder. Unlike most X-linked disorders, a considerable proportion of the female carriers of a full mutation in the FMR1 gene is affected. I n this study, the intelligence quotients (IQs) were ascertained by the Wechsler Adult Intelligence Scale in 33 adult females with a full mut ation, with 28 first-degree adult female relatives (mainly sisters) wi thout a full mutation as controls. Seventy-one percent of the females with a full mutation had IQ scores below 85. In paired analysis, no si gnificant correlation could be detected between the IQs of the females with a full mutation and those of their first-degree female relatives , reflecting a dominant effect of the FMR1 gene full mutation in the m ental development of females. Considering females with a full mutation only, we observed a significant relation between the proportion of no rmal FMR1 alleles on the active X chromosome and IQ. We present a mode l to explain this relationship.