SYNJ1 encodes synaptojanin 1, a dual-function phosphoinositide phosphatase that plays critical roles in synaptic vesicle recycling and membrane trafficking 1. The protein dephosphorylates various phosphoinositides including PIP2, facilitating clathrin-mediated endocytosis and synaptic vesicle recycling at presynaptic terminals 1. SYNJ1 mutations cause a spectrum of neurological disorders with distinct phenotypes based on mutation type. Complete loss-of-function mutations result in severe developmental and epileptic encephalopathy characterized by neonatal-onset intractable seizures, profound developmental delay, hypotonia, and early death 23. In contrast, missense mutations cause early-onset atypical parkinsonism with features including dystonia, diplopia, and poor levodopa response 45. Recent research suggests SYNJ1 may have neuroprotective functions through interaction with thrombospondin-1 (TSP-1), with decreased SYNJ1 expression observed in Parkinson's disease models 6. Clinically, SYNJ1-related atypical parkinsonism typically presents with earlier onset than typical Parkinson's disease and may respond to specific treatments like clonazepam for dystonic symptoms 45. The protein's role in membrane trafficking dysfunction appears central to disease pathogenesis across the clinical spectrum 1.