Leber Hereditary Optic Neuropahty (LHON)

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LHON is an inherited form of vision loss that can result in sudden, painless loss of central vision due to optic nerve atrophy.  Blurring and clouding of vision are usually the first symptoms of LHON onset.  These vision problems may begin in one eye, or simultaneously in both eyes.  If vision loss starts in one eye, the other eye is usually also affected several weeks or months later.  Within a few months the central vision loss is profound and the individual is legally blind, unable to read without magnification, drive or recognize faces, but some peripheral vision generally remains.  Vision loss results from the death of cells in the optic nerve fibers that relay visual information between the eyes and the brain.  Some optic nerve fibers can get sick and stop functioning, then return to health and some vision can return in a small percentage of cases.  Males are affected more often than females, as about 25% of those affected are females.  Among affected males, about half are ages 14-26 when vision loss occurs, while the other half are younger or older with onset reported as late as age 87.  Onset of vision loss in women carrying a LHON mutation happens at any age, with no distinct peak as with males.  Some individuals carrying a LHON mutation experience symptoms such as tremors, neuropathy and migraine, and are described as LHON Plus.

Genetic testing for LHON requires a simple blood draw. LHON is rare and follows a maternal inheritance pattern, meaning that the mutation is passed down via mitochondrial mitochondria by the mother only. Mutations in the MT-ND1, MT-ND4, MT-ND4L, or MT-ND6 gene can cause LHON. These genes are found in the DNA of cellular structures called mitochondria, which convert the energy from food into a form that cells can use. A significant percentage of people with a mutation that causes LHON do not develop any features of the disorder. Specifically, more than 50 percent of males with a mutation and more than 85 percent of females with a mutation never experience vision loss or related health problems. Additional factors may determine whether a person develops the signs and symptoms of this disorder. Environmental factors such as smoking and alcohol use may be involved, although studies have produced conflicting results. Researchers are also investigating whether changes in additional genes contribute to the development of signs and symptoms. Genetic counseling is recommended.

Management of affected individuals is largely supportive, with the provision of visual aids, help with occupational rehabilitation, and registration with the relevant social services. ECG may reveal a pre-excitation syndrome in individuals harboring a mtDNA LHON-causing pathogenic variant; referral to cardiology can be considered and treatment for symptomatic individuals is the same as that in the general population. A multidisciplinary approach for those affected individuals with extraocular neurologic features (ataxia, peripheral neuropathy, nonspecific myopathy, and movement disorders) should be considered to minimize the functional consequences of these complications.

Individuals harboring a mtDNA LHON-causing pathogenic variant should be strongly advised to moderate their alcohol intake and not to smoke. Avoiding exposure to other putative environmental triggers for visual loss, in particular industrial toxins and drugs with mitochondrial-toxic effects, also seems reasonable.