This may reflect shared genetic susceptibility and immune pathways, as susceptibility genes for AITD such as forkhead box protein P3 (FOXP3) and cytotoxic T-lymphocyte protein 4 (CTLA-4) can affect central and peripheral immune tolerance, thereby increasing the risk of developing other autoimmune diseases, including rheumatoid arthritis and systemic lupus erythematosus (155). Here, CTLA4 is linked to autoimmune disease.