The five overlapping clinical phenotypes (described as distinct entities before their molecular basis was known) include: Hypomyelination, hypodontia, hypogonadotropic hypogonadism (4H syndrome); Ataxia, delayed dentition, and hypomyelination (ADDH); Tremor-ataxia with central hypomyelination (TACH); Leukodystrophy with oligodontia (LO); and Hypomyelination with cerebellar atrophy and hypoplasia of the corpus callosum (HCAHC).