A functionally dominant mitochondrial DNA mutation.

Area of Science:

• Genetics
• Molecular Biology
• Biochemistry

Background:

• Mitochondrial DNA (mtDNA) tRNA gene mutations typically exhibit recessive inheritance, requiring high heteroplasmy levels (70-90%) for clinical manifestation.
• This recessive nature is attributed to the need for significant disruption of the respiratory chain (RC) to produce a phenotype.

Purpose of the Study:

• To report a novel mtDNA mutation that presents a dominant inheritance pattern, contradicting the established recessive model.
• To investigate the mechanism and implications of a dominant mtDNA mutation causing severe multisystem disorder at low heteroplasmy levels.

Main Methods:

• Studied a 13-year-old boy with clinical, radiological, and biochemical evidence of mitochondrial disorder.
• Detected a novel heteroplasmic C>T mutation at mtDNA nucleotide 5545 using molecular analysis.
• Determined the pathogenic threshold of the mutation in cybrids.

Main Results:

• Identified a novel heteroplasmic C>T mutation in the tRNA(Trp) gene at mtDNA 5545, causing disease at <25% heteroplasmy.
• Established a pathogenic threshold between 4-8% heteroplasmy in cybrids, indicating a dominant mechanism.
• The mutation affects the anticodon triplet's central base, potentially altering tRNA(Trp) codon specificity and impairing RC function.

Conclusions:

• Introduced the concept of dominant inheritance in mitochondrial genetics, challenging the traditional recessive model.
• Highlighted new diagnostic challenges due to dominant mtDNA mutations potentially escaping detection at low heteroplasmy.
• Suggested that stochastic accumulation of similar dominant mutations during aging could impair cellular RC function.