Can CTLA4 rs231775 GG and rs3087243 GG weaken immune checkpoint tolerance and be associated with autoimmune thyroid disease?

Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) is a critical checkpoint receptor that downregulates T-cell activation to maintain self-tolerance. Genetic variations in the CTLA4 gene can weaken this regulatory mechanism, predisposing individuals to autoimmune pathology.

Mechanistic pathways of checkpoint evasion

• Impaired membrane trafficking: The CTLA4 rs231775 GG genotype causes a Thr17Ala amino acid substitution in the signal peptide, which impairs protein glycosylation in the endoplasmic reticulum. This leads to retrograde transport and cytoplasmic degradation, significantly reducing membrane CTLA-4 expression on the T-cell surface.
• Reduced soluble decoy isoforms: The rs3087243 GG genotype, located in a 3′ untranslated cis-regulatory region, alters alternative splicing to significantly lower the production of soluble CTLA-4 (sCTLA-4) transcripts and protein.
• Loss of T-cell inhibition: Together, these twin defects compromise both membrane-bound and soluble CTLA-4, reducing the competitive blockade of costimulatory CD80/CD86 ligands on antigen-presenting cells. This lowers the threshold for T-cell activation and weakens overall immune checkpoint tolerance.

Clinical associations and autoantibody elevation

• Autoimmune thyroid disease susceptibility: Large-scale genetic analyses show that GG homozygous carriers of both variants exhibit a roughly two-fold higher relative odds of developing Graves' disease and have a established susceptibility to Hashimoto's thyroiditis.
• Elevated humoral autoimmunity: Carrying these risk alleles is directly associated with significantly higher titers of thyroid autoantibodies, including anti-thyroglobulin (TgAb) and anti-thyroid peroxidase (TPOAb). In active Graves' disease, these genotypes correlate with persistently elevated TSH receptor antibodies (TRAb) and higher rates of clinical relapse.

Bottom line

• The CTLA4 rs231775 GG and rs3087243 GG genotypes act via complementary pathways to reduce membrane and soluble CTLA-4 expression, causing impaired T-cell regulation that drives elevated thyroid autoantibodies and increases susceptibility to autoimmune thyroid diseases.