POLR3B and leukodystrophy: Clinical manifestations and hypomyelination in 4H leukodystrophy are more severe in patients with variants in POLR3A and POLR1C than in patients with variants in POLR3B [7, 8]; hypomyelination, however, is not obligatory, and manifestation without hypomyelination occurs in patients with variants in POLR3A or POLR3B [9].