Deoxynucleoside therapy for diseases caused by unbalanced nucleotide pools including mitochondrial DNA depletion syndromes

The invention relates generally to a pharmacological therapy for human genetic diseases, specifically those characterized by unbalance nucleotide pools, more specifically mitochondrial DNA depletion syndromes, and more specifically, thymidine kinase 2 (TK2) deficiency. The pharmacological therapy involves the administration of at least one deoxynucleoside, or mixtures thereof. For the treatment of TK2 deficiency, the pharmacological therapy involves the administration of either deoxythymidine (dT) or deoxycytidine (dC), or mixtures thereof. This administration of deoxynucleosides is applicable to other disorders of unbalanced nucleotide pools, especially those found in mitochondrial DNA depletion syndrome.