The female and the Fragile X. A study of 144 obligate female carriers

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Abstract
In the present report we summarize our data on 144 obligate female carriers. The clinical and cytogenetic data are reviewed and discussed. 1 In more than 30 % of heterozygotes mental development is borderline to subnormal, and they may also present psychiatric disturbances of which psychotic behaviour is the most frequent. 2 Partial phenotypic expression is present in 28 % of the carriers, and is more frequent in the mentally subnormal. 3 Repeated fragile X screening remains negative in more than 50 % of the patients. This results in great difficulties in accurate genetic counseling of the individual female at risk. In all females with partial clinical expression fragile X screening is positive. 4 Fragile X carriers have a high fertility. A fourfold increase in twinning is observed and this may be an indication of a disturbed cortico-hypothalamic-hypophyseal axis.