PLP1 disorders of central nervous system myelin formation include a range of phenotypes from Pelizaeus-Merzbacher disease (PMD) to spastic paraplegia 2 (SPG2). PMD typically manifests in infancy or early childhood with nystagmus, hypotonia, and cognitive impairment; the findings progress to severe spasticity and ataxia. Life span is shortened. SPG2 manifests as spastic paraparesis with or without CNS involvement and usually normal life span. Intrafamilial variation of phenotypes can be observed, but the signs are usually fairly consistent within families. Heterozygous females may manifest mild-to-moderate signs of the disease.

Laryngomalacia is a congenital abnormality of the laryngeal cartilage in which the cartilage is floppy and prolapses over the larynx during inspiration.

Neurodevelopmental disorder with central and peripheral motor dysfunction (NEDCPMD) is an autosomal recessive neurologic disorder with a highly variable phenotype. At the severe end of the spectrum, patients may have hypotonia apparent from birth, necessitating mechanical respiration and tube-feeding, and global developmental delay with absence of reaction to touch and no eye contact. At the mild end of the spectrum, patients may present with infantile-onset progressive ataxia and demyelinating peripheral neuropathy. The disorder is caused by mutation in the NFASC gene, which has several neuronal- and glial-specific transcripts. The variable clinical phenotype may be caused by several factors, including the severity of the mutation, the selective involvement of distinct isoforms by pathogenic variants, and the presence of genetic modifiers (summary by Monfrini et al., 2019).