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SMN2 gene

Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

SMN2 gene

The SMN2 gene produces the survival motor neuron protein, which is essential for the maintenance of motor neurons and helps modify the severity of spinal muscular atrophy.

Normal Function

The SMN2 gene provides instructions for making the survival motor neuron (SMN) protein. The SMN protein is found throughout the body, with highest levels in the spinal cord. This protein is one of a group of proteins called the SMN complex, which is important for the maintenance of specialized nerve cells called motor neurons.

Several different versions of the SMN protein are produced from the SMN2 gene, but only one version (called isoform d) is full size and functional. The full-size protein made from the SMN2 gene is identical to the protein made from a similar gene called SMN1; however, only 10 to 15 percent of all functional SMN protein is produced from the SMN2 gene. The number of copies of the SMN2 gene varies among individuals; the more SMN2 gene copies a person has, the more SMN protein they produce.

In cells, the SMN complex plays an important role in processing molecules called messenger RNA (mRNA). The SMN complex is also important for the development of specialized outgrowths from nerve cells called dendrites and axons, which are required for the transmission of impulses between neurons and from neurons to muscles.

Health Conditions Related to Genetic Changes

Spinal muscular atrophy

Extra copies of the SMN2 gene do not cause spinal muscular atrophy, but they modify the severity of the disorder. This condition is characterized by a loss of motor neurons that leads to weakness and wasting (atrophy) in muscles used for movement that worsens with age.

All individuals with spinal muscular atrophy have mutations in both copies of the SMN1 gene. As a result, little or no SMN protein is produced from this gene. The SMN2 gene can help replace some of the missing SMN protein. In people with spinal muscular atrophy, having multiple copies of the SMN2 gene is usually associated with less severe features of the condition that develop later in life.

  • Affected individuals with one or two functional copies of the SMN2 gene generally have severe muscle weakness that begins at birth or in infancy.
  • Affected individuals with four or more copies of the SMN2 gene typically have mild muscle weakness that may not become noticeable until adulthood.

Other Names for This Gene

  • BCD541
  • C-BCD541
  • centromeric SMN
  • SMN_HUMAN
  • SMNC

Frequently Asked Questions

While the SMN2 gene does not cause spinal muscular atrophy (SMA), it significantly modifies its severity. The SMN2 gene produces some functional survival motor neuron (SMN) protein, though less efficiently than the SMN1 gene. Individuals with more copies of the SMN2 gene can produce more functional SMN protein, which can help compensate for the SMN1 gene defect and lead to a milder form of SMA.
Knowing the number of SMN2 gene copies is crucial for individuals with SMA because it is a key prognostic indicator. A higher number of SMN2 copies generally correlates with a milder disease course and better motor function. This information also helps guide treatment decisions, as some therapies aim to increase SMN protein production from the SMN2 gene.
The SMN1 gene is the primary producer of full-size, functional SMN protein. The SMN2 gene is very similar but has a slight difference that causes it to primarily produce a shorter, non-functional version of the protein. However, a small percentage (10-15%) of the SMN2 gene's output is full-size and functional, making it a critical "backup" gene that can partially compensate for a non-functional SMN1 gene.
Yes, several treatments for spinal muscular atrophy (SMA) specifically target the SMN2 gene. These therapies work by modifying the SMN2 gene's splicing process to increase the production of full-length, functional SMN protein, thereby improving motor neuron survival and function in individuals with SMA.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.