Loss-of-function mutations in MGME1 impair mtDNA replication and cause multisystemic mitochondrial disease

Area of Science:

• Genetics
• Molecular Biology
• Mitochondrial Biology

Background:

• Mitochondrial DNA (mtDNA) maintenance disorders arise from defects in replication or nucleotide biosynthesis.
• The genetic causes for many mtDNA maintenance disorders remain unknown.
• Previous research focused on known replication machinery and nucleotide pathways.

Purpose of the Study:

• To identify the genetic basis of an unknown mitochondrial syndrome.
• To investigate the function of the C20orf72 gene in mtDNA maintenance.

Main Methods:

• Genetic analysis of affected families to identify mutations.
• Biochemical assays to determine the enzymatic activity of C20orf72 (MGME1).
• Cellular studies using patient fibroblasts and MGME1-depleted cells to assess mtDNA replication and processing.

Main Results:

• Identified homozygous mutations in C20orf72 in three families with a severe mitochondrial syndrome.
• C20orf72 encodes MGME1, a mitochondrial RecB-type exonuclease with DNA processing capabilities.
• MGME1 deficiency leads to mtDNA depletion, deletions, stalled replication intermediates, and increased 7S DNA levels.

Conclusions:

• MGME1 is essential for mitochondrial genome maintenance.
• Mutations in C20orf72 (MGME1) cause a novel mitochondrial DNA maintenance disorder.
• MGME1's role in processing DNA substrates is critical for mtDNA stability.