Developmental and epileptic encephalopathy-39 with leukodystrophy (DEE39) is an autosomal recessive neurologic syndrome characterized clinically by global developmental delay apparent in early infancy, early-onset seizures, hypotonia with poor motor function, and hypomyelination on brain imaging. Other features include absent speech and inability to walk; spasticity and hyperreflexia has also been reported. Although there is significant hypomyelination on brain imaging, the disorder was not classified as a primary leukodystrophy. The myelination defect was thought to stem from primary neuronal dysfunction due to impaired mitochondrial transport activity (summary by Wibom et al., 2009 and Falk et al., 2014). However, serial brain imaging in a patient with DEE39 by Kavanaugh et al. (2019) suggested that the mechanism of disease is consistent with a leukoaxonopathy type of leukodystrophy. For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Bosch-Boonstra-Schaaf optic atrophy syndrome (BBSOAS) is an autosomal dominant disorder characterized by delayed development, moderately impaired intellectual development, and optic atrophy. Most patients also have evidence of cerebral visual impairment. Dysmorphic facial features are variable and nonspecific (summary by Bosch et al., 2014).

Vertebral hypersegmentation and orofacial anomalies (VHO) is characterized by supernumerary cervical, thoracic, and/or lumbar vertebrae, in association with supernumerary ribs. Most patients also exhibit orofacial clefting and ear anomalies (Cox et al., 2019).