Leber hereditary optic neuropathy (LHON) is the most common mitochondrial disorder, with an estimated prevalence of 1 in 25,000.  Males are more likely to be affected than females.  Age of onset is between the ages of 18 to 30 years.  The first symptom is usually a sudden, painless, acute or subacute central vision loss; similar symptoms appear in the other eye at an average of two to three months later.  Visual loss generally occurs subacutely and then stabilizes.

Diagnosis of LHON relies on an ophthalmoscopic examination.  Testing includes dilated fundus examination to identify characteristic optic disc and vascular changes in the acute phase.  Swelling of the optic nerve head, vascular tortuosity, peripapillary telangiectasia, microangiopathy and central scotomas are all signs of LHON.  No effective therapy is available at this time, and management of this disorder is primarily supportive, with early introduction to visual aids and occupational therapy.  Gene therapy trials are currently underway.

LHON is caused by mutations in the mitochondrial DNA and it is transmitted by maternal inheritance.  Mutations in the NADH dehydrogenase, MT-ND1, MT-ND2, MT-ND4, MT-ND5, and MT-ND6, are known to be associated with LHON.  The most mutations found in about 95% of LHON patients are located in MT-ND1 (G3460A), MT-ND4 (G11778A), or MT-ND6 (T14484C) genes.  These three genes encode subunits of the respiratory chain complex I.  All mutations induce a decrease in ATP synthesis while increasing oxidative stress.  The T14484C mutation is associated with the best overall prognosis, with some visual recovery in 37-58% of cases.