Premature ovarian failure in the fragile X syndrome.

The full mutation leading to the fragile X syndrome is a dynamic trinucleotide repeat located in the 5' untranslated region of the FMR1 gene. The premutation allele contains approximately 60 to 199 repeats, is unstable, and originally not considered detrimental; that is, there did not appear to be a phenotype consequence of the long repeat tract. However, in the late 1980s and early 1990s, preliminary findings suggested that nonimpaired heterozygotes were at risk of early menopause and increased rates of twinning, both indications of ovarian failure. Once premutation carriers could be distinguished from full mutation carriers, this phenotype was found to be restricted to premutation carriers only. Based on the recent studies reviewed here, approximately 21% of premutation carriers have premature ovarian failure (POF) compared to only 1% in the general population, or a relative risk of 21. Moreover, among women with idiopathic sporadic or the more rare form of familial POF, approximately 2% and 14%, respectively, carry the premutation. To date, data supporting increased twinning rates are conflicting and need to be resolved. Neither the underlying cellular pathophysiology of POF caused by the premutation allele nor molecular mechanism underlying the presence of the long repeat tract of the premutation allele is understood. Irrespective, women who carry the premutation allele should have not only genetic counseling but also fertility counseling to ensure that they reach their goals for reproduction.