rs838880 — SCARB1

SCARB1 — When the HDL Receptor Runs Quietly

SR-BI¹¹ SR-BI
Scavenger receptor class B type I; the primary hepatic receptor for selective cholesterol ester uptake from HDL particles sits at the end of the reverse cholesterol transport pathway — the arterial self-cleaning system that moves cholesterol from artery walls back to the liver. While most HDL-related genes work upstream, SR-BI is the final step: it docks HDL in the liver and extracts its cholesterol ester cargo, then sends the lipid-depleted particle back to scavenge more. When SR-BI runs less efficiently, that pipeline backs up — and the excess HDL sitting in circulation looks protective on a standard lipid panel but may not actually be doing its job.

The rs838880 variant sits in the 3' untranslated region (3'UTR) of SCARB1, a regulatory stretch of RNA that controls how much SR-BI protein is produced. It is one of the most replicated common variants at the SCARB1 locus and one of the original 95 lipid-influencing loci identified in the landmark 2010 Global Lipids GWAS²² 2010 Global Lipids GWAS
Teslovich et al. Biological, clinical and population relevance of 95 loci for blood lipids. Nature, 2010.

The Mechanism

The rs838880 T allele lies in a region of the SCARB1 3'UTR that may influence mRNA stability or translational efficiency — two key post- transcriptional mechanisms that determine how much SR-BI protein the liver actually produces from a given transcript. While the precise molecular mechanism has not been fully resolved for this specific variant, it tags a well-characterized haplotype associated with reduced hepatic SCARB1 expression ³³ Sex-specific regulation of SCARB1 expression in liver has been shown; gene variants interact with estrogen signalling to modulate SR-BI levels differently in men and women. Less SR-BI protein means slower selective uptake of cholesterol esters from HDL, resulting in marginally lower plasma HDL-C as measured in large population studies.

This is distinct from the dramatic paradox seen with rare loss-of-function missense mutations in SCARB1 (such as P297S), which cause pronounced hyperalphalipoproteinemia⁴⁴ pronounced hyperalphalipoproteinemia
Abnormally elevated HDL-C — the opposite of what most people consider a cardiovascular risk factor, yet associated with impaired cholesterol efflux and increased atherosclerosis in carriers of rare SR-BI mutations. At rs838880, the per-allele effect on plasma HDL-C is modest (~0.61 mg/dL per T allele), but the variant has been replicated at genome-wide significance in some of the largest lipid GWAS ever conducted.

The Evidence

The Global Lipids Genetics Consortium 2013 study⁵⁵ Global Lipids Genetics Consortium 2013 study
Willer et al. Discovery and refinement of loci associated with lipid levels. Nature Genetics, 2013 — the largest lipid GWAS at the time, with over 188,000 individuals — confirmed rs838880 as a significant HDL-C locus (C allele beta +0.048 SD units, p=6×10⁻³²). The T allele decreases HDL-C. The effect is additive and consistent across European, East Asian, and African ancestries.

A 2022 study of nephrosclerosis patients⁶⁶ 2022 study of nephrosclerosis patients
González et al. Tag-SNPs in Phospholipase-Related Genes Modify the Susceptibility to Nephrosclerosis and its Associated Cardiovascular Risk. Frontiers in Pharmacology, 2022 found that rs838880 was associated with nephrosclerosis susceptibility (OR 1.48, 95% CI 1.11–1.96, p=0.007) in 1,209 patients, suggesting the variant's cardiovascular-metabolic effects extend to renal vasculature.

The per-allele effect on HDL-C is modest. However, meta-analyses of SCARB1 rs5888⁷⁷ meta-analyses of SCARB1 rs5888
Ye et al. Meta-analysis of the association between SCARB1 polymorphism and fasting blood lipid levels. Oncotarget, 2017 — a coding variant in strong linkage disequilibrium with rs838880 — show that SCARB1 T-allele haplotypes are associated with higher HDL-C and lower triglycerides in non-Asian men but not women, consistent with sex-specific regulation of hepatic SR-BI expression.

Practical Actions

For TT homozygotes, the combined effect of two T alleles produces the lowest SR-BI-mediated HDL processing of the three genotypes. The actionable focus is on supporting the reverse cholesterol transport pathway through non-SR-BI mechanisms: increasing cholesterol efflux via ABCA1/ABCG1 (promoted by regular physical activity and soluble fiber), and monitoring lipid particle quality rather than just HDL-C quantity. Monitoring HDL particle number and function (via direct apolipoprotein A-I measurement) is more informative than HDL-C alone when SR-BI expression may be reduced.

Saturated fat intake is particularly relevant: high dietary saturated fat raises LDL-C and suppresses HDL-C in genetically predisposed individuals. Reducing saturated fat below 7% of total energy and substituting unsaturated fats is a specific strategy supported by the cardiovascular risk context of reduced SR-BI activity.

Interactions

rs838880 sits in a region of strong linkage disequilibrium with other SCARB1 variants including rs5888 (a synonymous coding variant with independent functional evidence) and rs10846744 (an intronic variant associated with CHD in Chinese populations). These variants may tag the same underlying haplotype. The rs11057830 SCARB1 intronic variant (already in the GeneOps database) affects a different functional outcome — carotenoid and vitamin E absorption — highlighting that SCARB1 has multiple independent functional regions.

Users carrying both reduced SR-BI expression (rs838880 TT) and APOE E4 (rs429358 CT/CC) would be expected to face compounded cardiovascular risk from both impaired reverse cholesterol transport and elevated LDL-C.