As a result of TP dysfunction, MNGIE patients accumulate both dThd and dUrd in plasma and in tissues with a subsequent reduction of cytidine triphosphate (dCTP), which causes nucleoside and nucleotide pool imbalance and disrupts the equilibrium of intra-mitochondrial deoxyribonucleoside triphosphate (dNTP) pools [3,4]. Here, TYMP is linked to mitochondrial neurogastrointestinal encephalomyopathy.