Congenital or late-onset myopathy in patients with the T14709C mtDNA mutation

Area of Science:

• Genetics
• Mitochondrial Biology
• Neuromuscular Disorders

Background:

• Mitochondrial DNA (mtDNA) mutations are implicated in various human diseases.
• The tRNAGlu gene plays a crucial role in mitochondrial protein synthesis.
• Point mutations in mtDNA can lead to diverse clinical presentations.

Purpose of the Study:

• To investigate the clinical and molecular characteristics of patients with a specific mtDNA mutation.
• To correlate genotype with phenotype in mitochondrial myopathies.
• To identify potential diagnostic clues for this mtDNA mutation.

Main Methods:

• Clinical assessment of three patients with distinct phenotypes.
• Muscle biopsy analysis, including cytochrome c oxidase (COX) staining and ragged-red fibers (RRFs) assessment.
• Biochemical assays of mitochondrial respiratory chain complex activities.
• Mutation analysis of mtDNA, quantifying T14709C mutation levels in different tissues.

Main Results:

• All three patients shared the T14709C point mutation in the tRNAGlu gene of mtDNA.
• Phenotypes ranged from severe congenital myopathy with respiratory distress to slowly progressive myopathy with diabetes mellitus.
• Muscle biopsies revealed COX-negative RRFs and reduced activities of mitochondrial respiratory chain complexes I, III, and IV.
• The T14709C mutation was highly abundant in muscle tissue but less prevalent in other accessible tissues.
• Previously reported patients with this mutation also exhibited myopathy, supporting a consistent genotype-phenotype correlation.

Conclusions:

• The T14709C mutation in the tRNAGlu gene of mtDNA is associated with mitochondrial myopathy.
• Clinical manifestations can vary from congenital to late-onset forms.
• The presence of diabetes mellitus is a significant clinical feature and a potential indicator for molecular diagnosis of this mutation.