XDH and Parkinson disease: Interestingly, in an open-label, single-arm trial, 26 PD patients received a combined treatment with inosine and an inhibitor of the enzyme XDH that converts hypoxanthine to xanthine (see Fig. 6, left side), and this treatment increased blood hypoxanthine and ATP levels, and lowered the patients’ UPDRS III motor impairment score74.