Sonlicromanol is an investigational medication being studied in this trial. It is being tested to see if it can help reduce physical fatigue and improve muscle strength and balance in adults with a specific genetic condition affecting their mitochondria (the parts of cells that produce energy). This medication is being compared to a placebo to determine if it is effective and safe for treating symptoms related to this genetic variant.

Placebo is an inactive substance that looks like the real medication but contains no active treatment. It is used in this study to compare against sonlicromanol to help researchers understand whether any improvements seen are due to the actual medication or other factors.

Primary Mitochondrial Disease with Mitochondrial DNA 3243A>G variant – This is a genetic disorder caused by a specific mutation in the mitochondrial DNA at position 3243, where adenine is replaced by guanine. Mitochondria are the energy-producing structures within cells, and when they do not function properly due to this genetic change, various body systems can be affected. The disease can appear in different forms depending on which organs are most impacted by the faulty mitochondria. Symptoms may develop at any age and can vary widely between individuals, even within the same family. The condition is inherited through the mother, as mitochondrial DNA is passed down only from the maternal line. Over time, the disease may progress as more cells are affected by the malfunctioning mitochondria.

Maternally Inherited Diabetes and Deafness – This condition is one of the forms associated with the mitochondrial DNA 3243A>G mutation, characterized primarily by diabetes and hearing loss. The diabetes typically develops in adulthood and occurs because the insulin-producing cells in the pancreas require large amounts of energy and are particularly vulnerable to mitochondrial dysfunction. Hearing loss usually affects both ears and tends to worsen gradually over time. The condition may also affect other body systems to varying degrees, though diabetes and deafness are the main features. Symptoms usually appear between the ages of 20 and 40 years.

Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like Episodes – This is a severe form of mitochondrial disease that affects multiple body systems, particularly the brain and muscles. Individuals experience episodes that resemble strokes, causing sudden weakness, vision problems, or seizures, though these are not caused by blocked blood vessels like typical strokes. The brain and muscles accumulate lactic acid due to impaired energy production, leading to fatigue, muscle weakness, and exercise intolerance. Additional symptoms may include headaches, vomiting, and difficulty with coordination and movement. These stroke-like episodes can occur repeatedly and may lead to progressive neurological decline over time.