GCH1 and Parkinson disease: This module also contained the PD variant-associated gene GCH1 (GTP cyclohydrolase 1) that is known to co-express with TH (tyrosine hydroxylase, the enzyme responsible for converting tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA) in the dopamine synthesis pathway) to enhance dopamine production and enable recovery of motor function in rat models of PD34.