Genetic Susceptibility for Low Testosterone in Men and Its Implications in Biology and Screening: Data from the UK...

Despite strong evidence of heritability, few studies have attempted to unveil the genetic underpinnings of testosterone levels.

To identify testosterone-associated loci in a large study and assess their biological and clinical implications.

The participants were men from the UK Biobank. A two-stage genome-wide association study (GWAS) was first used to identify/validate loci for low testosterone (LowT, <8 nmol/l) in 80% of men (N = 148 902). The cumulative effect of independent LowT risk loci was then evaluated in the remaining 20% of men.

Associations of single nucleotide polymorphisms (SNPs) with LowT were tested using an additive model. Analyses of the expression quantitative trait loci (eQTLs) were performed to assess the associations between significant SNPs and expression of nearby genes (within 1 Mbp). A genetic risk score (GRS) was used to assess the cumulative effect of multiple independent SNPs on LowT risk.

The two-stage GWAS found SNPs in 141 loci of 41 cytobands that were significantly associated with LowT (p < 5 × 10^-8), including 94 novel loci from 38 cytobands. An eQTL analysis of these 141 loci revealed significant associations with RNA expression of 155 genes, including previously implicated (SHBG and JMJD1C) and novel (LIN28B, LCMT2, and ZBTB4) genes. Among the 141 loci, 42 were independently associated with LowT after a multivariable analysis. The GRS based on these 42 loci was significantly associated with LowT risk in independent individuals (N = 37 225, p _trend = 3.16 × 10^-162). The risk ratio for LowT between men in the top and those in the bottom GRS deciles was 4.98-fold. Results are limited in generalizability as only Caucasians were studied.

Identification of the genetic variants associated with LowT may improve our understanding of its etiology and identify high-risk men for LowT screening.

We identified 141 new genetic loci that can be incorporated into a genetic risk score that can potentially identify men with low testosterone.