GBA1 and Parkinson disease: As an example of this, scRNA-seq data from hiPSC-derived dopamine neurons from healthy and Parkinson’s disease (PD) patients with mutations to the GBA gene have been used to study the progression of molecular phenotypes using the Ouija algorithm, a semi-supervised method that uses expression switches of a small set of predefined marker genes to infer the pseudotime trajectory [118,119].