Spastin is an ATP-dependent microtubule severing protein. Microtubule severing may promote reorganisation of cellular microtubule arrays and the release of microtubules from the microtubule organising centre following nucleation. In humans, defects in spastin are the cause of spastic paraplegia autosomal dominant type 4 (SPG4). Spastic paraplegia is a neurodegenerative disorder characterised by a slow, gradual, progressive weakness and spasticity of the lower limbs.