rs5888 — SCARB1

Synonymous variant that reduces SR-BI receptor expression and impairs HDL cholesterol uptake by the liver, lowering HDL-C levels and modestly increasing cardiovascular risk

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SCARB1 — The HDL Receptor Gene

Your liver clears cholesterol from the bloodstream using a receptor called SR-BI, encoded by the SCARB1 gene. SR-BI is the primary docking site where HDL particles offload their cholesterol cargo for processing and excretion in bile — the final step of reverse cholesterol transport11 reverse cholesterol transport
the process by which cholesterol is shuttled from peripheral tissues back to the liver for elimination. When SR-BI expression is reduced, HDL particles circulate longer without fully unloading their cargo, which can impair the liver's ability to process cholesterol and may subtly raise cardiovascular risk.

The rs5888 variant is a synonymous change in exon 8 of SCARB1 — synonymous meaning the amino acid sequence of the protein is unchanged. Yet the variant still matters: not every nucleotide change that preserves an amino acid is functionally neutral.

The Mechanism

Despite producing the same alanine amino acid (Ala350Ala), rs5888 alters the RNA secondary structure of the SCARB1 transcript. The T allele (the A allele on the genomic plus strand) creates a different codon — GCC instead of GCT — that causes the ribosomal machinery to stall. A key in vitro study22 key in vitro study
Constantineau et al. A synonymous variant in scavenger receptor, class B, type I gene is associated with lower SR-BI protein expression and function. Atherosclerosis, 2010 showed that cells expressing the risk variant have significantly lower SR-BI protein levels (p<0.04) and markedly reduced capacity for HDL cholesterol ester uptake (p<0.00001). The transcript levels are identical between genotypes — the difference is purely translational, with more mRNA trapped in non-translating ribosomal pools.

SR-BI also transports dietary carotenoids — particularly lutein and zeaxanthin — to the retinal pigment epithelium, where they form the macular pigment that filters harmful blue light. Impaired SR-BI activity can reduce delivery of these protective pigments to the macula, which may explain the AMD association described below.

The Evidence

A meta-analysis of 12 studies totalling 12,147 subjects33 meta-analysis of 12 studies totalling 12,147 subjects
Ye et al. Meta-analysis of the association between SCARB1 polymorphism and fasting blood lipid levels. Oncotarget, 2017 found that T-allele carriers (in plus-strand notation: A-allele carriers) had significantly higher HDL-C and lower triglycerides specifically in non-Asian men (SMD 0.15 for HDL-C; p≤0.001). A separate meta-analysis of 7 studies44 meta-analysis of 7 studies
Ma et al. SCARB1 rs5888 gene polymorphisms in coronary heart disease: A systematic review and meta-analysis. Gene, 2018 (6,360 subjects) found the T allele associated with reduced coronary heart disease risk in males (OR 0.79; 95% CI 0.61–1.01).

The effects are sex-specific and age-dependent. A Lithuanian population study55 A Lithuanian population study
Stanislovaitiene et al. SCARB1 single nucleotide polymorphism (rs5888) is associated with serum lipid profile and myocardial infarction in an age- and gender-dependent manner. Lipids Health Dis, 2013 of 2,439 subjects found that TT homozygous older males (65–74 years) had dramatically reduced MI risk (OR 0.24, 95% CI 0.10–0.56, p=0.001) and higher HDL levels. In young females (25–44 years), TT was associated with lower LDL-C. A smaller Amish cohort66 smaller Amish cohort
Roberts et al. Variants in scavenger receptor class B type I gene are associated with HDL cholesterol levels in younger women. Hum Hered, 2007 similarly found rs5888 associated with higher HDL-C in women under 50 but not in older women.

A pharmacogenomics study77 pharmacogenomics study
Wu et al. Sex-Specific Influence of the SCARB1 Rs5888 SNP on the Serum Lipid Response to Atorvastatin in Patients with Acute Coronary Syndrome. Pharmgenomics Pers Med, 2020 found that female ACS patients carrying the T allele had a greater reduction in LDL-C and ApoB after atorvastatin treatment, suggesting genotype-specific statin responsiveness in women.

