Mutations in the TK2 gene result in a decrease of enzyme activity which impairs recycling of mtDNA nucleotides and finally causes progressive muscle weakness (myopathy) and mitochondrial DNA depletion syndrome 2 (myopathic type, MIM 609560) (Cámara et al. 2015; Saada et al. 2001; Wang et al. 2003). This evidence concerns the gene TK2 and myopathy.