Alpha Globin Gene Copy Number Is Associated with Prevalent Chronic Kidney Disease and Incident End-Stage Kidney Disease among Black Americans.

Abstract

<i>α</i>-Globin is expressed in endothelial cells of resistance arteries, where it limits endothelial nitric oxide signaling and enhances <i>α</i>-adrenergic-mediated vasoconstriction. <i>α</i>-Globin gene (<i>HBA)</i> copy number is variable in people of African descent and other populations worldwide. Given the protective effect of nitric oxide in the kidney, we hypothesized that <i>HBA</i> copy number would be associated with kidney disease risk. Community-dwelling Black Americans aged ≥45 years old were enrolled in a national longitudinal cohort from 2003 through 2007. <i>HBA</i> copy number was measured using droplet digital PCR. The prevalence ratio (PR) of CKD and the relative risk (RR) of incident reduced eGFR were calculated using modified Poisson multivariable regression. The hazard ratio (HR) of incident ESKD was calculated using Cox proportional hazards multivariable regression. Among 9908 participants, <i>HBA</i> copy number varied from 2 to 6. In analyses adjusted for demographic, clinical, and genetic risk factors, a one-copy increase in <i>HBA</i> was associated with 14% greater prevalence of CKD (PR, 1.14; 95% CI, 1.07 to 1.21; <i>P</i><0.0001). While <i>HBA</i> copy number was not associated with incident reduced eGFR (RR, 1.06; 95% CI, 0.94 to 1.19; <i>P</i>=0.38), the hazard of incident ESKD was 32% higher for each additional copy of <i>HBA</i> (HR, 1.32; 95% CI, 1.09 to 1.61; <i>P</i>=0.005). Increasing <i>HBA</i> copy number was associated with a greater prevalence of CKD and incidence of ESKD in a national longitudinal cohort of Black Americans.