rs6908425 — CDKAL1

CDKAL1 — When the Translation Machine Misfires in Immune Cells

Inside every cell, a set of enzymes quietly edits transfer RNA — the molecular adaptors that read genetic code and build proteins. CDKAL1 encodes one of these editors: a methylthiotransferase¹¹ methylthiotransferase
An enzyme that adds a methylthio (-SCH₃) chemical group to a specific adenosine residue (ms²t⁶A₃₇) in tRNA, essential for accurate translation of codons beginning with adenosine that modifies tRNA at position 37, adjacent to the anticodon loop. This modification ensures the ribosome reads ANN codons faithfully — without it, mistranslation errors accumulate, affecting proteins whose synthesis depends on those codons. rs6908425 is an intronic variant in CDKAL1 whose C allele has been reproducibly associated with Crohn's disease risk across multiple large GWAS studies.

The Mechanism

rs6908425 sits in an intron of CDKAL1 at chromosome 6, position 20,728,500 (GRCh38). As an intronic variant it does not change the protein sequence directly, but it likely acts as a regulatory tag²² regulatory tag
Intronic variants can alter splicing efficiency, branch point usage, or intronic regulatory elements that control transcription. rs6908425 is in strong linkage disequilibrium with functional variants in CDKAL1 that affect gene expression levels.

Quaranta et al. (2009)³³ Quaranta et al. (2009)
Quaranta M et al. Differential contribution of CDKAL1 variants to psoriasis, Crohn's disease and type II diabetes. Genes & Immunity, 2009 made a critical observation: CDKAL1 transcripts are virtually absent from skin keratinocytes but are abundantly expressed in immune cells — particularly CD4+ T lymphocytes and CD19+ B lymphocytes — and are markedly downregulated when those cells receive proliferating signals. This expression pattern explains why CDKAL1 variants influence immune-mediated diseases: the gene's tRNA modification activity is most important in actively translating immune cells. Impaired tRNA editing in lymphocytes may reduce the fidelity of cytokine and receptor protein synthesis, contributing to dysregulated immune activation.

The Evidence

Barrett et al. (2008)⁴⁴ Barrett et al. (2008)
Barrett JC et al. Genome-wide association defines more than 30 distinct susceptibility loci for Crohn's disease. Nature Genetics, 2008 identified rs6908425-C as a Crohn's disease susceptibility allele with OR 1.21 (P=9×10⁻¹⁰) in a large multi-stage GWAS. This was replicated by Liu et al. (2015)⁵⁵ Liu et al. (2015) in a larger IBD meta-analysis (OR 1.11, P=5×10⁻¹²), and by Franke et al. (2010)⁶⁶ Franke et al. (2010) (OR 1.17, P=1×10⁻⁸). The same GWAS data showed a weaker ulcerative colitis association (OR 1.07, P=4×10⁻⁶), indicating the primary signal is in Crohn's disease specifically.

Quaranta et al. (2009)⁷⁷ Quaranta et al. (2009)
Quaranta M et al. Differential contribution of CDKAL1 variants to psoriasis, Crohn's disease and type II diabetes. Genes & Immunity, 2009 demonstrated that CDKAL1's risk allele for Crohn's disease and psoriasis is independent of the CDKAL1 T2D association: the same genomic region harbors distinct alleles driving disease-specific risk through different cell types. For psoriasis, the rs6908425 association reached OR 1.26–1.28 (combined P=4×10⁻⁶ across 2,579 cases and 4,306 controls).

Umeno et al. (2011)⁸⁸ Umeno et al. (2011)
Umeno J et al. Meta-analysis of published studies identified eight additional common susceptibility loci for Crohn's disease and ulcerative colitis. Inflammatory Bowel Disease, 2011 confirmed CDKAL1 among eight loci with modest effect sizes (OR 1.05–1.22) shared across IBD phenotypes. Evidence is strong: consistent replication across independent European and international cohorts with cumulative sample sizes in the tens of thousands.

The variant also shows a modest negative association with body mass index (beta −0.0095 per C allele, P=2×10⁻⁹) in a 2022 GWAS, consistent with CDKAL1's broader metabolic role in pancreatic beta cells and tRNA-mediated translational fidelity.

Practical Actions

Carrying one or two copies of the C allele does not guarantee Crohn's disease — it modestly shifts population-level risk. The C allele is common (~79% globally), meaning most people carry it. The actionable value for CC homozygotes lies in earlier vigilance for gastrointestinal symptoms, understanding of specific dietary patterns that support the intestinal mucosal barrier in genetically susceptible individuals, and awareness that anti-TNF biologic therapy is particularly relevant to this genetic risk pathway.

Crohn's disease in CDKAL1 C-allele carriers arises from a dysregulated mucosal immune response — supporting gut barrier integrity through targeted dietary and supplement strategies is genotype-relevant advice for CC individuals with gastrointestinal symptoms.

Interactions

CDKAL1 rs6908425 is part of a broader inflammatory genome. Its Crohn's disease signal is independent from the CDKAL1 T2D risk variants, demonstrating allelic heterogeneity at this locus. Individuals carrying both CDKAL1 risk alleles and IL23R risk alleles (rs11209026, rs2201841) have compounding risk for inflammatory bowel disease through the IL-23/Th17 pathway that governs mucosal immune responses in the gut. IBD risk is highly polygenic, and CDKAL1 C-allele status should be interpreted alongside ATG16L1, NOD2, and IL23R genotypes when available.