Hypomyelinating leukodystrophies characterized by a combination of 3 major disorders:
These encompass a spectrum of 5 disorders
1. 4H: Hypomyelination, Hypodontia, and Hypogonadotropic hypogonadism
2. ADDH: Ataxia with delayed dentition and hypomyelination
3. LO: Leukodystrophy with oligodontia
4. TACH: Tremor ataxia with central hypomyelination
5. HCAHC: Hypomyelination with cerebellar atrophy and callosal hypoplasia
They have all been related to mutations in POLR3A or POLR3B.
On imaging their is increased T2 signal of the white matter. Decreased T2 signal may be seen in the posterior periventricular white matter (90%), posterior limb of the internal capsules (40%), the hila of the cerebellar nuclei (70%), globi pallidi, and the anterolateral thalami. Cerebellar atrophy (90%) and a thin corpus callosum.