rs7910927

rs7910927 is a common intronic variant in JMJD1C on chromosome 10q21.3, and it is the lead marker for the second-strongest known locus influencing circulating sex hormone-binding globulin. A genome-wide meta-analysis of 21,791 people with validation in a further 7,046 (Coviello et al., PLoS Genetics 2012) found it associated with SHBG at p = 6.1e-35, with a similar effect in men and women. Because SHBG is the protein that carries testosterone and estradiol through the bloodstream, this variant also shifts measured total testosterone — but in 178,782 men in the UK Biobank it showed no association whatsoever with bioavailable testosterone (p = 0.66), and in women it moves total and bioavailable testosterone in opposite directions. The practical reading is narrow and specific: this variant can make a total testosterone result sit a little above or below where the active hormone actually is, which is a reason to ask for SHBG and free testosterone on the same panel rather than total testosterone alone. It says nothing about androgen status by itself. All effect sizes above are from European-ancestry cohorts; the one published test in an East Asian population found no association with low testosterone. This variant carries no information about semen quality: in a Danish study of 1,027 young men plus 315 fertile and 252 infertile men (Morup et al., Scientific Reports 2017), JMJD1C genotype showed no association with semen volume, sperm concentration, total sperm count, sperm morphology or sperm motility. Nothing here should be read as bearing on the ability to conceive.