Genetic factors have an impact on PBC pathogenesis that is stronger than that in nearly any other autoimmune disease [85] [86] [87] . Accordingly, a concordance rate of about 60% was seen in monozygotic twins (as opposed to nearly 0% for dizygotic twins) [88, 89] . A significantly increased incidence of PBC is seen in relatives of PBC patients [89, 90] . The relative risk of a first-degree relative of a PBC patient is 50-to 100-fold higher than for the general population [91] , yielding a prevalence rate up to 5-6% [19, 90, 92] . Interestingly, among affected monozygotic twins, though the age of disease onset is similar, progression and disease severity vary, emphasizing the role of epigenetic and probably environmental factors [89] .