POLR1C and leukodystrophy: A subset of leukodystrophies named RNA polymerase III-related leukodystrophy or 4 H (Hypomyelination, Hypodontia and Hypogonadotropic Hypogonadism) leukodystrophy [24] (MIM 607,694, 614,381) was found to be caused by biallelic pathogenic variants in genes encoding specific subunits of the enzyme Pol III, such as POLR3A [25–27], POLR3B [28], POLR3K [29] and POLR1C [30].