Heteroplasmic Mutant Load Differences in Mitochondrial Disease

Background: Mitochondrial DNA (mtDNA)-associated mitochondrial disease is influenced by mutant pathogenicity and corresponding heteroplasmic loads. However, the manner in which heteroplasmic mutant load affects patient phenotypes and the relationship between mutant types and heteroplasmic mutant loads remain unknown. We aimed to investigate the distribution of the mutant load of different mtDNA mutations in Leigh syndrome.
Methods: We used next-generation sequencing to confirm mtDNA mutations in 31 patients with Leigh syndrome. Subsequently, we counted the number of mtDNA reads to quantitatively analyze the heteroplasmic mutant load. Confirmed cases of mtDNA-associated Leigh syndrome were classified according to the mutations.
Results: We discovered that MT-ATP6 was the most commonly mutated gene, followed by MT-ND3 and MT-ND5. MT-ATP6 had a significantly higher mutant load than MT-ND3 and MT-ND5. By contrast, MT-ND5 had a significantly lower mutant load than MT-ND3. Notably, the mutation loads varied significantly among patients carrying the MT-ATP6, MT-ND3, and MTND5 mutations.
Conclusions: Our study illustrated the heteroplasmic diversity and phenotypic expression threshold of mutated mitochondrial genes in mtDNA-associated Leigh syndrome. The results provide promising insights into the genotype-phenotype correlation in mtDNA-associated Leigh syndrome that are expected to guide the development of tailored treatments for Leigh syndrome.