Mutations that cause hypomyelinating leukodystrophy with 4H syndrome occur predominantly in the largest two subunits of Pol III, POLR3A and POLR3B (Rpc160 and Rpc128 in yeast, respectively) (Bernard et al., 2011; Saitsu et al., 2011; Shimojima et al., 2014; Synofzik et al., 2013; Terao et al., 2012; Tétreault et al., 2011), with a few in POLR1C (Rpc40 in yeast) (Thiffault et al., 2015), a subunit shared by Pol I and Pol III. This evidence concerns the gene POLR1C and leukodystrophy.