SNCAIP (synuclein alpha interacting protein) is a neuron-expressed protein that functions as a regulator of protein ubiquitination and degradation pathways implicated in Parkinson's disease pathogenesis. SNCAIP isoform 2 inhibits the ubiquitin ligase activity of SIAH1, preventing proteasomal degradation of target proteins and modulating alpha-synuclein (SNCA) monoubiquitination by SIAH1. The protein localizes to synaptic compartments including presynaptic membranes and synaptic vesicles, consistent with roles in dopamine metabolism and neurotransmitter secretion regulation 1. SNCAIP shows highest expression in brain tissues and lung, with multiple conserved splice variants identified across species 2. Functionally, SNCAIP interacts with SNCA and forms part of critical protein interactomes in neurodegeneration 3. Clinically, SNCAIP is implicated in late-onset Parkinson's disease through rare deleterious variants; disrupting mutations show significant excess in PD cases, and co-inheritance of multiple rare variants in SNCAIP and related genes predicts disease occurrence with high specificity 45. SNCAIP is also involved in aberrant alternative splicing events in PD patients 6. Additionally, SNCAIP duplication has been associated with medulloblastoma predisposition through PRDM6 induction 78.