SLC20A2 and primary biliary cholangitis: Nevertheless, the small number of PFBC and sporadic PBC cases linked to the various SLC20A2 variant types and the high degree of variation in onset of symptoms and their severity, even within PFBC families (Hsu et al. 2013; Nicolas et al. 2013a; Westenberger and Klein 2014; Yamada et al. 2014; Lemos et al. 2015; Nicolas et al. 2015), make studies of variant–phenotype correlations difficult.