CTLA4 and STAT4 variants increase risk of autoimmune thyroid disease.

Autoimmune thyroid disease (AITD), which includes Graves' disease and Hashimoto's thyroiditis, results from a complex interplay between genetic susceptibility and environmental triggers. Research consistently identifies specific variants in the CTLA4 and STAT4 genes as significant contributors to this genetic risk.

Clinical and effectiveness evidence

Large-scale meta-analyses and case-control studies across diverse populations confirm that specific alleles of CTLA4 and STAT4 significantly increase the risk of developing AITD:

• CTLA4 rs231775 (+49A/G): The G allele is a well-documented risk factor. In Asian populations, studies have reported odds ratios (OR) for Graves' disease ranging from 1.34 to 3.81. While some European cohorts show more modest associations, the overall evidence across Han Chinese, Slovak, and Indian populations remains strong.
• CTLA4 rs3087243 (CT60): The G allele of this variant is also associated with increased susceptibility. In Han Chinese cohorts, the G allele carries an OR of approximately 1.58–1.63 for Graves' disease in both children and adults. Similar associations have been observed in Japanese and Croatian populations.
• STAT4 rs7574865: The T allele (specifically the TT genotype) is linked to a higher risk of AITD. Meta-analyses of multiple case-control studies indicate that individuals with the TT genotype have a 1.55 to 1.63 times higher risk of AITD compared to those with the GG or TG genotypes.

Mechanistic explanations

These genetic variants increase disease susceptibility by disrupting the fine-tuned regulation of the immune system:

• CTLA4 rs231775: Located in exon 1, this variant causes an amino acid substitution (alanine to threonine) in the leader peptide of the CTLA4 protein. This change reduces the expression and stability of CTLA4 on the surface of activated T-cells. Since CTLA4 is a critical "brake" for the immune system, its reduction allows autoreactive T-cells to attack thyroid antigens like thyroglobulin and thyroid peroxidase (TPO).
• CTLA4 rs3087243: Situated in the 3' untranslated region (UTR), the G allele affects the stability of CTLA4 mRNA. It promotes alternative splicing that favors the production of a soluble form (sCTLA4) over the functional membrane-bound form. This decrease in membrane-bound CTLA4 impairs the body's ability to downregulate T-cell activation, leading to a loss of self-tolerance.
• STAT4 rs7574865: This intronic variant modulates the JAK-STAT signaling pathway. The T allele is associated with the upregulation of STAT4 mRNA and protein expression. This increased expression makes T-cells hypersensitive to interleukin-12 (IL-12), driving them to become pro-inflammatory Th1 cells. These Th1 cells produce high levels of interferon-gamma (IFN-γ), creating an aggressive immune environment that targets the thyroid gland.

Bottom line

The CTLA4 (rs231775, rs3087243) and STAT4 (rs7574865) variants are confirmed genetic risk factors for autoimmune thyroid disease. They operate by impairing T-cell inhibitory checkpoints and enhancing pro-inflammatory signaling, though the magnitude of risk varies by ethnicity and specific disease subtype.