A mitochondrial tRNA aspartate mutation causing isolated mitochondrial myopathy.

Area of Science:

• Genetics
• Mitochondrial Biology
• Neurology

Background:

• Mitochondrial myopathies are a group of inherited disorders caused by mutations in mitochondrial DNA (mtDNA) or nuclear DNA.
• Mutations in mitochondrial transfer RNA (tRNA) genes are a known cause of mitochondrial myopathy, often presenting with exercise intolerance and muscle weakness.

Observation:

• A young girl exhibited severe exercise intolerance, with decreased anaerobic threshold and maximal oxygen consumption.
• Muscle biopsy revealed ragged red fibers and decreased activity of mitochondrial respiratory chain complexes I and IV.
• Genetic analysis identified a heteroplasmic A to G transition at nucleotide position 7526 in the mitochondrial tRNA Aspartate (tRNA(Asp)) gene in multiple tissues.

Findings:

• The identified mutation in the mt tRNA(Asp) gene represents a new genetic cause for mitochondrial myopathy.
• The mutation was heteroplasmic and not detected in the patient's mother, suggesting a de novo occurrence or low-level transmission.
• The patient's presentation of combined complex I and IV deficiency is linked to this specific tRNA mutation.

Implications:

• This case expands the genetic spectrum of mitochondrial myopathies.
• Highlights the importance of sequencing all mitochondrial tRNA genes, including less common ones like mt tRNA(Asp), in affected tissues (muscle) rather than solely in blood for accurate diagnosis.
• Emphasizes the diagnostic value of targeted genetic testing in cases of unexplained mitochondrial dysfunction and exercise intolerance.