Leigh Syndrome Awareness Day Date in the current year: September 17, 2025

Also known as Leigh’s disease or subacute necrotizing encephalomyelopathy, Leigh syndrome was named after British neuropsychiatrist Archibald Denis Leigh, who first described it in 1951. It belongs to a group of disorders called mitochondrial diseases. Mitochondria are organelles present in nearly all cells of the body except red blood cells. Their main task is to generate energy for the cell by converting energy from food into a substance called adenosine triphosphate (ATP), which powers cells. If mitochondria do not function properly, cells do not receive enough energy, which often results in severe health issues.

Leigh syndrome develops due to mutations in either mitochondrial DNA (20-25% of cases) or nuclear DNA that encodes mitochondrial proteins (75-80% of cases). Mitochondrial DNA mutations are passed down from the mother, while nuclear DNA mutations are inherited in an autosomal recessive pattern. This means a child must inherit a copy of the mutated gene from each parent. There is also a type of Leigh syndrome with an X-linked recessive inheritance pattern that mostly affects boys with a carrier mother. More than 100 mutations associated with Leigh syndrome have been identified.

Leigh syndrome is a rare disease that occurs in approximately one out of every 40,000 live births. However, its actual prevalence may be higher due to underdiagnosis. The disease is more prevalent in the Saguenay—Lac-Saint-Jean region of Quebec due to a combination of the founder effect and genetic isolation.

Leigh syndrome is a severe neurodegenerative disorder that causes patients to lose the ability to walk, talk, and swallow. Symptoms typically appear between 3 months and 2 years of age, though later onset in adolescence or adulthood has also been reported. The early signs and symptoms are not specific to Leigh syndrome, making it difficult to diagnose in the early stages. They include poor feeding, lack of age-appropriate weight gain, diarrhea, vomiting, lethargy, and continuous crying or and irritability.

Later symptoms may include neurological issues (muscle weakness, developmental delay, and loss of skills), motor problems, respiratory issues, cardiac issues, cognitive impairment, intellectual disability, mood swings, vision problems, seizures, gastrointestinal issues, and poor growth and weight gain (failure to thrive).

The severity and progression of Leigh syndrome can vary greatly among individuals because there are many types of the disease caused by different mutations. Currently, there is no cure for Leigh syndrome, and the prognosis is typically poor. Some patients die in childhood, while others survive to adolescence but face significant challenges throughout their lives. Treatment focuses on slowing the progression of the disease and improving quality of life.

Leigh Syndrome Awareness Day was established in 2024 by the Cure Mito Foundation, a U.S.-based nonprofit organization that advances research to find cures for Leigh syndrome and, ultimately, mitochondrial disease in general.