brain, spinal cord, and nerve disorders
Spinal Muscular Atrophies (SMAs)
Introduction
Spinal muscular atrophies are hereditary disorders in which nerve cells that originate in the spinal cord and brain stem degenerate, causing progressive muscle weakness and wasting. The five main types of spinal muscular atrophies cause various degrees of muscle weakness and wasting. Depending on the type, people may be confined to a wheelchair, and life span may be shortened. The diagnosis, suggested by symptoms, is based on family history, tests of muscle and nerve function, and blood tests to detect the defective gene. There is no cure, but physical therapy and use of braces can help. (See also Overview of the Peripheral Nervous System .) Spinal muscular atrophies are usually inherited as an autosomal (not sex-linked) Recessive disorders . That is, two genes for the disorder, one from each parent, are required for the person to have inherited the disorder. These disorders may affect the brain and spinal cord (central nervous system), as well as peripheral nerves. There are five main types of spinal muscular atrophy. 