Hypomyelination and congenital cataract (HCC) is usually characterized by bilateral congenital cataracts and normal psychomotor or only mildly delayed development in the first year of life, followed by slowly progressive neurologic impairment manifest as ataxia, spasticity (brisk tendon reflexes and bilateral extensor plantar responses), and mild-to-moderate cognitive impairment. Dysarthria and truncal hypotonia are observed. Cerebellar signs (truncal titubation and intention tremor) and peripheral neuropathy (muscle weakness and wasting of the legs) are present in the majority of affected individuals. Seizures can occur. Cataracts may be absent in some individuals.

SH3TC2-related hereditary motor and sensory neuropathy (SH3TC2-HMSN) is a demyelinating neuropathy characterized by severe spine deformities (scoliosis or kyphoscoliosis) and foot deformities (pes cavus, pes planus, or pes valgus) that typically present in the first decade of life or early adolescence. Other findings can include cranial nerve involvement (most commonly tongue involvement, facial weakness/paralysis, hearing impairment, dysarthria) and respiratory problems.

Hypomyelinating leukodystrophy-13 is an autosomal recessive neurodegenerative disorder characterized by infantile onset of delayed psychomotor development, axial hypotonia, and spasticity associated with delayed myelination and periventricular white matter abnormalities on brain imaging. More variable neurologic deficits, such as visual impairment, may also occur. Some patients may experience cardiac failure during acute illness (summary by Edvardson et al., 2016). For a general phenotypic description and a discussion of genetic heterogeneity of HLD, see 312080.