POLR3K and leukodystrophy: POLR3-HLD is caused by biallelic pathogenic variants in genes encoding subunits of the transcription complex RNA polymerase III (POLR3), namely POLR3A, POLR3B, POLR1C, and POLR3K (Bernard et al., 2011; Tétreault et al., 2011; Daoud et al., 2013; Thiffault et al., 2015; Dorboz et al., 2018).