SYNJ1 and Parkinson disease: Another risk factor for PD that is associated with lipid metabolism is Synaptojanin 1 (SYNJ1), which is a PIP-phosphatase (Krebs et al., 2013; Quadri et al., 2013; Olgiati et al., 2014; Ben Romdhan et al., 2018; Schechter and Sharon, 2021).