Definition of Spinal muscular atrophy
Spinal muscular atrophy is a group of inherited diseases that cause progressive muscle degeneration and weakness, eventually leading to death.
Causes, incidence, and risk factors
Spinal muscular atrophy (SMA) is a collection of different muscle diseases. Grouped together, it is the second leading cause of neuromuscular disease. Most of the time, a person must get the defective gene from both parents to be affected. Approximately 4 out of every 100,000 people have the condition.
Infants with SMA type I are born with very little muscle tone, weak muscles, and feeding and breathing problems. With SMA type III, symptoms may not appear until the second year of life.
Signs and tests
The health care provider will take a careful history and perform a brain/nervous system (neurologic) examination to find out if there is:
There is no treatment for the progressive weakness caused by the disease. Supportive care is important. Attention must be paid to the respiratory system because affected people have difficulty protecting themselves from choking. Breathing complications are common.
The lifespan in SMA type I is seldom longer than 2 – 3 years. Survival time with type II is longer, but the disease kills most of those affected while they are still children. Children with type III disease may survive into early adulthood. However, people with all forms of the disease have worsening weakness and debility.
Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine; Daniel B. Hoch, PhD, MD, Assistant Professor of Neurology, Harvard Medical School, Department of Neurology, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. – 3/9/2010