Nucleotide mutations of the RNA polymerase 3 subunit b (polr3b) gene are responsible for hypomyelinating leukodystrophy 8 (HLD8), which is an autosomal recessive oligodendroglial cell disease. The gene discussed is POLR3B; the disease is hypomyelinating leukodystrophy 8 with or without oligodontia and-or hypogonadotropic hypogonadism.