Point mutations in the gene encoding TK2 are correlated with mtDNA disorders in a heterogeneous group of patients suffering from the so-called mtDNA depletion syndrome (MDS), which is a syndrome with symptoms resembling those of AIDS patients treated with nucleoside analogues, but the mechanisms behind these mitochondrial effects are still not well understood [31]–[33]. Here, TK2 is linked to mitochondrial DNA depletion syndrome.