Unusual adult-onset Leigh syndrome presentation due to the mitochondrial m.9176T>C mutation

► Leigh syndrome (LS) is an incurable neurodegenerative pediatric disorder that results from respiratory chain failure. ► LS is associated with mutations in ATP6 and ATP8 mitochondrial genes (mtDNA). ► We describe clinical and molecular features of a young woman with an unusual adult-onset LS while her brother died at a young age. ► The homoplasmic m.9176T→C mutation was found in her muscle-extracted mtDNA. ► This novel case report and literature review highlights the variability of phenotypic expression of the m.9176T→C mutation.