"Myo-neuropathy" is commonly associated with mitochondrial tRNA^Lysine mutation

Area of Science:

• Genetics
• Neurology
• Mitochondrial Biology

Background:

• Mitochondrial tRNA^Lys (mt-tRNA^Lys) mutations are linked to myoclonic epilepsy and ragged-red fibers (MERRF).
• Understanding the clinical spectrum and genetic basis of these mutations is essential for accurate diagnosis and management.

Purpose of the Study:

• To analyze clinical, laboratory, morphologic, and molecular findings in East China mt-tRNA^Lys mutation carriers.
• To determine the prevalence of different mutations and their associated phenotypes.

Main Methods:

• Retrospective analysis of 22 mt-tRNA^Lys mutation carriers from a local database.
• Clinical assessment, laboratory tests, morphological examination, and molecular genetic analysis.

Main Results:

• Identified 13 symptomatic and 9 asymptomatic individuals. Common mutations include m.8344 A>G (81.8%).
• High heteroplasmy levels observed in both symptomatic (mean 64.5%) and asymptomatic (mean 53.1%) individuals.
• Frequent symptoms: muscle weakness, exercise intolerance, elevated creatine kinase, peripheral neuropathy, and cerebellar ataxia. Myoclonus was infrequent (23.1%).
• Mitochondrial myopathy (MM) and NARP/NARP-like syndromes were common (77%), while classic MERRF was rare (23%).
• Over one-third of patients lacked central nervous system involvement, suggesting mt-tRNA^Lys gene investigation for 'pure' mitochondrial myo-neuropathy.

Conclusions:

• mt-tRNA^Lys mutations present a broader clinical spectrum than previously recognized, often manifesting as mitochondrial myopathy or neuropathy.
• The classic MERRF phenotype is not the predominant presentation in this East China cohort.
• Investigating the mt-tRNA^Lys gene is vital for patients with 'pure' mitochondrial myo-neuropathy, even without overt neurological signs.