COMT and Parkinson disease: Various clinical phenotypes exist within the PD spectrum, and both medication response and motor complication risk have been proposed as distinguishing features of such phenotypes.31 Pharmacogenetic variation throughout the levodopa pathway (eg, in the cathechol‐o‐methyltransferase [COMT] gene) has also been suggested to predict medication response and motor complication risk.32 Another contributing factor may be that greater benefit from treatment encourages concordance, increasing exposure to levodopa and its complications.