rs1831281 — CFH

CFH rs1831281 — A Complement Haplotype Marker Linking Inflammation and AMD Risk

The complement factor H gene (CFH) on chromosome 1q31.3 is one of the most well-studied genetic determinants of age-related macular degeneration (AMD) — the leading cause of irreversible blindness in adults over 65. rs1831281 is an intronic variant at position 196,711,684 (GRCh38) in intron 10 of CFH, annotated at transcript position c.1337-2051. Like several other CFH intronic variants (rs551397, rs1329428, rs1410996), it serves as a haplotype tag SNP¹¹ haplotype tag SNP
a genetic marker that travels with a cluster of risk variants across generations because of their proximity on the chromosome, marking the complement-risk haplotype architecture of the CFH gene.

The C allele is both the GRCh38 reference allele and the major allele, found in ~80% of Europeans. Despite being common, it tags the complement-risk haplotype — a well-documented pattern in the CFH region where the ancestral, common haplotype carries the AMD-risk configuration. The T allele (~20% in Europeans, ~10% in Africans, ~39% in East Asians) marks the protective haplotype and is associated with better complement regulation at the retina and other tissues.

The Mechanism

Complement Factor H²² Complement Factor H
a 155 kDa plasma glycoprotein that is the primary fluid-phase regulator of the alternative complement pathway works by binding C3b (the activated form of complement component 3) and accelerating the decay of the amplification convertase C3bBb. At mucosal surfaces — including the retinal pigment epithelium (RPE) and Bruch's membrane — CFH suppresses chronic, low-grade complement activation that would otherwise damage host tissue. Age-related accumulation of oxidized lipids, advanced glycation end-products, and cellular debris provides a progressive stimulus for complement activation in the sub-retinal space.

rs1831281 itself does not alter any amino acid. Its disease significance comes from linkage disequilibrium with functionally important variants in the surrounding CFH haplotype block — principally the well-characterized complement-risk alleles at rs551397 (intron 1), rs1329428 (intron 14), and the coding missense variant Y402H (rs1061170, exon 9). The C allele at rs1831281 travels on the same chromosome as the risk alleles at these adjacent positions; by carrying the C allele, a person is statistically more likely to also carry the full complement-risk haplotype configuration, which cumulatively reduces CFH's protective function at retinal and other complement-exposed surfaces.

A correction notice was issued for the Hughes et al. 2006 Nature Genetics study³³ Hughes et al. 2006 Nature Genetics study
A common CFH haplotype, with deletion of CFHR1 and CFHR3, is associated with lower risk of age-related macular degeneration. Nature Genetics 2006 regarding the allele designations of rs1831281 in Figure 1, confirming that this SNP was genotyped and used in CFH haplotype block analyses of AMD risk.

The Evidence

The AMD association of the CFH locus is one of the most replicated findings in complex disease genetics. Klein et al. 2005⁴⁴ Klein et al. 2005
Science — genome-wide screen of 116,000+ SNPs in 96 cases and 50 controls identified the CFH intronic region as the primary AMD susceptibility locus, with homozygous risk carriers showing a 7.4-fold increased likelihood of AMD. The CFH haplotype block where rs1831281 resides (intron 10, c.1337-2051) is part of this broader risk architecture.

Hageman et al. 2005⁵⁵ Hageman et al. 2005
PNAS — 900 AMD cases and controls further characterized the CFH risk haplotype, finding it in 50% of AMD cases versus 29% of controls (OR 2.46), with homozygous risk carriers comprising 24% of cases but only 8% of controls. Critically, risk and protective haplotypes were identified across the entire CFH gene including its intronic regions — the same structure encompassing rs1831281.

The large Lu et al. 2018 meta-analysis⁶⁶ Lu et al. 2018 meta-analysis
53 studies, 53,774 AMD patients, 56,973 controls. Genet Test Mol Biomarkers 2018 demonstrated that T-allele carrying CFH haplotype SNPs in this region are associated with OR=0.53 for AMD protection (95% CI 0.45–0.61), underscoring the magnitude of protection conferred by the complement-protective haplotype to which the T allele of rs1831281 belongs.

Regarding cardiovascular disease, the Sofat et al. 2010 meta-analysis⁷⁷ Sofat et al. 2010 meta-analysis
~48,000 participants, 9,097 CHD cases found that CFH genotype was not associated with coronary heart disease (pooled OR 1.02, 95% CI 0.91–1.13 for the Y402H risk allele). This meta-analysis result is expected to extend to other CFH haplotype-tag SNPs including rs1831281: the complement-inflammation pathway operates through AMD-specific retinal mechanisms rather than classical atherosclerotic pathways.

Practical Actions

The C allele at rs1831281 is clinically useful primarily as part of a multi-variant CFH risk profile. Its significance is amplified when co-occurring with risk alleles at rs1061170 (Y402H), rs551397, and rs800292 — and diminished when the protective T allele is present, which partially offsets the complement-risk haplotype background.

For CC homozygotes, the primary actionable implications are identical to those for other CFH complement-risk haplotype SNPs: earlier ophthalmologic surveillance, targeted macular carotenoid supplementation, and omega-3 optimization to reduce complement-driven retinal inflammation. Smoking cessation is particularly important as tobacco compounds CFH-pathway complement activation at the retina through oxidative and endothelial mechanisms.

Interactions

rs1831281 is in linkage disequilibrium with multiple CFH haplotype SNPs across the gene: rs551397 (intron 1), rs1329428 (intron 14), and the Y402H coding variant rs1061170. The AMD-risk C allele at rs1831281 is expected to co-occur with the risk alleles at these positions in most chromosomes carrying the risk haplotype, making it an additive signal rather than an independent risk factor. The most clinically meaningful two-locus interaction is with ARMS2 (rs10490924), where complement dysregulation (CFH) plus retinal oxidative stress (ARMS2) converge on two independent AMD pathogenesis pathways with synergistic risk elevation.