SYNJ1 and Parkinson disease: At the moment of writing this manuscript, three homozygous point variants in the 5PPase domain of Synj1 had been described in patients: the Y793C mutation leading to typical levodopa-responsive parkinsonism (Xie et al., 2019), the R800C mutation leading to asymmetric parkinsonism and seizures (Taghavi et al., 2018), and the Y849C mutation leading to early-onset treatment-resistant seizures and progressive neurological decline (numbering based on Synaptojanin1-145 isoform 2) (Hardies et al., 2016; Figure 1).