Pathogenic variants in DNM1L resulting in dysfunctional or absent DRP1 lead to a severe phenotype with neonatal lethality, epileptic encephalopathy, postnatal microcephaly, developmental delay and pain insensitivity118, 119 and to a milder phenotype with optic atrophy.120. The gene discussed is DNM1L; the disease is hereditary optic atrophy.