rs2297508 — SREBF1 SREBF1 G952G

SREBF1 G952G — The Lipogenic Transcription Factor Variant

SREBP-1c¹¹ Full name: Sterol Regulatory Element-Binding Protein 1c — a membrane-bound transcription factor that is cleaved and activated by insulin to drive expression of fatty acid synthesis and glycolytic genes in liver and adipose tissue is the master switch for insulin-stimulated lipogenesis. Its gene, SREBF1, encodes both the SREBP-1a and SREBP-1c isoforms from separate promoters, with SREBP-1c being the dominant metabolic regulator in liver and fat cells. The rs2297508 variant — a C-to-G change that creates a synonymous coding change (G952G) in exon 18c and a functional 3' UTR element alteration — has been consistently linked to type 2 diabetes risk across European and Asian populations.

The Mechanism

The variant sits in the 3' untranslated region of the dominant SREBF1 transcript, where it may influence mRNA stability, microRNA binding, or post-transcriptional regulation of SREBP-1c expression. Because SREBP-1c is a mediator of insulin action²² mediator of insulin action
SREBP-1c is directly activated by insulin via an Akt-LXR-α signalling cascade, driving transcription of lipogenic genes including fatty acid synthase (FASN) and acetyl-CoA carboxylase (ACC), a subtle loss-of-function variant at this locus would be expected to blunt insulin's anabolic signalling in adipose tissue — shifting the metabolic phenotype toward insulin resistance and impaired adipokine secretion. The Felder et al. study found that the G/G genotype displayed the lowest circulating adiponectin levels among non-diabetic subjects (P = 0.0017), implicating SREBP-1c in the regulation of adiponectin gene expression. Separately, Laaksonen et al. showed that lathosterol³³ Lathosterol-to-cholesterol ratio is a validated serum marker of endogenous hepatic cholesterol synthesis rate, a marker of cholesterol synthesis, was significantly higher in CC homozygotes — indicating the G allele actually reduces hepatic cholesterol synthesis flux while increasing diabetes risk through a different pathway (impaired insulin signalling in adipose tissue). The precise causal mechanism at this locus remains under investigation.

The Evidence

The largest and most rigorous study is Grarup et al. (2008)⁴⁴ Grarup et al. (2008)
Grarup N et al. Association of variants in the sterol regulatory element-binding factor 1 (SREBF1) gene with type 2 diabetes, glycemia, and insulin resistance: a study of 15,734 Danish subjects. Diabetes, 2008, which genotyped rs2297508 and linked variants in the Inter99 population cohort (n = 6,070), the ADDITION trial (n = 8,662), and a Danish T2DM case-control cohort (n = 2,980 cases, 4,522 glucose-tolerant controls). The G allele showed OR 1.17 (95% CI 1.05–1.30, P = 0.003) for T2DM, and meta-analysis across all published studies confirmed the signal at OR 1.08 per G allele (P = 0.001). G allele carriers also showed significantly higher plasma glucose at 30 and 120 minutes and higher insulin at 120 minutes during an oral glucose tolerance test (all P < 0.006), consistent with impaired early insulin secretion or insulin resistance.

In 1,970 Austrians, Felder et al. (2007)⁵⁵ Felder et al. (2007)
Felder TK et al. The SREBF-1 locus is associated with type 2 diabetes and plasma adiponectin levels in a middle-aged Austrian population. Int J Obes (Lond), 2007 found GG carriers had OR 1.45 for T2DM and the lowest adiponectin levels among non-diabetic subjects (P = 0.0017), proposing adiponectin downregulation as the mediating mechanism.

In a Chinese case-control study, Liu et al. (2008)⁶⁶ Liu et al. (2008)
Liu J-X et al. Association of sterol regulatory element-binding protein-1c gene polymorphism with type 2 diabetes mellitus, insulin resistance and blood lipid levels in Chinese population. Diabetes Res Clin Pract, 2008 found the rs2297508 genotype distribution differed significantly between T2DM patients and controls (P = 0.002), with the minor C allele carriers having elevated LDL-c — a consistent signal across populations despite allele frequency differences.

Bouchard-Mercier et al. (2014)⁷⁷ Bouchard-Mercier et al. (2014)
Bouchard-Mercier A et al. SREBF1 gene variations modulate insulin sensitivity in response to a fish oil supplementation. Lipids Health Dis, 2014 randomised 210 adults to 5 g/day fish oil (EPA + DHA) for 6 weeks and found that the QUICKI insulin sensitivity index response differed significantly by SREBF1 genotype (P = 0.01), demonstrating that this variant directly modulates the metabolic benefit of omega-3 supplementation.

Practical Implications

The G allele's risk effect is modest per copy (OR ~1.08–1.17 per allele), but GG homozygotes carry roughly 45% increased odds of T2DM compared to CC homozygotes in European cohorts. Because the G allele is actually the population-major allele in Europeans (~57%) and Africans (~58%), GG is the most common genotype in these populations (~32–39% using Hardy-Weinberg estimates from allele frequency alone), though the Austrian and Mexican studies observed ~12% GG frequency, suggesting population-specific LD patterns. The key modifiable factors are those that compensate for impaired SREBP-1c function: insulin sensitivity optimisation through reduced refined carbohydrate load (insulin over-stimulation is the primary SREBP-1c activator, so blunting post-meal insulin spikes reduces lipogenic burden), omega-3 fatty acid supplementation (fish oil directly suppresses SREBP-1c transcription via PUFA-LXR competition, and this suppression is modulated by rs2297508 genotype), and monitoring of fasting glycaemia and adiponectin as early markers of the insulin-resistance phenotype.

Interactions

rs2297508 is in moderate linkage disequilibrium with rs11868035 (r² = 0.6–0.8) and rs12953299 in the same SREBF1 gene region. The Harding et al. (2006) Diabetologia study found rs11868035 tagged the primary association signal in UK populations. Combined carriage of multiple SREBF1 variants may produce a stronger phenotype than rs2297508 alone. SREBP-1c activity is also regulated upstream by insulin (via Akt), AMPK, and LXR-α, meaning variants in pathway genes (e.g., INSR, IRS1, PPARGC1A) may compound the functional deficit. Dietary omega-3 PUFAs suppress SREBP-1c mRNA directly through LXR competition, and the Bouchard-Mercier study demonstrates that the rs2297508 genotype modifies this nutrient-gene interaction.