rs2274700 — CFH A473A

CFH A473A — The Complement Haplotype Tag SNP for Macular Degeneration Risk

Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss in people over 65, and dysregulation of the complement immune system is its best-understood molecular driver. rs2274700 is a synonymous variant in exon 10 of CFH (Complement Factor H) — it does not change the amino acid sequence at position 473 (still alanine). Its significance lies not in any direct protein effect but in what it tags: rs2274700 is in complete linkage disequilibrium¹¹ complete linkage disequilibrium
LD measures how often two variants are inherited together; r²=1 means these two variants are perfectly correlated across populations with rs1410996, a well-characterized AMD risk variant in intron 1 of CFH that appears consistently in the GWAS-defined complement-risk haplotype.

In European populations, the G allele of rs2274700 occurs at roughly 60% frequency — making it the common allele — and it is this common allele that confers AMD risk. The protective A allele, found in only about 40% of Europeans, is consistently associated with lower AMD risk across multiple ethnic groups and is associated with better response to complement-targeted and anti-VEGF treatments. The 2022 Huan et al. study²² 2022 Huan et al. study
Identifying Novel Genes and Variants in Immune and Coagulation Pathways Associated with Macular Degeneration. Ophthalmology Science. 2022 confirmed the A allele protective OR of 0.64 (P=4.5×10⁻⁴) and established the perfect LD with rs1410996, explaining why this synonymous coding variant consistently appears in AMD association studies despite having no direct protein effect.

The Mechanism

CFH is a critical brake on the alternative complement pathway³³ alternative complement pathway
The complement system is an arm of innate immunity that can destroy pathogens and damaged cells via protein cascades; the alternative pathway runs continuously at a low level and must be tightly regulated to prevent self-damage. It acts primarily at mucosal and epithelial surfaces — including Bruch's membrane and the retinal pigment epithelium (RPE) — where it suppresses complement-mediated attack on healthy host tissue. Age-related accumulation of oxidized lipids, cellular debris, and advanced glycation end-products in the sub-retinal space provides an increasing stimulus for complement activation. Without adequate CFH suppression, this drives chronic inflammation that damages photoreceptors and the RPE, ultimately resulting in drusen (yellow lipid-protein deposits under the retina), geographic atrophy (dry AMD), or choroidal neovascularization (wet AMD).

The G-allele haplotype tagged by rs2274700 is associated with reduced CFH expression or function at retinal surfaces relative to the A-allele haplotype. Because rs2274700 is a synonymous variant in perfect LD with the functional intronic variant rs1410996, it is likely that the causal mechanism operates through altered splicing efficiency, mRNA stability, or regulatory element binding within the CFH genomic region, rather than through any amino acid change. In East Asian populations where the Y402H variant (rs1061170) shows weak association, rs2274700 and rs1410996 remain significant, suggesting they tag distinct functional variation within CFH independent of Y402H.

The Evidence

The AMD-rs2274700 association is well-replicated across ethnicities. Francis et al. 2007⁴⁴ Francis et al. 2007
Haplotypes in the complement factor H (CFH) gene: associations with drusen and advanced age-related macular degeneration. PLoS One. 2007 identified rs2274700 as the most strongly associated CFH SNP in their haplotype analysis across three independent AMD populations, reaching p<10⁻⁹ in combination with Y402H and rs1061147 — covering both early drusen formation and advanced AMD.

The large-scale Lu et al. 2018 meta-analysis⁵⁵ Lu et al. 2018 meta-analysis
53 studies, 110,747 participants of complement gene polymorphisms and AMD found a pooled heterozygote-model OR of 0.53 (95% CI 0.40–0.70) for rs2274700, consistent with a protective A-allele effect across Caucasian and Asian populations. Babanejad et al. 2016⁶⁶ Babanejad et al. 2016
Iranian case-control study, 100 AMD patients vs 100 controls independently confirmed the G allele as the risk allele with a significant case-vs-control frequency difference (p<0.001).

A notable nuance is the age-dependent effect documented by Adams et al. 2012⁷⁷ Adams et al. 2012
Melbourne Collaborative Cohort Study, 2,294 cases and 2,294 controls ages 48–86. Human Molecular Genetics. 2012: in participants under 55, the risk genotype showed a paradoxical inverse (protective) association with early AMD; in those over 75, the association reversed to a significant risk signal. This age-modulation likely reflects the progressive breakdown of complement regulation as the sub-retinal environment accumulates oxidative stress with aging, at which point the G-allele haplotype's reduced CFH function becomes clinically relevant.

The clinical relevance extends to treatment: Cui et al. 2025⁸⁸ Cui et al. 2025
BMJ Open Ophthalmology; 104 neovascular AMD patients treated with combercept anti-VEGF found that the A allele of rs2274700 was associated with significantly better treatment response to the anti-VEGF agent combercept, suggesting that genetic profiling of CFH variants may help guide treatment selection in neovascular AMD.

Practical Implications

rs2274700 genotype information is most useful as part of a multi-variant CFH risk profile alongside the Y402H variant (rs1061170) and ARMS2 A69S (rs10490924). The G allele at rs2274700 acts in the same complement-dysregulation direction as the C allele at Y402H — both impair CFH's protective function at the retina. Carrying GG at rs2274700 without the Y402H risk allele still meaningfully elevates AMD risk, particularly in East Asian populations where Y402H is rare but rs2274700/rs1410996 remain strongly associated.

The age-dependency finding argues for beginning retinal monitoring earlier than population guidelines suggest for GG homozygotes, since complement dysregulation appears to become clinically relevant as other age-related retinal stressors accumulate. Supplementation with lutein, zeaxanthin, and omega-3 fatty acids has an evidence base for AMD prevention that is relevant across all CFH risk genotypes.

Interactions

rs2274700 is in complete LD with rs1410996 (r²=1), meaning they are interchangeable markers for the same underlying CFH haplotype risk. The Y402H variant (rs1061170) is partially correlated — both mark complement-risk haplotypes but measure partially independent variation, as evidenced by rs2274700's independent significance in East Asian populations where Y402H shows no association. Combined high-risk genotypes at rs2274700 (GG) and rs10490924/ARMS2 (TT) confer synergistically elevated AMD risk through complementary pathogenic pathways: complement dysregulation (CFH) and retinal oxidative stress (ARMS2).