A subset of leukodystrophies, named RNA polymerase III (Pol III)-related leukodystrophy or 4H (hypomyelination, hypodontia, and hypogonadotropic hypogonadism) leukodystrophy (MIM 607694, 614381)3, was found to be caused by biallelic pathogenic variants in genes that encode specific subunits of the enzyme Pol III, namely, POLR3A, POLR3B, POLR3K, and POLR1C. The gene discussed is POLR3B; the disease is tooth agenesis.