The m.8344A>G mutation in the MTTK gene, which encodes the mitochondrial transfer RNA for lysine, is traditionally associated with myoclonic epilepsy and ragged-red fibres (MERRF), a multisystemic mitochondrial disease that is characterised by myoclonus, seizures, cerebellar ataxia, and mitochondrial myopathy with ragged-red fibres.
Deficiency in TK2 activity due to genetic alterations causes devastating mitochondrial diseases, which are characterized by mitochondrial DNA (mtDNA) depletion or multiple deletions in the affected tissues.