Genetic Evidence for a Causal Role of Serum Phosphate in Coronary Artery Calcification: The Rotterdam Study

Abstract

Background Hyperphosphatemia has been associated with coronary artery calcification (CAC) mostly in chronic kidney disease, but the association between phosphate levels within the normal phosphate range and CAC is unclear. Our objectives were to evaluate associations between phosphate levels and CAC among men and women from the general population and assess causality through Mendelian randomization. Methods and Results CAC, measured by electron-beam computed tomography, and serum phosphate levels were assessed in 1889 individuals from the RS (Rotterdam Study). Phenotypic associations were tested through linear models adjusted for age, body mass index, blood pressure, smoking, prevalent cardiovascular disease and diabetes, 25-hydroxyvitamin D, total calcium, C-reactive protein, glucose, and total cholesterol : high-density lipoprotein cholesterol ratio. Mendelian randomization was implemented through an allele score including 8 phosphate-related single-nucleotide polymorphisms. In phenotypic analyses, serum phosphate (per 1 SD) was associated with CAC with evidence for sex interaction (P_interaction=0.003) (men β, 0.44 [95% CI, 0.30-0.59]; P=3×10^-9; n=878; women β, 0.24 [95% CI, 0.08-0.40]; P=0.003; n=1011). Exclusion of hyperphosphatemia, chronic kidney disease (estimated glomerular filtration rate <60 mL/min per 1.73 m²) and prevalent cardiovascular disease yielded similar results. In Mendelian randomization analyses, instrumented phosphate was associated with CAC (total population β, 0.93 [95% CI: 0.07-1.79]; P=0.034; n=1693), even after exclusion of hyperphosphatemia, chronic kidney disease and prevalent cardiovascular disease (total population β, 1.23 [95% CI, 0.17-2.28]; P=0.023; n=1224). Conclusions Serum phosphate was associated with CAC in the general population with stronger effects in men. Mendelian randomization findings support a causal relation, also for serum phosphate and CAC in subjects without hyperphosphatemia, chronic kidney disease, and cardiovascular disease. Further research into underlying mechanisms of this association and sex differences is needed.

Keywords: Mendelian randomization; chronic kidney disease; coronary artery calcification; hyperphosphatemia; phosphate.

Figure 1. Mendelian randomization results for serum phosphate and coronary artery calcification: allelic score method and leave‐1‐SNP‐out approach applied to the whole cohort.

Betas were derived from 2‐stage least square for the score as a single instrument and adjusted for age, sex, and 10 principal components. Results are expressed as change in outcome per 1‐SD increase in phosphate (0.16 mmol/L=0.49 mg/dL). Leave‐1‐SNP‐out approach: allelic score analyses with the subtraction of 1 SNP at‐a‐time. Closest annotated gene is displayed if known to be associated with (or possible related to) phosphate homeostasis.

Figure 2. Mendelian randomization results for serum phosphate and coronary artery calcification: allelic score method applied in subgroup analyses according to serum phosphate levels, kidney function, and prevalent cardiovascular disease.

Betas were derived from 2‐stage least square for the score as a single instrument and adjusted for age, sex, and 10 principal components. Results are expressed as change in outcome per 1‐SD increase in phosphate (0.16 mmol/L=0.49 mg/dL). CKD indicates chronic kidney disease, defined as a glomerular filtration rate <60 mL/min per 1.73 m². Prevalent CVD, prevalent cardiovascular disease, defined as prevalent myocardial infarction, revascularization, stroke, and heart failure; HyperP, hyperphosphatemia, defined as a phosphate level >1.45 mmol/L (=4.5 mg/dL).