FMR1 repeat sizes in the high end of the normal range: no significant association with spontaneous 46,XX primary ovarian insufficiency detected

Abstract

OBJECTIVE: To determine if FMR1 CGG repeat sizes of 35 to 54 (high end of the normal range) are associated with spontaneous 46,XX primary ovarian insufficiency (sPOI). A prior study found such an association (Bretherick et al 2005), yet CGG repeat sizes in this range are not uncommon in controls. This raises significant issues around genetic counseling in women with sPOI and led us to examine our own data in this regard.DESIGN: Cross-sectional.MATERIALS AND METHODS: We recruited 252 women with sPOI between the ages of 18 and 42 years. Southern blot and polymerase chain reaction (PCR) amplification assays were used to determine the size and methylation status of the CGG repeats within the FMR1 gene. The Southern blot assay utilizes the DNA probe StB12.3 and an Eco R1/Nru 1 double digest (Mayo Medical Laboratories). We compared findings to a published healthy control reference group of 161 Canadian women (Bretherick et al 2005). Analysis: Fisher exact test, Spearman correlation, and Wilcoxon rank sum test.RESULTS: We found 45/504 (8.9%, 95% CI 6.6, 11.8) of alleles in the 35 to 54 CGG repeat range in women with sPOI. This was not statistically different from 21/322 (6.5%) in the reference control group (p=0.24). There was a negative correlation of borderline significance between the bi-allelic mean repeat size and age of diagnosis of sPOI (r=-0.12, p=0.051). No such correlation was found using the highest allele repeat size (r=-0.04, p=0.54). Women with primary amenorrhea (22/252, 8.7%) did not differ significantly from other women with sPOI with regard to bi-allelic mean repeat size or the highest allele repeat size (p=0.75 and p=0.33, respectively).CONCLUSIONS: Despite a larger sample size, we were unable to confirm a prior report of an association between FMR1 CGG repeat sizes of 35 to 54 (high end normal range) and sPOI. Further studies are indicated. OBJECTIVE: To determine if FMR1 CGG repeat sizes of 35 to 54 (high end of the normal range) are associated with spontaneous 46,XX primary ovarian insufficiency (sPOI). A prior study found such an association (Bretherick et al 2005), yet CGG repeat sizes in this range are not uncommon in controls. This raises significant issues around genetic counseling in women with sPOI and led us to examine our own data in this regard. DESIGN: Cross-sectional. MATERIALS AND METHODS: We recruited 252 women with sPOI between the ages of 18 and 42 years. Southern blot and polymerase chain reaction (PCR) amplification assays were used to determine the size and methylation status of the CGG repeats within the FMR1 gene. The Southern blot assay utilizes the DNA probe StB12.3 and an Eco R1/Nru 1 double digest (Mayo Medical Laboratories). We compared findings to a published healthy control reference group of 161 Canadian women (Bretherick et al 2005). Analysis: Fisher exact test, Spearman correlation, and Wilcoxon rank sum test. RESULTS: We found 45/504 (8.9%, 95% CI 6.6, 11.8) of alleles in the 35 to 54 CGG repeat range in women with sPOI. This was not statistically different from 21/322 (6.5%) in the reference control group (p=0.24). There was a negative correlation of borderline significance between the bi-allelic mean repeat size and age of diagnosis of sPOI (r=-0.12, p=0.051). No such correlation was found using the highest allele repeat size (r=-0.04, p=0.54). Women with primary amenorrhea (22/252, 8.7%) did not differ significantly from other women with sPOI with regard to bi-allelic mean repeat size or the highest allele repeat size (p=0.75 and p=0.33, respectively). CONCLUSIONS: Despite a larger sample size, we were unable to confirm a prior report of an association between FMR1 CGG repeat sizes of 35 to 54 (high end normal range) and sPOI. Further studies are indicated.