For example, brain organoids generated from hiPSCs from Parkinson’s (Smits et al., 2019) and Alzheimer’s (Raja et al., 2016) patients recapitulate hallmark disease phenotypes, most notably reduced dopaminergic neurons in Parkinson’s organoids and amyloid beta aggregation and hyperphosphorylated tau protein in Alzheimer’s organoids. This evidence concerns the gene MAPT and Parkinsonism.