Autosomal dominant spastic paraplegia type 9A (SPG9A) is a rare, inherited neurological disorder characterized by progressive spasticity (stiffness) and weakness of the legs. It is caused by mutations in the KIF5A gene, which is responsible for the production of a protein involved in the transport of molecules within cells. Symptoms typically begin in childhood or adolescence and may include difficulty walking, stiffness in the legs, and weakness in the lower limbs. Other symptoms may include bladder and bowel dysfunction, speech difficulties, and cognitive impairment. Treatment is supportive and may include physical therapy, medications, and assistive devices.