An autosomal dominant neurodevelopmental disorder characterized by global developmental delay apparent in infancy. Affected individuals have delayed walking with variable gait abnormalities, including ataxia and spasticity, impaired intellectual development with poor or absent speech and language, and progressive microcephaly. Dysmorphic facial features may also be observed. Most patients have early-onset seizures; some may develop a demyelinating peripheral neuropathy. The clinical features suggest involvement of both the central and peripheral nervous systems.