While LHON is caused by three well-known pathogenic mtDNA mutations in the MT-ND1, MT-ND4, and MT-ND6 genes, DOA is caused by pathogenic mutations within the nuclear OPA1 gene, which codes for a mitochondrial wall membrane protein (Yu-Wai-Man et al., 2009; Wallace, 2010; Yu-Wai-Man et al., 2011). The gene discussed is MT-ND4; the disease is Leber hereditary optic neuropathy.