KIF21B is a plus-end-directed processive kinesin motor protein that regulates microtubule dynamics and neuronal morphology 1. It controls microtubule growth rate and catastrophe frequency, restricting microtubule length and enabling rapid cytoskeletal remodeling in neurons and T cells 12. KIF21B is essential for dendritic arbor complexity, dendritic spine formation, and synaptic transmission 1. It facilitates GABA(A) receptor trafficking and is critical for learning and memory; Kif21b-null mice exhibit cognitive deficits 1. Functionally, KIF21B maintains its activity through autoinhibition mechanisms; disruption of this autoregulation causes pathogenic effects 3. Dysregulation of KIF21B associates with multiple neurological and developmental disorders. Missense variants and duplications cause neurodevelopmental disorders with brain malformations including corpus callosum agenesis and microcephaly through impaired neuronal migration and axonal growth 3. KIF21B variants were identified as novel candidate genes for late-onset Parkinson's disease 45. Elevated KIF21B expression correlates with accelerated neurodegeneration in Alzheimer's disease and multiple sclerosis 6. Additionally, KIF21B variants are associated with ocular congenital cranial dysinnervation disorders 7. In osteosarcoma, KIF21B upregulation promotes cell proliferation through the PI3K/AKT pathway 8.