Frequency of Fragile X Premutations in Women With Premature Ovarian Failure: Experience in a Large Molecular Diagnostic Laboratory

Abstract

To compare the number of fragile X premutations identified in women with premature ovarian failure (POF) with the number of premutations detected in females undergoing fragile X analysis for an indication of carrier screening. Retrospective data analysis. This study is a review of fragile X carrier testing results from January 2002 to March 2005. The number of fragile X premutations identified in females with an indication of POF is compared with the number of premutations identified in females with a testing indication of screening. The control group consisted of 14,621 females with no family history suggestive of fragile X syndrome (screening group), while the study population consisted of 88 females with POF. Indications for testing were provided by the referring physician. Clinical details of the POF were not provided. Patients with POF and a family history suggestive of fragile X syndrome were excluded from the study population. Fragile X analysis was performed by EcoR1 and EagI digestion of genomic DNA followed by Southern blot analysis and hybridization with the StB12.3 probe to assess fragile X (FMR1) gene CAG repeat length and methylation status. Precise sizing of repeats up to 120 (CAG)n was determined by PCR amplification of the FMR1 gene using fluorescently labeled primers and separation by capillary electrophoresis, or by blotting and hybridization of the PCR product to a 32P labeled probe. Among the 88 women with premature ovarian failure, 5 had a premutation (55 - 200 repeats) in the FMR1 gene, 2 had an intermediate number of CAG repeats (45-54) and 79 had CAG repeats within the normal range (<45). Two results were suggestive of the presence of only one X chromosome. In the control population, 1 had a full mutation (>200 CAG repeats with abnormal methylation), 65 had a premutation, 325 had an intermediate allele and 14,230 had CAG repeats within the normal range. The premutation carrier frequency among women with POF (1 in 17.6), is higher than the carrier frequency among women with no family history of fragile X (∼1 in 225). Our data are consistent with previous studies, which demonstrate that women with POF are at increased risk of carrying an FMR1 premutation. These RESULTS underscore the importance of offering fragile X carrier testing to women with POF. For those identified with a premutation, genetic counseling is important for the patient, and to identify other at-risk family members. Patients with POF may utilize assisted reproductive technologies (ART), including in vitro fertilization (IVF) to achieve pregnancy. Prior to undergoing IVF, those with a premutation need to be informed that they are at increased risk of having a child with fragile X syndrome, the most common cause of inherited mental retardation. Preimplantation genetic diagnosis (PGD) and use of donor eggs may be options for these patients.