HTR4 and Parkinson disease: A dysregulation of these pathways goes along with the enrichment of significantly altered G protein‐coupled receptors (GPCR) signaling pathways, e.g. serotonin signaling (HTR4/6/7 signaling)28 and dopamine signaling (DRD1/5 signaling)29, both of which are implicated in PD (Fig. 4c; Supplementary Data 6–8).