As such, HSP-related KIF1A mutants, whether loss-of-function or gain-of-function, may result in misdelivery of Syt-IV, thereby dysregulating synaptic vesicle fusion and release of a variety of neurotrophins, altering LTP, and leading to downstream effects such as learning and memory defects, problems with motor control, and other brain region specific effects. Here, KIF1A is linked to hereditary spastic paraplegia.