CYCS and Leber hereditary optic neuropathy: OPA1 encodes for an inner mitochondrial membrane protein that regulates a host of important functions, including the balance between mitochondrial fusion and fission, the stability of the mitochondrial respiratory chain complexes, and the controlled release of proapoptotic cytochrome c molecules sequestered within the mitochondrial cristae.4 DOA is therefore a mitochondrially determined optic neuropathy characterized by the preferential loss of retinal ganglion cells within the inner retina, similar to Leber hereditary optic neuropathy (LHON).