Neurodevelopmental disorder with severe motor impairment, absent language, cerebral hypomyelination, and brain atrophy (NEDMLHB) is characterized by the onset of these features soon after birth or in early infancy. Affected individuals make almost no developmental progress, are unable to sit or walk, do not acquire speech, have poor visual fixation, and show poor overall growth associated with feeding problems. Some may have a progressive disease course, suggesting neurodegeneration. Additional more variable features include seizures, spasticity, and joint contractures. Brain imaging shows hypomyelination, thin corpus callosum, and cerebral and cerebellar atrophy (Wong et al., 2022).

Neurodevelopmental disorder with hypotonia and speech delay, with or without seizures (NEDHSS) is characterized by global developmental delay, impaired intellectual development with poor or absent speech, and fine and gross motor delay. Most affected individuals are severely affected and may be unable to walk, have feeding difficulties requiring tube-feeding, and develop early-onset seizures. Additional features may include cortical blindness and nonspecific structural brain abnormalities. Rare individuals present only with hypotonia and mild developmental delay (Paul et al., 2023).

Neurodevelopmental disorder with hypotonia and characteristic brain abnormalities (NEDHBA) is an autosomal recessive disorder characterized by impaired intellectual development with striking radiologic abnormalities of the lateral ventricles (Fasham et al., 2023).