The patient had bilateral optic neuropathy. The most likely cause was Leber’s hereditary optic neuropathy (LHON). This is a genetic mitochondrial disease, and it is maternally inherited because people derive their mitochondria derive from their mother. There is bilateral but not always symmetrical visual loss that usually occurs in young adulthood. However, the onset of disease has been reported between the ages of 7-75. Curiously, 50% of males and 85% of females who carry one of the three mutations known to cause this condition never manifest optic nerve dysfunction. Simultaneous bilateral vision loss occurs in about ¼ of cases, and for those who experience sequential loss of vision the medial interval between the first eye and the second is about 8 weeks. In terms of treatment, avoidance of smoking and alcohol likely improve the prognosis. Idebenone started shortly after the onset of symptoms has shown promise in preventing further visual loss. (1) There is also evidence that estrogen might be protective against LHON, which could account for the lower incidence among females. Studies of estrogen replacement therapy for patients with LHON have been encouraging. (2) It is not known whether prophylactic treatment of people who carry a LHON mutation is beneficial.
Another diagnostic consideration is Kjer’s dominant optic neuropathy. This bilateral condition generally has its onset during childhood, unlike in our patient. It has very high penetrance, but the rate of progression and degree of severity can vary widely among people who carry one of the six known mutations responsible for the condition. This is a chromosomal disease that involves proteins that interact with mitochondria. In this respect, it is similar to age-related maculopathy susceptibility 2, a gene that interacts with mitochondria and has variants that increase the risk of age-related macular degeneration.
1. Lyseng-Williamson, KA. Idebenone: A review in Leber’s hereditary optic neuropathy. Drugs 2016;76:805-813.
2. Fantini M, Asanad S, Karanjia R, Sadun AA. Hormone replacement therapy in Leber’s hereditary optic neuropathy: Accelerated visual recovery in vivo. Journal of Current Ophthalmology 2019;31:102-105.