GCH1 and Parkinson disease: P/LP variants responsible for the parkinsonian phenotype were found in 17 genes, including 10 known PD-related genes (CHCHD2, DJ-1, GBA, HTRA2, LRRK2, PINK1, PRKN, PLA2G6, SNCA and VPS35) and 7 causative genes of other diseases (ATXN2, ATXN3, DCTN1, GCH1, MAPT, PSEN1 and TH).