BACKGROUND AND OBJECTIVES: The mitochondrial DNA (mtDNA) genes METHODS: Clinical, biochemical, and molecular genetics data of patients with genetically confirmed RESULTS: A cohort of 111 patients, 98 unreported, were analyzed (55 male, 56 female). Patients had infantile-onset disease (<
1 year) in 44% of cases, pediatric-onset (≥1 year and ≤12 years) in 36%, and late-onset (>
12 years) in 20%. Kaplan-Meier analysis showed a significant difference ( DISCUSSION: Our results define a more accurate classification based on the age at onset for MT-ATPase deficiency and provide fundamental clinical and biochemical data for disease management.