Coding and Noncoding Variants in CFH Act Synergistically for Complement Activation in Immunoglobulin A Nephropathy

Background: In immunoglobulin A nephropathy (IgAN), complement activation occurs in both the systemic circulation and in situ (glomerular). A recent IgAN-genome-wide association study (GWAS) identified 1q32 as an IgAN susceptible locus that contained the complement regulatory protein coding gene complement factor H (CFH). Here, we explored the combined genetic effects of coding and noncoding variants in CFH, rs6677604 and rs800292 on complement activation in IgAN. Methods: In total, 1,194 IgAN patients and 900 healthy controls who were the same as the Beijing Discovery Cohort in our recent IgAN-GWAS were recruited. The genotyping information of rs800292 and rs6677604 were extracted from GWAS data, while the information regarding plasma C3 levels and mesangial C3 deposits were collected from medical records. Results: We found both rs800292-GG and rs6677604-GG were risk genotypes for complement activation in IgAN patients, as represented by lower plasma C3 levels in IgAN patients with rs800292-GG and a higher intensity of glomerular C3 deposits in those with rs6677604-GG, respectively. Additionally, IgAN patients with 2 risk genotypes (rs800292-GG and rs6677604-GG) showed a higher degree of complement activation compared to those with no risk genotypes (rs800292-AA/AG and rs6677604-AA/AG), as represented by both lower plasma C3 levels and a higher intensity of glomerular C3 deposits. Moreover, when compared to rs800292 or rs6677604 alone, the combined genetic effects of rs800292 and rs6677604 showed a stronger association with IgAN susceptibility. Conclusions: Our findings suggested that both coding and noncoding variants in CFH acted synergistically to regulate the degree of complement activation and thereby contributed to IgAN susceptibility.