Genome-Wide Association Study of Estradiol Levels, and the Causal Effect of Estradiol on Bone Mineral Density

ContextEstradiol is the primary female sex hormone and plays an important role for skeletal health in both sexes. Several enzymes are involved in estradiol metabolism but few genome-wide association studies (GWAS) have been performed to characterize the genetic contribution to variation in estrogen levels. ObjectiveIdentify genetic loci affecting estradiol levels and estimate causal effect of estradiol on bone mineral density (BMD). DesignWe performed GWAS for estradiol in males (N = 147,690) and females (N = 163,985) from UK Biobank (UKB). Estradiol was analyzed as a binary phenotype; above/below detection limit (175 pmol/L). We further estimated the causal effect of estradiol on BMD using Mendelian randomization. ResultsWe identified 14 independent loci associated (P<5x10-8) with estradiol levels in males, of which one (CYP3A7) was genome-wide and seven nominally (P<0.05) significant in females. In addition, one female specific locus was identified. Most loci contain functionally relevant genes that have not been discussed in relation to estradiol levels in previous GWAS. For example, SRD5A2, which encodes a steroid 5-alpha reductase that is involved in processing androgens, and UGT3A1 and UGT2B7 which encode enzymes likely to be involved in estradiol elimination. The allele that tags the O blood group, at the ABO locus, was associated with higher estradiol levels. We identified a causal effect of high estradiol levels on increased BMD in both males (P=1.58x10-11) and females (P=7.48x10-6). ConclusionOur findings further support the importance of the bodys own estrogen to maintain skeletal health in males and in females.