Homoplasmic deleterious MT-ATP6/8 mutations in adult patients

Area of Science:

• Biochemistry
• Genetics
• Mitochondrial Diseases

Background:

• Complex V (ATP synthase) is crucial for cellular energy production.
• Defects in mitochondrial genes, such as MT-ATP6/8, can lead to severe clinical manifestations.
• Understanding the pathogenicity of novel mutations is essential for accurate diagnosis.

Purpose of the Study:

• To systematically sequence MT-ATP6/8 genes in a cohort of patients to identify mutations.
• To functionally characterize identified mutations to determine their impact on Complex V function.
• To assess the diagnostic utility of different cellular models (muscle, fibroblasts, cybrids) for Complex V defects.

Main Methods:

• Systematic sequencing of MT-ATP6/8 genes in 512 patients.
• Functional analysis of mutations in patient-derived muscle and fibroblasts, and in transmitochondrial cybrids.
• Biochemical assays including spectrophotometry for oxidative phosphorylation, Western blotting, ATP production, glycolysis, and cell proliferation assays.

Main Results:

• Identified 27 putative homoplasmic mutations in MT-ATP6/8 genes.
• Demonstrated the deleterious nature of three novel mutations through functional analyses.
• Observed significant variations in mutation severity and cellular model responses, indicating tissue-specific effects.

Conclusions:

• The study confirms three novel mutations in MT-ATP6/8 as pathogenic, contributing to Complex V deficiency.
• Differences in functional consequences across muscle, fibroblasts, and cybrids highlight the complexity of assessing mitochondrial mutations.
• The findings suggest a potential under-diagnosis of human Complex V defects due to variability in mutation impact and diagnostic models.