Are CTLA4 polymorphisms linked to reduced inhibitory T-cell signaling and higher risk of autoimmune thyroid disease?

Clinical evidence

• Strong association with Graves' disease: Large-scale case-control studies and genetic meta-analyses consistently link CTLA4 polymorphisms to autoimmune thyroid disease (AITD), showing the strongest, most reproducible associations with Graves' disease. The common coding variant rs231775 (+49A>G) and the 3'UTR variant rs3087243 (CT60) confer elevated risk across diverse ancestries, with odds ratios typically ranging between 1.3 and 1.7.
• Weaker association with Hashimoto's thyroiditis: The genetic risk link is less consistent for Hashimoto's thyroiditis. Several cohorts show weak or non-significant associations, indicating that while CTLA4 variants represent a major risk locus for Graves' disease, Hashimoto's thyroiditis may have a distinct or more heterogeneous genetic architecture.

Mechanistic explanations

• Altered receptor trafficking and splicing: The rs231775 (Thr17Ala) coding polymorphism disrupts the hydrophobic signal peptide of CTLA-4, which reduces its cell-surface expression and impairs its trafficking within T cells. Additionally, the rs3087243 variant alters the alternative splicing ratio, reducing full-length membrane-bound CTLA-4 while modulating circulating levels of the soluble CTLA-4 (sCTLA-4) isoform.
• Impaired T-cell regulation: Because CTLA-4 normally downregulates T-cell activation by competing with CD28 for CD80/CD86 ligands and removing them via trans-endocytosis, these hypomorphic variants compromise competitive inhibition. This results in lowered activation thresholds, unchecked CD28-mediated co-stimulation, and a functional loss of regulatory T-cell (Treg) suppressive capacity.

Bottom line

Polymorphisms in the CTLA4 gene (primarily rs231775 and rs3087243) are robustly associated with reduced inhibitory T-cell signaling and an increased risk of autoimmune thyroid disease, driven by functional alterations in receptor splicing, surface trafficking, and ligand competition that compromise immune tolerance.