CTLA-4 gene polymorphism confers susceptibility to primary biliary cirrhosis

Background/Aim: Primary biliary cirrhosis (PBC) is an autoimmune cholestati c liver disease thought to develop through a complex interaction of genetic and environmental factors. It is characterised by T-cell-mediated non-supp urative destructive cholangitis. We have studied the polymorphic cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) gene, which encodes a molecule t hat is a vital negative regulator of T-cell activation, as a candidate susc eptibility locus for PBC, This gene on chromosome 2q33 (designated IDDM12) is associated with susceptibility to both type 1 diabetes and autoimmune th yroid disease. Methods: The CTLA-4 exon 1 polymorphism (A/G encoding for threonine or alan ine, respectively) was genotyped via polymerase chain reaction in 200 Cauca soid PBC patients and 200 non-related geographically matched Caucasoid cont rols. Results: There was significant overrepresentation of the G/A and G/G genoty pes in PBC patients compared to controls (G/A 53% vs 40%; G/G: 18.5% vs 10. 5%, Odds Ratio (OR)=2.45 [95% CI 1.6-3.7], p= 0.00006, chi(2)=19.4). Likewi se, there was a significant difference in allele frequencies (G encoding al anine at codon 17, PBC 0.45 vs controls 0.305: OR=1.9 [1.4-2.5], p<0.0002). This association remained significant (p=0.00027) when patients with autoi mmune thyroid disease were excluded from the analysis. Conclusions: The CTLA-4 exon 1 polymorphism is the first non-major histocom patibility complex gene to be identified as a susceptibility locus for PBC, Our data support the hypothesis that clinically distinct autoimmune diseas e may be controlled by a common set of susceptibility genes.