The FMR1 premutation as a cause of premature ovarian failure in Brazilian women

ABSTRACT

The loss-of-function mutation of the FMR1 gene due to expansion of the 5' UTR CGG repeat causes the fragile X syndrome, the most frequent form of inherited mental retardation. On the other hand, the FMR1 premutation, which is transcriptionally active and produces the protein, confers an increased risk for premature ovarian failure (POF) to carrier females. Among 41 unrelated Brazilian women with idiopathic POF, we found three carriers of premutations (CGG expansionse > 59 repeats) and two carriers of high-intermediate alleles (50-55 repeats). Two premutations and two intermediate alleles were detected among the 16 familial POF cases, and one premutated woman, among the 25 sporadic cases. The premutation frequency among the familial cases (12.5 percent) differed significantly from that found in a control group of 96 unrelated Brazilian women aged > 47 years, who had not experience POF and in which no premutations or high-intermediate alleles were detected. In the search for factors influencing the probability of a premutation carrier presenting POF, another 20 unrelated premutated women with POF, from fragile X families, were included in the study. The analysis of the FMR1-linked loci DXS548 and FRAXAC1 did not indicate any association of a particular haplotype with the occurrence of POF. An effect of X-inactivation skewing was not apparent in blood cells, and POF-associated premutations showed a wide range of repeat sizes, from 59, the smallest known to expand to full mutations upon transmission to offspring, to approximately 200.