In 2007, a case of lethal encephalopathy, which included optic atrophy in the clinical features, has been reported as caused by a de novo heterozygous dominant-negative mutation in DRP1. Patient fibroblasts showed hyperfusion of both peroxisomes and mitochondria, with depletion of peroxisomes and a few mitochondria displaying increased size and localization in the perinuclear region [159]. The gene discussed is DNM1L; the disease is Leber hereditary optic neuropathy.