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What is SMA?

Spinal Muscular Atrophy (SMA) is the term for a group of inherited neuromuscular diseases affecting thousands of children and adults all over the world. The disease destroys motor neurons (also called anterior horn cells) of the spinal cord and brain stem. These nerve cells deliver electrical and chemical signals to voluntary muscles, which are used for crawling, walking, head and neck control, swallowing, and even breathing.

Involuntary muscles, hearing, vision, and intelligence are not affected. It has been noted that most children with SMA are very bright, interactive and socially gifted.


1 of 40 people are carriers of the SMA gene

1 in every 6,000 live births is affected

over 25,000 people in the U.S. have SMA

SMA does not discriminate when it comes to sex, age, race or ethnic background

"Autosomal recessive" types 1-3. Both parents must pass on the defective gene in order for their child to inherit the disease

Four Types of SMA:

Type 1 (Werdnig Hoffmann) – Most Severe Form. The onset is before birth or up to 6 months of age. The child will never sit or stand. Respiratory and swallowing problems are their biggest threat. Quivering of the tongue is often noticed. This clinical sign is seen in virtually no other disease in children except for SMA. The survival rate is usually less than 2 years. However, each child is affected differently and a small number of children with Type 1 may survive into their teens or early adulthood. Also, as more is learned about SMA, the lifespan of a Type 1 child can be lengthened depending on the severity of the symptoms for each particular child.

Type 2 - Usually strikes between 9 and 18 months of age. The child can usually sit independently, however, they almost never achieve the ability to walk or stand without support. Depending on severity, many live into adulthood.

Type 3 (Kugelberg-Welander Disease) - Can strike at any time after 18 months of age. Many children can appear normal until 10 or even older. The degree of weakness varies. They are able to walk and have normal life spans.

Type 4 (Adult) – There are many forms of adult onset, differing in age of onset. The degree of weakness varies greatly with each individual.

Please note: Although the preceding classifications of SMA is useful to patient and families, it must be noted that these statistics are not hard-fast rules. The line between each Type of SMA is not clearly defined and there can be an overlapping of types. Additional understanding of the gene defects will undoubtedly explain the tremendous clinical variation that is demonstrated.

Disclaimer: All information contained in this web site is intended for informational purposes only and is not intended to replace and should not be interpreted or relied upon as professional advise. It is strongly recommended that you consult a physician to assess individual conditions and needs.