rs5925 — LDLR LDLR Expression Co-variant

LDLR's Hidden Splice Switch — When Silent Mutations Aren't Silent

The low-density lipoprotein receptor (LDLR) pulls cholesterol-carrying LDL particles out of the bloodstream and into liver cells for clearance. Most people know that rare LDLR mutations cause familial hypercholesterolemia, a severe inherited condition of massively elevated cholesterol. But LDLR is also shaped by a network of common regulatory variants that subtly tune how much functional receptor your liver produces — variants that don't alter the protein sequence at all, yet still affect cholesterol levels measurably.

rs5925 is one such variant. Located in exon 13 of LDLR, it produces a synonymous change (c.1959T>C, p.Val653=): both alleles encode valine, so the protein sequence is identical regardless of which allele you carry. Yet [multiple population studies across Chilean, Egyptian, South Indian, and Chinese cohorts | Rojas 2019; Alsabbagh 2022; Jha 2019; Wang 2023] have associated the C allele with higher LDL cholesterol and cardiovascular risk. The molecular explanation involves mRNA splicing — a key step in gene regulation that occurs after transcription but before the protein is made.

The Mechanism

Synonymous variants can profoundly affect gene output by disrupting exonic splicing enhancers (ESEs)¹¹ exonic splicing enhancers (ESEs)
Short RNA sequences within exons that signal to the spliceosome to include the exon in the mature mRNA. If an ESE is disrupted, the spliceosome may skip the exon, producing a truncated or non-functional protein.

The Lee et al. 2014 minigene study²² Lee et al. 2014 minigene study
Lee JD et al. Mutual effect of rs688 and rs5925 in regulating low-density lipoprotein receptor splicing. DNA Cell Biol, 2014 demonstrated that rs5925 and the nearby synonymous variant rs688 (exon 12) jointly control LDLR exon splicing efficiency. Using minigene constructs in human cell lines and confirmed in leukocyte RNA from patients, they measured how efficiently exon 12 and exon 13 were retained in mature LDLR mRNA across all four possible haplotype combinations:

• rs688-C / rs5925-C: 79.6% splicing efficiency (highest)
• rs688-C / rs5925-T: 76.7%
• rs688-T / rs5925-C: 69.0%
• rs688-T / rs5925-T: 68.5% (lowest)

rs5925 accounts for approximately 5.4% of splicing efficiency difference when rs688 carries the C allele. Critically, rs688-T (itself associated with reduced exon 12 inclusion) and rs5925-C rarely co-occur in high-splicing haplotypes in the populations where C-allele LDL elevation is observed — the predominant clinical haplotype combines rs688-T with rs5925-C, creating the TC combination with 69% efficiency versus the protective CC combination at 79.6%. This haplotype context explains why the population-level C allele effect on LDL is adverse despite rs5925-C appearing more efficient when paired with rs688-C.

The Evidence

Clinical evidence from multiple independent cohorts consistently links the C allele with higher LDL cholesterol. In a study of 178 healthy subjects from northern Chile³³ study of 178 healthy subjects from northern Chile
Rojas C et al. JCLA, 2019, individuals carrying at least one T allele had significantly lower total cholesterol, triglycerides, and LDL-C than CC homozygotes (p<0.05). The distribution in this Latin American population (CC 19%, CT 53%, TT 28%) closely matches Hardy-Weinberg predictions for a C allele frequency of ~45-53%, consistent with global gnomAD data.

In a case-control study of 400 South Indians⁴⁴ case-control study of 400 South Indians
Jha CK et al. Med Sci, 2019 (200 coronary artery disease patients, 200 matched controls), the heterozygous genotype at rs5925 was significantly protective against CAD (OR=0.45, 95% CI 0.27-0.75, p=0.002), demonstrating that the T allele confers cardiovascular protection beyond lipid levels alone.

An Egyptian study of 100 lupus nephritis patients⁵⁵ Egyptian study of 100 lupus nephritis patients
Alsabbagh YA et al. Arch Rheumatol, 2022 found the C allele significantly more prevalent in patients than healthy controls (60% vs 45%, p=0.003), with CC genotype carriers showing higher atherogenic index and LDL/HDL ratios. TT and CT genotypes showed significantly lower TC, TG, and LDL-C than CC homozygotes.

A 2023 Chinese adolescent study⁶⁶ 2023 Chinese adolescent study
Wang J et al. Int J Mol Sci, 2023 involving 709 students confirmed that male C allele carriers had elevated total cholesterol and LDL-C compared to TT homozygotes in the control group.

Notably, one Chilean pharmacogenomics study⁷⁷ Chilean pharmacogenomics study
Lagos J et al. Int J Mol Sci, 2015 examining atorvastatin response in 139 hypercholesterolemic subjects found no significant association between rs5925 and statin-induced LDL reduction (p=0.576). This suggests the variant's effect on LDLR expression levels does not meaningfully alter the pharmacodynamic response to statins, which primarily works through a separate mechanism (inhibiting cholesterol synthesis and upregulating LDLR protein quantity rather than splicing efficiency).

Practical Actions

For CC homozygotes, the elevated LDL risk is modest in absolute terms — this is not a pathogenic variant, and the LDL difference between genotypes is in the range of a few mg/dL to perhaps 10-15 mg/dL in studies with the largest effects. The practical implication is attentiveness: more frequent LDL monitoring, prompt action when cholesterol trends upward, and consideration of dietary and pharmaceutical interventions earlier rather than later.

Dietary strategies with the strongest LDL-lowering evidence independent of genotype — soluble fiber, plant sterols, reduced saturated fat — are particularly relevant for CC carriers since their genetic baseline LDLR efficiency is lower. These interventions enhance cholesterol clearance through mechanisms that can partially compensate for reduced splicing efficiency.

Because statin response does not appear to track with rs5925 genotype, standard lipid management guidelines apply to CC homozygotes who require pharmacotherapy.

Interactions

rs5925 functions within a two-SNP regulatory module with rs688. The splicing efficiency of LDLR exon transcripts is jointly determined by both variants, with rs688 being the dominant partner (accounting for ~9.4% vs rs5925's ~5.4% of the variation in splicing efficiency). Together, the rs688-T / rs5925-C haplotype produces the lowest splicing output. Individuals carrying both risk alleles (rs688-T and rs5925-C) have the most reduced LDLR mRNA splicing efficiency and may face compounded LDL-raising effects.

This variant also operates in the context of the broader LDLR regulatory landscape. rs6511720 (intron 1) modulates LDLR transcription through a sterol response element — it affects how much mRNA is produced before splicing even occurs. A CC homozygote at rs5925 who also carries the rs6511720 GG genotype (common, lower-expression) would experience a compounded reduction in functional LDLR output: reduced transcription AND reduced splicing efficiency. Conversely, rs6511720-T carriers (enhanced transcription) may partially offset the splicing inefficiency of the rs5925-C allele by producing more total transcript.