HLA-DRB1 and primary biliary cholangitis: However, after excluding Bittencourt’s study [39], the difference in the number of individuals who carried the HLA-DRB1*13 allele, comparing PBC patients and controls, achieved significance (OR = 0.553, 95%CI: 0.419–0.729), and this occurred with a lower heterogeneity (I2 = 13.8%, P = 0.323), supporting the hypothesis that inclusion of this particular study may lead to bias.