Spinal muscular atrophy is a group of inherited diseases that cause progressive muscle degeneration and weakness, eventually leading to death.
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.
The most severe form is SMA type I, also called Werdnig-Hoffman disease. Infants with SMA type II have less severe symptoms during early infancy, but they become progressively weaker with time. SMA type III is the least severe form of the disease.
Rarely, SMA may begin in adulthood. This is usually a milder form of the disease.
A family history of spinal muscular atrophy is a risk factor for all types of the disorder.
Infants with SMA type 1 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.
Often, weakness is first noted in the shoulder muscles and proximal leg muscles. Weakness gets worse over time and will eventually become severe.
Symptoms in an infant:
Symptoms in a child:
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.
Physical therapy is important to prevent contractions of muscles and tendons and abnormal curvature of the spine (scoliosis). Bracing may be necessary.
The lifespan in SMA type 1 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.
Call your health care provider if your child:
Breathing difficulty can rapidly become an emergency condition.
Genetic counseling is recommended for prospective parents with a family history of spinal muscular atrophy.