rs1800947 — CRP +1059G>C

The Paradox of Lower Inflammation, Higher Risk

C-reactive protein (CRP) is the body's most ancient and abundant inflammatory marker, a pentameric acute-phase protein synthesized by the liver in response to IL-6 signaling¹¹ synthesized by the liver in response to IL-6 signaling
CRP production increases 1000-fold during acute inflammation. While elevated CRP unambiguously predicts cardiovascular disease, the rs1800947 polymorphism presents a paradox: the variant that lowers your inflammatory marker may simultaneously increase your cancer risk. This SNP sits at position +1059 in exon 2 of the CRP gene on chromosome 1q23.2, creating a synonymous mutation (p.Leu184Leu) that changes the codon from CTG to CTC without altering the leucine amino acid at position 184.

The Mechanism

Despite being "silent" at the protein level, rs1800947 profoundly affects CRP expression through post-transcriptional mechanisms. Synonymous variants can alter mRNA stability, translation kinetics, and splicing efficiency²² Synonymous variants can alter mRNA stability, translation kinetics, and splicing efficiency
Codon optimality determines mRNA half-life independent of translation rate by changing codon usage patterns and local mRNA secondary structure. The CTG→CTC change at rs1800947 appears to enhance mRNA stability or translation efficiency, paradoxically increasing baseline CRP production from the reference G allele while the C allele produces less.

The direction of effect is clear and consistent: C-allele carriers show 24-38% lower plasma CRP levels³³ C-allele carriers show 24-38% lower plasma CRP levels
Study in Han Chinese population (PMID 22763479) compared to GG homozygotes. In unstable angina patients, C-allele carriers had CRP levels of 2.3 mg/L versus 5.9 mg/L in GG homozygotes⁴⁴ C-allele carriers had CRP levels of 2.3 mg/L versus 5.9 mg/L in GG homozygotes
105-patient cardiovascular cohort, representing a 61% reduction. This effect persists across diverse populations and clinical contexts, from healthy elderly Japanese⁵⁵ healthy elderly Japanese
Arterial stiffness study (PMID 16832152) to Turkish women with hypertension⁶⁶ Turkish women with hypertension
1,138-adult Turkish cohort, though effect sizes vary by ethnicity and sex.

The Evidence

The cardiovascular evidence initially appears protective. In 105 patients with unstable angina followed for 24 months, C-allele carriers experienced fewer coronary events than GG homozygotes⁷⁷ C-allele carriers experienced fewer coronary events than GG homozygotes
Lower CRP correlated with better outcomes, consistent with the hypothesis that genetically lower CRP reflects reduced inflammatory burden. After coronary artery bypass surgery, C-allele carriers showed lower peak postoperative CRP levels (P=2.4×10⁻⁴)⁸⁸ C-allele carriers showed lower peak postoperative CRP levels (P=2.4×10⁻⁴)
604 CABG patients study, suggesting faster resolution of surgical inflammation.

Yet the atherosclerosis data tells a more complex story. In healthy elderly Japanese, the C-allele associated with increased arterial pulse wave velocity (p=0.039)⁹⁹ the C-allele associated with increased arterial pulse wave velocity (p=0.039)
Arterial stiffness marker of atherosclerosis, a marker of arterial stiffness and subclinical atherosclerosis. This finding seems paradoxical given that C-allele carriers have lower CRP — until we consider that CRP is not merely a biomarker but an active participant in vascular inflammation and atherosclerotic plaque stability.

The cancer evidence is where the paradox becomes stark. A meta-analysis of 5,601 cancer cases and 8,669 controls across 12 studies¹⁰¹⁰ meta-analysis of 5,601 cancer cases and 8,669 controls across 12 studies
Systematic review examining CRP polymorphisms and cancer risk found that the CC genotype was associated with a 4.5-fold increased risk of colorectal cancer compared to GG (OR 4.527, 95% CI 1.664-12.315, p<0.01). This association was specific to colorectal cancer and specific to CC homozygotes — heterozygotes showed no elevated risk. The mechanism remains unclear, but chronic inflammation is a well-established driver of colorectal carcinogenesis, and CRP directly binds to damaged cells and activates complement¹¹¹¹ CRP directly binds to damaged cells and activates complement
CRP functions in innate immunity and damaged cell clearance, playing a role in clearing premalignant cells.

