Among these approaches, supplementation of deoxyribonucleosides (dNs) has been proposed as a powerful strategy for the treatment of MDSs caused either by defective nucleotide metabolism (such as RRM2B and MPV17-related diseases) or an impairment of the mtDNA synthesis machinery (such as POLG-related diseases) [12,43,44,45]. The gene discussed is MPV17; the disease is glycogen storage disease VI.