XDH and Parkinson disease: While xanthines have been linked to multiple molecular mechanisms in PD, including the generation of reactive oxygen species by xanthine oxidase and the inhibition of the adenosine A2A receptor and Monoamine Oxidase type B (see section on “Xanthine metabolites”), the observed sub-network alteration involving decreased HPRT1 expression suggests an additional mechanism by which xanthines may influence PD.