To explore the potential use of iPSC-derived neurons in detecting protein accumulation and aggregation phenotypes, we selected two PD-causing genotypes: the homozygous G2019S point mutation in the LRRK2 gene, which causes autosomal-dominant PD, and the heterozygous triplication of the SNCA locus (total: four functional gene copies), which also causes autosomal-dominant PD. The gene discussed is SNCA; the disease is Parkinson disease.