Practical Implications

Your rs1800947 genotype influences your baseline CRP production capacity, with implications for both cardiovascular and cancer risk that depend critically on which genotype you carry.

If you're a GG homozygote (92% of most populations), you produce more CRP constitutively. This translates to higher baseline inflammatory markers that independently predict cardiovascular events¹²¹² higher baseline inflammatory markers that independently predict cardiovascular events
Elevated hs-CRP predicts CVD mortality with RR 2.03, particularly when combined with obesity, metabolic syndrome, or smoking. The standard interventions apply with particular force: Mediterranean diet reduces CRP by ~1.0 mg/L¹³¹³ Mediterranean diet reduces CRP by ~1.0 mg/L
Meta-analysis of 33 RCTs, 3,476 participants, aerobic exercise lowers CRP by 0.34-0.59 mg/L¹⁴¹⁴ aerobic exercise lowers CRP by 0.34-0.59 mg/L
Systematic review of exercise interventions, and smoking cessation reduces CRP by 0.40 mg/L¹⁵¹⁵ smoking cessation reduces CRP by 0.40 mg/L
Study in cardiovascular disease patients. Weight loss produces approximately 0.13 mg/L reduction per kilogram lost.

If you're a GC heterozygote (8% of Europeans), your baseline CRP falls between the extremes. The cancer risk data show no elevation for heterozygotes, suggesting the protective cardiovascular effect of lower CRP comes without the homozygous CC cancer liability.

If you're a CC homozygote (1% of Europeans, higher in some East Asian populations), you face a complex risk profile. Your constitutively lower CRP may reduce cardiovascular inflammatory burden in the short term, but the 4.5-fold elevated colorectal cancer risk demands aggressive screening. The mechanism linking low CRP to colorectal cancer remains speculative — it may involve impaired immune surveillance of premalignant colonic epithelium, altered gut microbiome interactions, or disrupted clearance of damaged cells. Colorectal cancer screening guidelines recommend colonoscopy every 10 years starting at age 45¹⁶¹⁶ Colorectal cancer screening guidelines recommend colonoscopy every 10 years starting at age 45
USPSTF recommendations for average-risk adults, but CC homozygotes should discuss earlier and more frequent screening with their physician.

Interactions

The rs1800947 variant exists in linkage disequilibrium with other CRP gene polymorphisms, particularly rs1205 (3' UTR, +1846C>T), rs1130864, rs3093059, and rs2794521. These variants together form haplotypes that determine CRP expression across a wider range than any single SNP. The CGCA haplotype (including specific alleles at these positions) associates with decreased type 2 diabetes risk¹⁷¹⁷ The CGCA haplotype (including specific alleles at these positions) associates with decreased type 2 diabetes risk
Turkish population haplotype analysis, suggesting that the rs1800947-rs1205 combination modulates not just CRP levels but downstream metabolic consequences.

The rs1800947 C-allele appears to have opposite effects in healthy populations versus severe acute illness. While it lowers baseline CRP, preliminary evidence suggests it may impair the acute-phase response capacity during sepsis or severe infection, similar to what has been documented for rs1205 TT carriers during COVID-19. If you carry the CC genotype, low CRP during acute illness should not be falsely reassuring — you may mount a blunted inflammatory response despite serious infection.

Gene-environment interactions are particularly relevant. The C-allele's CRP-lowering effect is most pronounced in populations with higher baseline inflammation due to obesity, poor diet, or chronic stress. In metabolically healthy, lean individuals, the genotype effect is modest. This suggests that rs1800947 modulates the magnitude of CRP response to inflammatory stimuli rather than setting an absolute baseline.