Spinal Muscular Atrophy

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What is spinal muscular atrophy?

Spinal muscular atrophy (SMA) is a group of inherited genetic muscle-wasting disorders. SMA affects the nerve cells that control voluntary muscle. These nerve cells are called motor neurons, and SMA causes them to die off.

Types of SMA

People with SMA are generally grouped into one of four types (I, II, III, IV) based on their highest level of motor function or ability.

  • Type I (severe) – also known as infantile-onset or Werdnig-Hoffman disease
  • Type II (intermediate)
  • Type III (mild) – also known as Kugelberg-Welander disease
  • Type IV – also known as adult SMA

How common is SMA?

SMA is rare condition, occurring in approximately 1 out of every 6,000 live births. It is a autosomal recessive genetic disease. About 1 out of 40 people are genetic carriers of the disease (meaning that they carry the mutated gene but do not have SMA).

What causes SMA?

SMA is caused by a missing or abnormal (mutated) gene known as survival motor neuron gene 1 (SMN1). In a healthy person, this gene produces a protein in the body called survival motor neuron (SMN) protein. In a person with mutated genes, this protein is absent or significantly decreased, and causes severe problems for motor neurons. Motor neurons are nerve cells in the spinal cord which send out nerve fibers to muscles throughout the body. Since SMN protein is critical to the survival and health of motor neurons, nerve cells may shrink and eventually die without this protein, resulting in muscle weakness.


Fact Sheet on Spinal Muscular Atrophy


Learn about clinical research


Consensus Statement for Standard of Care in Spinal Muscular Atrophy

Journal of Child Neurology, August 2007

Introduction to the Family Guide to the Consensus Statement for Standard of Care

This Family Guide to the Consensus Statement for Standard of Care in Spinal Muscular Atrophy was prepared by SMA Advocates for families affected by SMA. The full text of the Consensus Statement (22 pages) was published in the August 2007 issue of the Journal of Child Neurology.
Printable PDF of Family Guide (no photos)



11 Minutes / 11 Muscles
Video Presentation

Presenter: Jeff Sparks, National Director, Special Projects
Description: A successful professional and community leader, Jeff talks about his life with SMA.
Length: 11:23

Useful Links

Cure SMA

Provides information on a wide array of SMA-related topics, including:

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