Hence, optic atrophy is a common feature of mitochondrial disorders, and two other nonsyndromic causes of optic atrophy, LHON and autosomal dominant optic atrophy Kjer type, are caused, respectively, by mutations in mitochondrial DNA and the nuclear gene OPA1 that encodes a mitochondrial protein. Here, OPA1 is linked to Leber hereditary optic neuropathy.