DGUOK and mitochondrial DNA depletion syndrome: Mitochondrial DNA depletion syndrome (MDS) is a group of severe, phenotypically heterogeneous, recessively inherited disorders characterized by marked reduction of the mtDNA content in affected tissues and organs.[1] Deoxyribonucleoside kinase (DGUOK) mutation is the major causes of hepatocerebral form MDS, accounting for ≈20% of all MDS cases, and is most common genetic factor of hepatic MDS.[2] DGUOK mediates the phosphorylation of deoxyguanosine and deoxyadenosinepurine into the corresponding nucleotides in mitochondria.