Leber hereditary optic neuropathy (LHON) is a mitochondrial genetic disorder. Unlike most inherited conditions, which involve mutations in DNA stored in the cell’s nucleus, LHON is caused by mutations in mitochondrial DNA, the small, separate genome that exists inside the energy-producing structures of your cells. This distinction matters because mitochondrial DNA follows a completely different inheritance pattern: it passes exclusively from mother to child.
How Mitochondrial Inheritance Works
Every cell in your body contains mitochondria, tiny organelles that generate the energy your cells need to function. These mitochondria carry their own DNA, separate from the 23 pairs of chromosomes you inherited from both parents. Mitochondrial DNA comes only from your mother, because the egg cell provides all the mitochondria for a developing embryo while sperm contribute essentially none.
This means a father with LHON cannot pass the mutation to any of his children. A mother who carries the mutation will pass it to all of her children, both sons and daughters. However, carrying the mutation does not guarantee vision loss. Many carriers live their entire lives without symptoms. The ratio of affected males to females is roughly 3 to 1, and researchers still don’t fully understand why men are more vulnerable. Earlier estimates placed this ratio at 5 to 1, but larger international studies have revised it downward, suggesting older data overrepresented young men.
The Mutations Behind LHON
Over 90% of LHON cases trace back to one of three specific point mutations in mitochondrial DNA. The most common by far is the m.11778G>A mutation, which accounts for 70 to 90% of all cases worldwide. The other two are m.3460G>A and m.14484T>C. All three mutations affect genes that encode parts of complex I, a critical component in the mitochondrial energy production chain.
When complex I doesn’t work properly, mitochondria produce less energy and generate more harmful byproducts called reactive oxygen species. This creates a damaging cycle: impaired mitochondria leak more of these toxic molecules, which in turn cause further damage to the mitochondria themselves. Genetic testing through a simple blood sample can confirm which mutation a person carries.
Why LHON Targets the Optic Nerve
The retinal ganglion cells that form the optic nerve are uniquely dependent on mitochondria. These cells have long, thin projections that carry visual signals from the eye to the brain, and they require enormous amounts of energy to maintain the electrical impulses traveling along those fibers. Because of this extreme energy demand, retinal ganglion cells are far more sensitive to mitochondrial dysfunction than most other cell types in the body.
When the mitochondria in these cells can’t keep up with energy needs, reactive oxygen species accumulate and trigger a self-destruction process called apoptosis. The result is progressive death of retinal ganglion cells, which translates to loss of central vision. Peripheral vision typically remains intact, but the ability to read, recognize faces, and see fine detail deteriorates.
How Vision Loss Progresses
LHON typically strikes between ages 15 and 35, though it can appear outside this range. Vision loss usually begins in one eye as painless blurring of central vision. The second eye follows weeks to months later, and in about 97% of patients, both eyes are affected within a year. Visual acuity generally stabilizes within four to six months of the first symptoms.
The painless nature of LHON is one feature that helps distinguish it from optic neuritis caused by conditions like multiple sclerosis, which typically involves eye pain with movement. The lack of pain, the specific pattern of bilateral involvement, and the young age of onset are clinical clues that point toward LHON rather than other causes of optic nerve damage.
Environmental Factors That Raise Risk
Not every person who carries an LHON mutation develops vision loss, and environmental factors play a significant role in tipping the balance. Smoking is the most clearly established trigger. One large epidemiological study found that the risk of developing disease in male carriers jumped from 50% to 93% in smokers. Smoking directly decreases complex I activity, compounding the genetic defect that already weakens this system.
Both LHON patients and asymptomatic carriers smoke at significantly higher rates than the general population. Heavy alcohol intake has also been associated with increased risk, though the evidence is less definitive than for smoking. For carriers who know their genetic status, avoiding tobacco is one of the few concrete steps that can meaningfully reduce the chance of vision loss.
Treatment Options
A medication called idebenone is approved for treating LHON-related vision loss in people 12 years and older. Idebenone works as a synthetic antioxidant that can bypass the defective complex I in the mitochondrial energy chain, helping cells produce energy through an alternative route while also reducing oxidative damage. Treatment typically lasts a minimum of 24 months. If no clinically relevant recovery occurs within that window, treatment is stopped. Patients who do respond continue until improvement plateaus, up to a maximum of 36 months.
Gene therapy was once considered a promising avenue. A product called Lumevoq, designed to deliver a working copy of the affected gene directly into the eye, underwent clinical trials but failed to demonstrate a significant difference in vision compared to sham injections. The manufacturer withdrew its European marketing application in April 2023 after regulators raised concerns about the evidence.
Recovery rates vary by mutation. Carriers of the m.14484T>C mutation have the highest rates of spontaneous visual recovery, while those with the most common m.11778G>A mutation generally have the poorest visual outcomes. When recovery does occur, it can happen months or even years after the initial vision loss, though it is rarely complete.