LHON is the world’s most prevalent mitochondrial disease and an important cause of inherited blindness in young adults. Resulting from inherited mitochondrial DNA mutations, LHON causes sudden, usually irreversible vision loss, profoundly impacting a patient’s autonomy and quality of life.
LHON begins unexpectedly, without warning or pain. Vision loss usually starts in one eye, manifesting as a defect in central vision.
The second eye is usually affected within weeks to a few months of the first. As the disease progresses, the visual defect expands, eventually leaving only limited peripheral vision. Most people with LHON reach legal blindness within one year of the onset of vision loss.
Vision loss often strikes in the prime of life, upending educational or career plans and undermining autonomy. The disruption places a high emotional toll on patients and their families, including relatives who carry the mutation. LHON is also associated with higher rates of smoking and excessive alcohol use.
LHON is linked to mutations in mitochondrial genes, primarily point mutations in the ND1, ND4 and ND6, with the ND4 mutation (m.11778G>A) accounting for approximately 70% of cases globally. These genes encode subunits of Complex I, an enzyme complex that plays a critical role in energy production within mitochondria, the structures that power the cells.
When Complex I is disrupted, cellular respiration is impaired, resulting in a buildup of reactive oxygen species. The oxidative stress leaves the cell vulnerable to metabolic disruption, damage and ultimately cell death.
Retinal ganglion cells, located in the innermost layer of the retina, require substantial energy to process and transmit visual information to the brain. Deprived of energy and damaged by oxidative stress, these cells lose the ability to propagate visual signals along their fibers, which form the optic nerve. The cells’ degeneration results in rapid, usually irreversible loss of vision.
First described in the 19th century, LHON has evolved from clinical description to a mitochondrial genetic understanding. Today it is recognized as the most common inherited mitochondrial disease and a benchmark condition in neuro-ophthalmology.
There is currently no approved therapy that prevents or reverses vision loss in LHON patients. The only approved therapy, idebenone, is available only in some markets. Research continues to pursue effective treatments for a population with high unmet need.
Diagnosis is confirmed by genetic testing for mitochondrial DNA variants (most commonly in the ND1, ND4, ND6 genes). Suspected cases should be referred to a neuro-ophthalmologist for definitive diagnosis. Early recognition helps patients access low-vision resources and clinical research opportunities.
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