The role of testosterone in chronic kidney disease and kidney function in men and women: a bi-directional Mendelian randomization study in the UK Biobank

Background Chronic kidney disease (CKD) has an apparent sex disparity, with a more rapid progress in men than in women. Whether the well-established sex-specific evolutionary biology trade-off between reproduction and longevity might inform CKD has not previously been considered. Relevant evidence from randomized controlled trials (RCTs) is not available. Methods We used a bi-directional Mendelian randomization study to obtain unconfounded estimates using the UK Biobank. Single nucleotide polymorphisms (SNPs) that strongly (p value < 5 x 10(-8)) predicted testosterone in a sex-specific manner were applied to 179,916 white British men (6016 CKD cases) and 212,079 white British women (5958 CKD cases) to obtain sex-specific associations with CKD, albuminuria, and estimated glomerular filtration rate (eGFR). We also used multivariable MR to control for sex hormone binding globulin (SHBG). For validation, we similarly examined their role in hemoglobin and high-density lipoprotein cholesterol (HDL-c). We also assessed the role of kidney function in serum testosterone, by applying eGFR-related SNPs to testosterone in the UK Biobank. Results Genetically predicted testosterone was associated with CKD in men (odds ratio (OR) for bioavailable testosterone 1.17 per standard deviation, 95% confidence interval (CI) 1.03 to 1.33) based on 125 SNPs but not in women (OR 1.02, 95% CI 0.92 to 1.14 for total testosterone) based on 254 SNPs. Multivariable MR allowing for SHBG showed consistent patterns. Genetically predicted bioavailable testosterone in men and women and genetically predicted total testosterone in women increased hemoglobin and lowered HDL-c, as seen in RCTs. Genetically predicted eGFR was not related to serum testosterone in men or in women. Conclusions Genetically predicted testosterone was associated with CKD and worse kidney function in men, whilst not affected by kidney function. Identifying drivers of testosterone and the underlying pathways could provide new insights into CKD prevention and treatment.