Genetic evidence that lower circulating FSH levels lengthen menstrual cycle, increase age at menopause, and impact reproductive health: a UK Biobank study

Study question: How does a genetic variant altering follicle stimulating hormone (FSH) levels, which we identified as associated with length of menstrual cycle, more widely impact reproductive health? Summary answer: The T allele of the FSHB promoter polymorphism (rs10835638) results in longer menstrual cycles and later menopause and, while having detrimental effects on fertility, is protective against endometriosis. What is known already: The FSHB promoter polymorphism (rs10835638) affects levels of FSHB transcription and, as a result, levels of FSH. FSH is required for normal fertility and genetic variants at the FSHB locus are associated with age at menopause and polycystic ovary syndrome (PCOS). Study design, size, duration: We conducted a genetic association study using cross-sectional data from the UK Biobank. Participants/materials, setting, methods: We included white British individuals aged 40-69 years in 2006-2010, included in the May 2015 release of genetic data from UK Biobank. We conducted a genome-wide association study (GWAS) in 9,534 individuals to identify genetic variants associated with length of menstrual cycle. We tested the FSH lowering T allele of the FSHB promoter polymorphism (rs10835638) for associations with 29 reproductive phenotypes in up to 63,350 individuals. Main results and the role of chance: In the GWAS for menstrual cycle length, only variants near the FSHB gene reached genome-wide significance (P-8). The FSH-lowering T allele of the FSHB promoter polymorphism (rs10835638G>T; MAF 0.16) was associated with longer menstrual cycles (0.16 s.d. (approx. 1 day) per minor allele; 95% CI 0.12-0.20; P=6×10-16), later age at menopause (0.13 years per minor allele; 95% CI 0.04-0.22; P=5.7×10-3), greater female nulliparity (OR=1.06; 95% CI 1.02-1.11; P=4.8×10-3) and lower risk of endometriosis (OR=0.79; 95% CI 0.69-0.90; P=4.1×10-4). The FSH-lowering T allele was not associated more generally with other reproductive illnesses or conditions and we did not replicate associations with male infertility or PCOS. Limitations, reasons for caution: The data included might be affected by recall bias. Women with a cycle length recorded were aged over 40 and were approaching menopause, however we did not find evidence that this affected the results. Many of the illnesses had relatively small sample sizes and so we may have been under-powered to detect an effect. Wider implications of the findings: We found a strong novel association between a genetic variant that lowers FSH levels and longer menstrual cycles, at a locus previously robustly associated with age at menopause. The variant was also associated with nulliparity and endometriosis risk. We conclude that lifetime differences in circulating levels of FSH between individuals can influence menstrual cycle length and a range of reproductive outcomes, including menopause timing, infertility, endometriosis and PCOS.