Fig. 3: Nonlinear Mendelian randomization analysis plots.
From: Mendelian randomization reveals causal effects of kidney function on various biochemical parameters
The fractional polynomial method of degree 2 was implemented to illustrate the shapes of causal estimates according to eGFR values. The eGFR values were calculated based on the creatinine–cystatin C CKD-EPI equation in the UK Biobank (available in 321,024 individuals). Age, sex, and 10 genetic principal components were included as adjusted covariates. The reference points (red dots) were set to eGFR 60 mL/min/1.73 m2, which is a conventional threshold to indicate reduced kidney function. The biochemical parameters for which the causal estimates were consistently significant in the summary-level MR were assessed by nonlinear MR analysis. The gray lines indicate the 95% confidence interval. The unit of eGFR was mL/min/1.73 m2, and the unit of measurements for biochemical parameters were as follows: hemoglobin concentration (grams/deciliter), lymphocyte percentage (percent), urine creatinine (micromole/L), alanine aminotransferase (U/L), urea (mmol/L), calcium (mmol/L), HDL cholesterol (mmol/L), insulin-like growth factor-1 (mmol/L), triglycerides (mmol/L), urate (µmol/L), and vitamin D (nmol/L).
