The clinical and genetic spectrum of mitochondrial diseases in China: A multicenter retrospective cross-sectional study.

Mitochondrial diseases (MtDs) present diverse clinical phenotypes, yet large-scale studies are hindered by their rarity. This retrospective, multicenter study, conducted across five Chinese hospitals' neurology departments from 2009 to 2019, aimed to address this gap. Nationwide, 1351 patients were enrolled, with a median onset age of 14.0 (18.5) years. The predominant phenotype was mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) (45.0%). Mitochondrial DNA (mtDNA) mutations were prevalent (87.4%), with m.3243A>G being the most common locus (48.7%). Meanwhile, POLG mutations in nuclear DNA (nDNA) accounted for 16.5%. Comparative analysis based on age groups (with a cut-off at 14 years) revealed the highest prevalence of MELAS, with Leigh syndrome (LS) and chronic progressive external ophthalmoplegia (CPEO) being the second most common phenotypes in junior and senior groups, respectively. Notably, the most commonly mutated nuclear genes varied across age groups. In conclusion, MELAS predominated in this Chinese MtD cohort, underscored by m.3243A>G and POLG as principal mtDNA mutations and pathogenic nuclear genes. The phenotypic and genotypic disparities observed among different age cohorts highlight the complex nature of MtDs.