rs551397 — CFH

CFH's Haplotype Architecture — How rs551397 Tags Complement-Mediated AMD Risk

The complement factor H gene (CFH) spans nearly 100 kilobases on chromosome 1q31.3 and encodes the central brake on the alternative complement pathway. When Factor H is working normally, it binds C3b¹¹ C3b
the activated form of complement component C3 and prevents it from triggering an amplifying cascade that damages host tissue. When CFH variants shift this balance, the eye's Bruch's membrane²² Bruch's membrane
the thin extracellular matrix between the retinal pigment epithelium and the choroidal blood supply becomes a target for low-grade, chronic complement attack — the cellular substrate of age-related macular degeneration (AMD).

rs551397 is an intronic variant located in the CFH gene at chromosome 1 position 196,672,942 (GRCh38). It does not alter any amino acid, but it marks a haplotype block that has been associated with AMD across multiple Asian and European populations. The C allele tracks the risk haplotype; the T allele tracks the protective haplotype.

The Mechanism

CFH contains 20 short consensus repeat (SCR) domains that mediate its binding to C3b, heparin, and C-reactive protein — molecules concentrated at sites of tissue damage. rs551397 is in intron 1 (c.59-36 position in transcript NM_000186.4) and has no known direct functional effect on protein sequence or splicing. Its disease association arises primarily through linkage disequilibrium³³ linkage disequilibrium
the tendency for certain allele combinations to be inherited together because they rarely get separated by recombination with functionally important nearby variants, particularly the rs1061170 Y402H missense variant (the best-characterized AMD variant in CFH) and rs800292 (CFH Val62Ile).

A 2022 large-scale proteogenomics study (Gudjonsson et al.⁴⁴ Gudjonsson et al.
Large-scale proteogenomics reveals associations of genetic variants and serum proteins across the human body. Nature Genetics, 2022) found that rs551397 T allele carriers had measurably higher serum levels of complement factor B (CFB) — a key component of the alternative pathway C3 convertase — with an effect size of +0.29 standard deviations per T allele (p=9×10⁻⁴¹). This suggests the rs551397 haplotype block may influence complement pathway flux beyond the rs1061170 Y402H coding variant alone.

The Evidence

The AMD association for rs551397 has been replicated across multiple populations. In a Chinese case-control study of 163 AMD patients and 155 controls, Ng et al. 2008⁵⁵ Ng et al. 2008
Multiple gene polymorphisms in the complement factor H gene are associated with exudative age-related macular degeneration in Chinese. Invest Ophthalmol Vis Sci, 2008 found the TG haplotype across rs551397–rs800292 conferred an OR of 1.91 (95% CI 1.36–2.68, P=0.0001) for exudative AMD. A Korean study of 114 AMD patients and 240 controls (Kim et al. 2013⁶⁶ Kim et al. 2013
Ophthalmic Genetics, 2013) found individuals homozygous CC at rs551397 had OR=2.84, while C allele carriers had OR=1.67 for AMD.

The largest synthesis comes from a meta-analysis of 53 studies encompassing 53,774 AMD patients and 56,973 controls (Lu et al. 2018⁷⁷ Lu et al. 2018
Genet Test Mol Biomarkers, 2018), which found the rs551397 T allele was associated with reduced AMD risk at OR=0.53 (95% CI 0.45–0.61), with stronger protective effects in Caucasian populations than Asians. This substantial effect size — a 47% reduction in AMD odds per T allele — is clinically meaningful and positions rs551397 as a useful risk-stratification marker even when the well-studied Y402H variant is already known.

Population frequency varies dramatically: the protective T allele is rare in Europeans (~20%) but common in Africans (~71%), mirroring the lower AMD prevalence observed in African populations.

Practical Actions

For CC carriers — approximately 36% of the global population and ~65% of people of European ancestry — the elevated AMD risk from this haplotype is modifiable through targeted nutritional interventions. The AREDS2 trial⁸⁸ AREDS2 trial
Age-Related Eye Disease Study 2 demonstrated that supplementation with lutein/zeaxanthin and omega-3 fatty acids reduced progression from intermediate to advanced AMD. Complement-reducing dietary strategies — particularly reducing ultra-processed food intake and systemic inflammation — are the clearest mechanistic lever. Annual dilated eye exams beginning in the mid-40s provide the earliest window for intervention.

Interactions

rs551397 is in moderate linkage disequilibrium with rs1061170 (CFH Y402H), the most studied AMD variant globally, and with rs800292 (CFH Val62Ile). The Ng 2008 study defined the risk haplotype as T at rs551397 combined with G at rs800292 (in a Chinese population context where the risk architecture differs from European populations). In Europeans, the primary risk is carried by the C allele at rs551397 co-occurring with the C allele at rs1061170.

Individuals carrying risk alleles at both rs551397 and rs1061170 should discuss their compound complement risk with an ophthalmologist, as the combined effect likely exceeds either variant alone. The protective H7 haplotype (involving CFB rs641153 and C2 rs547154) may partially counteract CFH risk alleles, but this requires separate testing.