SEPTIN3 is a filament-forming cytoskeletal GTPase that plays roles in cell division and cytoskeletal organization 1. As a septin family member, it forms organized supramolecular structures at synapses that are critical for synaptic transmission and function 2. In disease pathology, SEPTIN3 has emerged as a novel autoantibody target in paraneoplastic cerebellar ataxia, with autoantibodies identifying patients with progressive cerebellar syndromes associated with melanoma and small cell lung cancer 1. Additionally, anti-SEPTIN3 antibodies have been identified in autoimmune cerebellar ataxia patients 3. In Alzheimer's disease, SEPTIN3 levels are altered in affected brain regions; synaptic SEPTIN3 accumulation correlates strongly with complement deposition (C1q) and synapse loss in disease models 2. Notably, septin-3 levels positively correlate with preserved cognitive function 4, and altered septin-3 expression was identified as a novel proteomic signature in AD brains 5. Clinically, SEPTIN3 has emerged as a candidate biomarker: it was identified as a Tier 2 protein associated with adenocarcinoma development 6, a discriminant protein in maternal smoking during pregnancy 7, and a component of a five-gene prognostic signature for triple-negative breast cancer risk stratification 8.