AMD and Carotenoid Transport

A case-control study88 case-control study
Zerbib et al. rs5888 variant of SCARB1 gene is a possible susceptibility factor for age-related macular degeneration. PLoS One, 2009 in French and North American cohorts found that heterozygotes (CT genotype, i.e. AG in plus-strand notation) had substantially elevated AMD risk (pooled OR 2.9, 95% CI 1.6–5.3) compared to CC homozygotes — specifically among subjects without CFH or ARMS2 risk variants. The proposed mechanism is impaired SR-BI-mediated delivery of lutein and zeaxanthin to the retinal pigment epithelium.

This AMD association has not been replicated in large GWAS studies, so it should be interpreted as an emerging finding rather than established science.

Practical Actions

For the AA genotype (TT on coding strand), which has the lowest estimated SR-BI expression, the most directly actionable steps are dietary: ensuring adequate intake of preformed lutein and zeaxanthin (since SR-BI mediates their retinal delivery) and monitoring HDL-C as a surrogate for reverse cholesterol transport efficiency. For women on statins, the rs5888 genotype may influence treatment response, warranting closer monitoring.

Interactions

The lipid effects of rs5888 interact with those of CETP (rs708272) and LIPC (rs1532085) — genes that also regulate HDL metabolism. Individuals carrying risk alleles at multiple HDL pathway loci may have compounded HDL impairment beyond what rs5888 predicts alone. APOE (rs429358) interacts through a different mechanism: APOE ε4 impairs LDL clearance, and combined APOE4 + reduced SR-BI function could produce both LDL elevation and HDL impairment, though formal interaction studies are limited.

Nutrient Interactions

lutein altered_metabolism
zeaxanthin altered_metabolism

Genotype Interpretations

What each possible genotype means for this variant.

GG Full SR-BI Expression Normal

Normal SR-BI receptor expression and HDL cholesterol uptake

You carry two copies of the protective G allele (C allele on the coding strand), associated with normal SR-BI receptor expression and efficient HDL cholesterol uptake by the liver. About 29% of people globally share this genotype. Your reverse cholesterol transport pathway is not impaired by this variant.

AG Reduced SR-BI Expression Intermediate

One copy of the SR-BI risk allele — mildly reduced receptor expression

The heterozygous state shows intermediate SR-BI expression between GG and AA homozygotes, consistent with a codominant effect. Meta-analyses of lipid outcomes typically group AG + AA (T-allele carriers) together, making it difficult to isolate the heterozygote effect precisely. Most of the protective HDL signal observed in T-allele carriers reflects the combined genotype group, which appears predominantly driven by homozygous TT (AA on plus strand) carriers in older males and premenopausal females.

The AMD association identified by Zerbib et al. (2009) specifically highlighted heterozygotes as the risk group; homozygous TT was too rare in the AMD cohort for separate analysis. The proposed mechanism involves reduced SR-BI-mediated transport of lutein and zeaxanthin to the retina.

AA Lowest SR-BI Expression Decreased

Two copies of the SR-BI risk allele — reduced receptor expression and lower HDL cholesterol

The mechanistic basis is translational: the rs5888 T allele (A on the plus strand) creates an alternative codon (GCC instead of GCT for alanine-350) that alters RNA secondary structure and impairs ribosomal elongation. Cells expressing the TT variant show significantly lower SR-BI protein levels despite identical transcript levels, and significantly reduced HDL cholesterol ester uptake in functional assays. This is a well-characterized translational effect from a synonymous variant — a reminder that "silent" mutations are not always functionally neutral.

The AMD connection operates through a parallel SR-BI function: the same receptor mediates delivery of dietary carotenoids (lutein, zeaxanthin) to the retinal pigment epithelium. Reduced SR-BI activity may therefore limit macular pigment density and increase AMD susceptibility, independent of the lipid effects.

For women on atorvastatin, the T allele has been associated with greater LDL-C and ApoB reductions after treatment (Wu et al. 2020), suggesting that SR-BI influences statin pharmacodynamics in a sex-specific manner.