Analysis of genetic risk factors in Japanese patients with Parkinson's disease.

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Parkinson's disease (PD) is caused by a combination of genetic and environmental factors. Notably, genetic risk factors vary according to ethnicity and geographical regions, and few studies have analyzed the frequency of PD causative genes in Japanese patients. Therefore, we performed genetic analyses of Japanese patients with PD. We recruited 221 participants, including 26 patients with familial PD. Genetic risk factors were evaluated by target sequencing and gene dosage analysis. We detected the genetic risk factors in 58 cases (26.2%) and classified patients into three groups to clarify the differences in genetic risk factors by age at onset (AAO). The early-onset group (AAO < 50 years) included 18 cases (44.7%), who tended to have a larger number of genetic risk factors than the later-onset groups. Regarding the AAO for each causative gene, patients with PRKN variants were significantly younger at onset than those bearing LRRK2 variants. LRRK2 variants showed similar frequency in each AAO group. Of note, we identified two novel variants. Patients with early-onset PD have more genetic risk factors than patients with late-onset PD. In Japanese patients with PD, PRKN, and LRRK2 were the major PD-related genes. Particularly, LRRK2 was a common genetic factor in all age groups because of the presence of the Asian-specific variant such as LRRK2 p.G2385R. Accumulation of genetic and clinical data can contribute to the development of treatments for PD.