Spinal muscular atrophy

Alternative names:

Werdnig-Hoffmann disease

Definition:

A group of inherited diseases that result in progressive muscle degeneration and weakness.

Causes, incidence, and risk factors:

Spinal muscular atrophy is the second leading cause of neuromuscular disease. (Duchenne muscular dystrophy is number one.) Spinal muscular atrophy is inherited as an autosomal recessive trait and has an incidence of approximately 3 out of 4 per 100,000 people.

In its most severe form (SMA I), infants are born floppy with weak, thin muscles, and feeding and breathing problems. Their lifespan seldom exceeds more than 2 to 3 years. Infants with SMA type II have less severe symptoms during early infancy but they become progressively weaker with time. Survival time with type II is longer. SMA type III is the mildest form of the disease and symptoms may not appear until the second year of life. Often, weakness is first noted in the shoulder muscles and proximal leg muscles. Weakness is progressive and will eventually become profound, but children may survive into early adulthood.