MFN2 and Charcot-Marie-Tooth disease axonal type 2S: For example, mutations in the mitochondrial fission gene OPA1 cause autosomal dominant optic atrophy, while mutations in mitochondrial fusion genes, such as mitofusin-2 (MFN2), cause overlapping neurodegenerative phenotypes, including axonal peripheral neuropathy (Charcot-Marie-Tooth neuropathy type 2, CMT2)19,20.