SLC22A1 and Parkinson disease: There are two possible explanations for this association: (i) it is possible that the rs622342 C allele accounts for a reduced anti-Parkinson drug uptake by the small intestine and hence is responsible for a lower bioavailability [65]; (ii) OCT1, which is expresses at low levels in the brain, can act as rate-limiting step for drug uptake by this target tissue.