Classical MERRF phenotype associated with mitochondrial tRNA(Leu) (m.3243A>G) mutation

Area of Science:

• Genetics
• Neurology
• Mitochondrial Biology

Background:

• Myoclonic epilepsy with ragged red fibres (MERRF) and mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS) are distinct mitochondrial encephalopathies.
• MERRF is typically associated with mutations in the mitochondrial tRNA(Lys) gene, while MELAS is often linked to the m.3243A>G mutation in the tRNA(Leu) gene.

Observation:

• A 13-year-old patient presented with classical MERRF symptoms, including myoclonic epilepsy, ragged red fibres on muscle biopsy, and basal ganglia MRI abnormalities.
• The patient did not exhibit typical MELAS clinical features such as stroke-like episodes or lactic acidosis.
• Genetic analysis revealed the m.3243A>G mutation (typically associated with MELAS) as the cause of the patient's MERRF phenotype.

Findings:

• The m.3243A>G mutation, usually causative of MELAS, can present as a classical MERRF phenotype.
• This case demonstrates significant phenotypic variability within mitochondrial encephalopathies, particularly in juvenile-onset cases.

Implications:

• Comprehensive genetic investigation is crucial for diagnosing suspected mitochondrial diseases, even when clinical presentation is atypical.
• Understanding the broad phenotypic spectrum of mitochondrial mutations aids in accurate diagnosis and patient management.
• This finding expands the known genotype-phenotype correlations for mitochondrial encephalopathies.