GCH1 and Parkinson disease: In this study, we determined the mutational spectrum of 20 known PD‐associated genes in a cohort of Kinh Vietnamese patients diagnosed with EOPD, and identified 37 out of 83 (45%) patients carrying variants in LRRK2, PRKN, EIF4G1, ATP13A2, GBA1, DNAJC6, PINK1, DNAJC13, MAPT, VPS13C, DJ‐1, FBXO7, GCH1, PLA2G6, and VPS35.