Quantile-specific heritability of monocyte chemoattractant protein-1, and relevance to rs1024611-disease interactions.

BACKGROUND: Monocyte chemoattractant protein-1 (MCP-1) concentrations are 34% to 47% heritable. Larger -2518 G/A (rs1024611) genotypes differences are reported for: 1) MCP-1 production in stimulated vs. basal cells; and 2) MCP-1 concentrations in diseased (sepsis, brain abscess, hepatitis B virus, Alzheimer's disease, Behcet's disease, and systemic lupus erythematosus) vs. healthy patients. Those results suggest that the -2518 G/A effect size may depend on whether the phenotype is high or low relative to its distribution (quantile-dependent expressivity). METHOD: To test whether quantile-dependent expressivity applies more broadly to genetic influences on MCP-1 concentrations, quantile-specific offspring-parent (β(OP)) and full-sib regression slopes (β(FS)) were estimated by applying quantile regression to the age- and sex-adjusted serum MCP-1 concentrations of Framingham Heart Study families. Quantile-specific heritabilities were calculated as h(2) = 2β(OP)/(1 + r(spouse)) and h(2)={(1 + 8r(spouse)β(FS))(0.5)-1}/(2r(spouse))). RESULTS: Heritability (h(2) ± SE) of MCP-1 concentrations increased from 0.15 ± 0.05 at the 10th percentile of the MCP-1 distribution, 0.23 ± 0.04 at the 25th, 0.32 ± 0.05 at the 50th, 0.43 ± 0.07 at the 75th, and 0.44 ± 0.07 at the 90th percentile, or an 0.0041 ± 0.0009 increase for each one-percent increment in the MCP-1 distribution (P(linear trend) = 2.4 × 10(-5)) when estimated from β(OP), and (P(linear trend) = 7.7 × 10(-9)) when estimated from β(FS). Compared to the 10th percentile, β(OP)-estimated h(2) was 3-fold greater at the 90th percentile (P(difference) = 0.0003), and 6.9-fold greater when estimated from β(FS) (P(difference) = 3.3 × 10(-6)). Re-analysis of in vivo comparison of MCP-1 concentrations in controls vs. patients with MCP-1-elevating conditions, and in vitro studies of MCP-1 production in basal vs. stimulated cells, show rs1024611 genotypes differences that were consistent with quantile-dependent expressivity. CONCLUSION: The heritability of circulating MCP-1 concentrations is quantile-dependent.