A further interesting correlation between TNF-α and CTLA-4 noted that single nucleotide polymorphism (SNP) rs1800629 of the TNF-α gene, leading to increased TNF-α production, amplified the CTLA4 SNP risk associated with rs231725, and that the combination of both SNPs was significantly more common in PBC patients compared to healthy controls (84). Here, CTLA4 is linked to primary biliary cholangitis.