INTRODUCTION
Spinal muscular atrophy (SMA) is a group of inherited diseases that damages the nerves controlling voluntary muscle movement. SMA can affect anyone of any age, race or gender. Approximately one in 6,000 babies is born with SMA. Of children diagnosed before age two, 50 percent will die before their second birthday. One in every 40 people carries the gene that causes SMA. The child of two carriers has a one in four chance of developing SMA.
SMA is classified into several types:
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- Type I (sometimes called Werdnig-Hoffmann Disease), is the most severe form of SMA. Children with Type I tend to be weak and lack motor development. They cannoot sit unaided and have trouble breathing, sucking and swallowing. Type I SMA is usually manifested in infants between birth and six months.
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- Type II is slightly less severe. Type II patients may be able to sit unaided or even stand with support and usually do not suffer from feeding and swallowing difficulties. However, they are at increased risk for complications from respiratory infections. Type II SMA affects infants between seven and 18 months old.
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- Type III,also known as Kugelberg-Welander Disease, is the least deadly form of childhood-onset SMA. Type III patients are able to stand, but weakness is prevalent and tends to eventually sentence its victims to a wheelchair. Type III SMA strikes children after the age of 18 months, but can surface even in adulthood.
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- Type IVis the adult form of the disease in which symptoms tend to begin after age 35. Symptoms usually begin in the hands, feet and tongue, and spread to other areas of the body.
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