The spinocerebellar ataxias

The spinocerebellar ataxias (SCAs) are diseases characterized by the progre ssive degeneration and subsequent loss of neurons accompanied by reactive g liosis, degeneration of fibers from the deteriorating neurons, and clinical symptoms reflecting the locations of the lost neurons. The degenerative ch anges affect specific neuronal groups while others remain preserved, and th ese diseases can therefore be viewed as system degenerations. The SCAs resu lt from either genetically transmitted diseases with dominant inheritance o r unknown causes with sporadic occurrence. Most of these disorders affect t he cerebellum and its pathways, resulting in progressive deterioration of c erebellar function manifested by increasing unsteadiness of gait, incoordin ation of limb movements with impairment of skilled movements such as handwr iting, and a distinctive dysarthria. Other neuronal systems are affected in some of the se disorders, notably the corticospinal pathway, basal ganglia , and autonomic nuclei of the brain stem and spinal cord.