LT may also differentially affect survival, e.g., patients with mtDNA depletion syndromes caused by mutations in DGUOK gene—encoding the mitochondrial deoxyguanosine kinase, which phosphorylates purines to the corresponding nucleotides in the mitochondrial nucleotides salvage pathway—show lower survival than those of patients with other PMD. Here, DGUOK is linked to Pelizeaus-Merzbacher spectrum disorder.