One of the most highly downregulated proteins in our proteomic data set was GTP cyclohydrolase I (Gch1, also known in Drosophila as Punch), which is encoded by a gene orthologous to the human Parkinson’s disease GWAS locus GCH1 (Fig. 2, Supplementary Data Set 2). The gene discussed is GCH1; the disease is Parkinson disease.