Here, we summarise the evidence on the prodromal phase of PD in patient groups at increased of PD with well described prodromal features: patients with idiopathic rapid eye movement (REM) sleep behaviour disorder (RBD), patients with idiopathic anosmia and families with monogenic mutations that are closely linked to PD pathology, in particular the Leucine‐rich repeat kinase 2 gene (LRRK2) and glucocerebrosidase gene (GBA). The gene discussed is GBA1; the disease is Parkinson disease.