SYNJ1 and Parkinson disease: Homozygous R258Q and R459P mutations in synaptojanin 1 cause early-onset atypical parkinsonism with PD-like symptoms such as gait disturbances, stiffness, and slowness of movement, along with loss of DAT in the putamen, but unlike PD, show poor responsiveness to levodopa, and cerebral cortex atrophy (Krebs et al., 2013; Quadri et al., 2013; Olgiati et al., 2014; Kirola et al., 2016).