rs725613 — CLEC16A

Intronic variant in the autophagy regulator CLEC16A, influencing risk for type 1 diabetes and multiple sclerosis

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CLEC16A — The Thymic Gatekeeper of Immune Tolerance

Your immune system must learn to attack pathogens without attacking your own tissues — a balancing act that starts in the thymus, where T cells are educated and self-reactive cells are eliminated. CLEC16A encodes an E3 ubiquitin ligase that controls autophagy11 autophagy
the cellular recycling process that breaks down damaged proteins and organelles in thymic epithelial cells. rs725613 is one of three intronic CLEC16A variants in strong linkage disequilibrium22 linkage disequilibrium
correlated alleles inherited together as a block, so they tag the same underlying signal that have been associated with both type 1 diabetes and multiple sclerosis.

The Mechanism

CLEC16A sits within a critical gene cluster on chromosome 16p13 alongside CIITA, DEXI, and SOCS1 — genes governing immune cell differentiation and cytokine signaling.

The biological consequence flows through autophagy. Thymic epithelial cells (TECs) use autophagy to process and present self-antigens to developing T cells during negative selection — the process that eliminates T cells capable of attacking the body. Reducing CLEC16A expression33 Reducing CLEC16A expression
Mouse models with reduced Clec16a in thymic epithelium produced T cells with lower autoreactivity and were protected against T1D impairs TEC autophagy, which alters the self-antigen repertoire presented to thymocytes. The result is subtly altered T-cell selection — the thymus graduates T cells with a slightly different reactivity profile.

The variant also influences CLEC16A expression in pancreatic β-cells44 pancreatic β-cells
the insulin-producing cells destroyed in type 1 diabetes, where CLEC16A maintains mitochondrial quality control through mitophagy. Impaired mitophagy in β-cells leads to mitochondrial dysfunction and compromised insulin secretion, potentially contributing to T1D pathogenesis through a second, peripheral mechanism independent of T-cell selection.

The Evidence

The rs725613 signal was discovered in a genome-wide association study of Northern European T1D patients and replicated across populations. A Sardinian cohort study55 Sardinian cohort study
Zoledziewska et al., Genes & Immunity, 2009 — rs725613 allele A associated with T1D (OR 1.15) and MS (OR 1.21) in 1,037 T1D cases, 1,498 MS cases, and 1,706 controls demonstrated that the same variant confers risk for both T1D and MS with comparable effect sizes — unusual evidence for a shared immunological pathway underlying two clinically distinct diseases.

Fine-mapping in a German MS cohort66 Fine-mapping in a German MS cohort
Nischwitz et al., Acta Neurologica Scandinavica, 2011 — 31 CLEC16A SNPs genotyped in 603 MS patients and 825 controls; four intron-19 SNPs associated, rs725613 replicated confirmed rs725613 as a genuine MS risk signal and localized the effect to an ~50 kb linkage disequilibrium block within intron 19. A meta-analysis77 meta-analysis
Tang et al., PLoS One, 2013 — 1,803 T1D cases and 3,271 controls; rs725613 G allele OR 0.71 (95% CI 0.55–0.92), p=0.01, classified as protective for T1D pooling 1,803 T1D cases confirmed the protective effect of the G allele (OR 0.71 for T1D).

The G allele frequency varies markedly by ancestry: ~37% in Europeans, ~19% in East Asians, and ~59% in Africans. This population stratification helps explain why CLEC16A associations were initially discovered in European cohorts — East Asians carry fewer copies of the protective G allele and thus have a higher background rate of the risk-associated T allele at this locus.

CLEC16A variants have also been associated with at least 16 additional autoimmune conditions including systemic lupus erythematosus, celiac disease, Crohn's disease, and rheumatoid arthritis88 systemic lupus erythematosus, celiac disease, Crohn's disease, and rheumatoid arthritis
Comprehensive review of CLEC16A function across autoimmune conditions including 18 GWAS-confirmed disease associations, underscoring the gene's broad role in immune tolerance across multiple tissues.

Practical Actions

The TT genotype (risk-allele homozygotes) carries modestly elevated odds for T1D (OR ~1.15–1.3 per allele dose) and MS (OR ~1.21 per allele dose). These are moderate effects in the context of multifactorial diseases — other genetic and environmental factors dominate absolute risk. The actionable insight is targeted monitoring: T1D and MS both have early biomarkers that enable earlier intervention when caught proactively.

For T1D, autoantibody screening (anti-GAD65, anti-IA-2, anti-ZnT8, anti-insulin) can detect pre-clinical immune activation years before β-cell destruction becomes symptomatic. For MS, familiarity with early neurological symptoms — visual changes, numbness, weakness, balance problems — enables prompt MRI and neurological evaluation. Vitamin D insufficiency is a documented modifiable risk factor for both conditions; genotype-guided vitamin D optimization is a specific, actionable step for CLEC16A risk carriers.

Interactions

rs725613 is in strong LD with rs2903692.

Genotype Interpretations

What each possible genotype means for this variant.

GG Protective Genotype Beneficial

Two copies of the protective G allele — reduced autoimmune disease risk

The GG genotype is the most protective state at this locus. The G allele (equivalent to the C allele in minus-strand notation used in earlier papers) corresponds to lower T1D and MS risk in replicated association studies. The meta-analysis OR for T1D protection is approximately 0.71 per G allele, meaning GG homozygotes have roughly 50% lower odds at this locus compared to TT homozygotes. This does not eliminate autoimmune risk — HLA haplotypes, PTPN22, and environmental triggers (vitamin D deficiency, viral exposures) dominate absolute risk far more than any single GWAS variant — but it represents a favorable CLEC16A contribution.

GT Intermediate Risk Intermediate

One copy of the risk T allele — mildly elevated autoimmune susceptibility

The heterozygous state produces an intermediate phenotype — less effective than GG but substantially less impactful than TT. In absolute terms, the incremental T1D risk from one T allele is small; background population risk for T1D in Europeans is approximately 0.3–0.5%, and an OR of 1.15 translates to roughly 0.35–0.6% risk, a modest difference. MS risk shows a similar modest increment.

TT Risk Homozygote High Risk

Two copies of the risk T allele — elevated autoimmune susceptibility at this locus

TT is a modest population risk factor — the vast majority of TT individuals never develop T1D or MS — but it justifies targeted proactive monitoring strategies.