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Purpose The objective of this analysis is to examine the relationship between Fragile X Mental Retardation 1 gene (FMR1) cytosine-guanine-guanine (CGG) repeat number and ovarian reserve, with a particular focus exclusively on the range of CGG repeat number below the premutation (PM) range (<55 CGG repeats). Methods Our study included female patients who underwent assessment of FMR1 CGG repeat number and serum antiMullerian hormone (AMH) in 2009-2014. To examine the association between FMR1 repeat number and serum AMH, we created three summary measures of CGG repeat number for the two alleles-BSum,^BMax,^and BGap^(absolute difference). Using multivariable regression models, controlling for age, we then analyzed the impact of these summary measures on AMH.Results A total of 566 patients were included in our study. Using multivariable regression models, we found that the relationship between CGG repeat number and AMH differed depending on age. Specifically, in younger women, AMH increased by 7-8 % (Sum p<0.01, Max p=0.04) for every 1 unit increase in CGG repeat number. In contrast, starting at age 40, there was a 3 to 5 % decline in AMH for every 1 unit increase in CGG repeat number (Sum p<0.01, Max p=0.04). Conclusions This is the first study to report a statistically significant correlation of ovarian reserve and CGG repeat number in women with <55 CGG repeats. Although these women are generally considered to have a normal phenotype, our data suggest that increasing CGG repeat number within this normal range is associated with a more rapid decline in ovarian reserve.

This is the first study to establish a stem cell model aimed to understand FMR1 CGG repeat instability amongst female PM carriers. Our preliminary data indicate that CGG repeat number, transcription, and translation are conserved upon induction to pluripotency.