rs2043211 — CARD8 C10X

CARD8 C10X — Releasing the Inflammasome Brake

The NLRP3 inflammasome is a powerful intracellular alarm system that triggers fever, neutrophil recruitment, and systemic inflammation in response to infections and cellular damage. To prevent runaway activation, the cell maintains several internal brakes. CARD8 (caspase recruitment domain family member 8) is one of the most important: it binds directly to caspase-1¹¹ caspase-1
The effector protease of the NLRP3 inflammasome; when active it cleaves pro-IL-1β and pro-IL-18 into their mature, secreted forms and dampens its activity, preventing excessive IL-1β and IL-18 production. The C10X variant (rs2043211) introduces a stop codon at the tenth amino acid of CARD8, generating a truncated protein that cannot fulfil this inhibitory function. Roughly 1 in 10 people of European descent carries two copies of this truncating variant, and approximately 44% carry at least one copy.

The Mechanism

CARD8 normally acts through its CARD (caspase activation and recruitment domain)²² CARD (caspase activation and recruitment domain)
A protein interaction domain shared by many apoptosis and inflammation regulators; it mediates protein-protein binding through homotypic CARD-CARD interactions to physically bind and sequester caspase-1, reducing the amount of active enzyme available for IL-1β and IL-18 processing. The C10X nonsense variant (plus-strand T allele at chr19:48,234,449 GRCh38) places a stop codon at codon 10, well before the functional CARD domain. The truncated peptide is predicted to be rapidly degraded or non-functional, effectively deleting CARD8 activity in homozygous carriers. The result is an uninhibited caspase-1³³ uninhibited caspase-1
Without CARD8's brake, caspase-1 processes more pro-IL-1β and pro-IL-18 into their active secreted forms at any given level of NLRP3 activation that amplifies the inflammatory output of any NLRP3 stimulus. This is a loss-of-function variant: the T (truncating) allele removes a negative regulator, pushing inflammasome output upward.

The Evidence

The most clinically significant finding comes from a Swedish case-control study of 498 Crohn's disease patients: men who carried both the CARD8 C10X (this variant) and the NLRP3 Q705K gain-of-function variant (rs35829419) had OR 3.40 (95% CI 1.32-8.76, p=0.011) for Crohn's disease⁴⁴ men who carried both the CARD8 C10X (this variant) and the NLRP3 Q705K gain-of-function variant (rs35829419) had OR 3.40 (95% CI 1.32-8.76, p=0.011) for Crohn's disease
The sex-specific finding (no association in women) was replicated across two independent Swedish cohorts. Neither variant alone reached significance — the risk emerged from their combinatorial effect, consistent with the biology: Q705K is an overactive NLRP3 sensor, and C10X removes CARD8's capacity to brake it.

In rheumatoid arthritis, a Slovenian study of 128 patients treated with methotrexate found that TT genotype carriers had significantly higher DAS28 disease activity scores at diagnosis (p=0.022) and after 6 months of treatment (p=0.033)⁵⁵ TT genotype carriers had significantly higher DAS28 disease activity scores at diagnosis (p=0.022) and after 6 months of treatment (p=0.033)
DAS28 is a composite score of tender/swollen joint counts, ESR, and patient global assessment used to quantify RA disease burden, with the variant explaining approximately 8% of disease activity variability at diagnosis. In a Swedish RA cohort, carriers of at least one variant in both CARD8 and NLRP3 had adjusted OR 5.09 (95% CI 2.27-11.44, p<0.0001) for stroke and TIA⁶⁶ adjusted OR 5.09 (95% CI 2.27-11.44, p<0.0001) for stroke and TIA
The interaction was specific to cerebrovascular events, not myocardial infarction, suggesting an inflammasome-driven endothelial injury mechanism.

For psoriatic arthritis, a northern Swedish cohort study (724 PsA patients, 587 controls) found the AA genotype — homozygous for the normal, full-length CARD8 — was paradoxically associated with increased PsA susceptibility: OR 1.32 (95% CI 1.05-1.65, p=0.016)⁷⁷ increased PsA susceptibility: OR 1.32 (95% CI 1.05-1.65, p=0.016)
This finding illustrates that CARD8's inflammatory role in psoriatic disease differs from other arthritides; the exact mechanism is an active area of investigation. The opposite direction in PsA versus RA and Crohn's disease reflects that different autoimmune conditions depend on distinct immune pathways — in PsA, the relationship between innate inflammasome activity and adaptive T-cell-driven disease is more complex.

Protective effects of the truncating allele have also been observed in ankylosing spondylitis: a Swedish study (492 AS patients, 793 controls) found the C10X allele associated with decreased AS risk in a dominant model (OR 0.74, 95% CI 0.54-0.94, p=0.012)⁸⁸ decreased AS risk in a dominant model (OR 0.74, 95% CI 0.54-0.94, p=0.012)
AS is driven primarily by adaptive HLA-B27-mediated immunity; the modest protective effect of enhanced innate immune activity may reflect improved pathogen clearance reducing the microbial triggers that initiate AS.

Functional support comes from a 2024 study in 744 young healthy Swedes: the wild-type A allele was associated with higher CCL20 and IL-6 levels in men⁹⁹ the wild-type A allele was associated with higher CCL20 and IL-6 levels in men
This paradox (reference allele associated with higher inflammation) likely reflects unmeasured confounders in this cross-sectional cohort and does not contradict the mechanistic data, while the truncating T allele showed lower baseline cytokines in men — though interpretation is complicated by the sex-specific and cross-sectional nature of this finding.

Practical Actions

For carriers of one or two T alleles, the primary practical concern is monitoring for early signs of inflammatory conditions where CARD8-NLRP3 axis dysfunction is most clearly implicated: inflammatory bowel disease symptoms (particularly in men), RA disease activity if already diagnosed, and the combined risk with NLRP3 Q705K (rs35829419) if both variants are present. Nutritional strategies that suppress NLRP3 inflammasome activation — EPA/DHA omega-3 fatty acids (acting via GPR120/GPR40) and sulforaphane from broccoli sprouts — are the same interventions supported for NLRP3 gain-of-function variants and are particularly relevant when both CARD8 and NLRP3 variants are present.

Interactions

The critical interaction is with rs35829419 (NLRP3 Q705K). NLRP3 Q705K is a gain-of-function missense variant that lowers the inflammasome activation threshold, producing excess IL-1β at baseline. CARD8 C10X removes the endogenous brake on that overactive sensor. When both are present in men, Crohn's disease risk multiplies to OR 3.40 — a magnitude that neither variant achieves independently. This CARD8 C10X + NLRP3 Q705K combination also associates with stroke/TIA risk in RA patients (OR 5.09). Carriers of both variants warrant particularly close attention to dietary inflammasome management and IBD symptom surveillance.

rs2066844 (NOD2 R702W) and other NOD2 loss-of-function variants impair bacterial sensing in the gut. Combined NOD2 and CARD8/NLRP3 dysfunction may produce a double deficit in intestinal innate immunity — reduced bacterial detection plus dysregulated inflammasome-driven inflammation.