Sex-specific Associations of Sex Hormone Binding Globulin with CKD and Kidney Function: A Univariable and Multivariable Mendelian Randomization Study in the UK Biobank

Jie V. Zhao; C. Mary Schooling

doi:10.1681/ASN.2020050659

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Visual Abstract

Significance Statement

CKD exhibits sexual disparity, with renal function declining faster in men, which differences in sex hormone levels partially explain. Sex hormone binding globulin (SHBG), which modulates sex hormones, may also affect kidney function and contribute to the disparity. Mendelian randomization, a novel study design that considers genetic variants randomly allocated at conception, was applied to minimize residual confounding. The investigation is the largest sex-specific, genome-wide association study of SHBG variation on the largest cohort study of Europeans, the United Kingdom Biobank. Genetically predicted higher SHBG level was associated with lower risk of CKD and better kidney function in men but not in women. Identifying factors affecting SHBG, and underlying pathways, could provide new insights for prevention and treatment strategies.

Abstract

Background Kidney function declines faster in men. Testosterone levels may mediate the sex disparity. Correspondingly, levels of sex hormone binding globulin (SHBG), which modulates sex hormones, might also be relevant to the lower kidney function in men. The sex-specific role of SHBG is unclear.

Methods A sex-specific, Mendelian randomization (MR) study provided unconfounded estimates of SHBG levels among the United Kingdom Biobank population. Univariable MR applied 357 single nucleotide polymorphisms (SNPs) in men and 359 SNPs in women. These published SNPs strongly (P<5×10⁻⁸) predict SHBG level. They were profiled in 179,916 white British men (6016 patients with CKD) and 212,079 white British women (5958 patients with CKD), to obtain the effect of SHBG on CKD, albuminuria, and eGFR. Multivariable MR controlling for testosterone was used to assess the effect of SHBG on CKD and kidney function independent of testosterone in men.

Results Genetically predicted higher SHBG was associated with a lower risk of CKD in men (odds ratio [OR], 0.78 per SD; 95% confidence interval [95% CI], 0.65 to 0.93) but had no benefit in women. The effect in men remained in multivariable MR, allowing for testosterone (OR, 0.61; 95% CI, 0.45 to 0.82).

Conclusions Genetically predicted higher SHBG was associated with a lower risk of CKD and better kidney function in men, but not in women, suggesting that SHBG may play a role in CKD specifically in men. Identifying drivers of SHBG and the underlying pathways could provide new insights into CKD prevention and treatment.

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