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Spinal Muscular Atrophy (SMA)

Spinal muscular atrophy (SMA) is a genetic condition that leads to muscle weakness that gets worse over time. SMA is caused by a loss of nerve cells called motor neurons. These special nerve cells control muscles. The nerve cells are found in the spinal cord and part of the brain.

SMA affects the muscles that help a person speak, breathe, and swallow. It also affects muscles that help perform daily activities, such as walking. When these muscles do not get signals from the nerve cells, they begin to waste away. This is called muscle atrophy.

SMA affects 1 out of every 8,000 to 10,000 people. It can appear at any stage of life, but it is more common in infants and children. About 1 in 40 people carry the gene that causes SMA.

Spinal muscular atrophy causes

Genetic diseases are caused by changes in a person’s DNA, or genetic code. SMA is caused by a change in a small part of the DNA called the SMN1 gene. This gene tells the body to make the survival motor neuron (SMN) protein. The SMN protein is crucial for normal motor neuron function and survival. A gene change that causes the gene to not work properly is called a mutation.

People with the classic form of SMA have 2 missing or mutated copies of the SMN1 gene. This causes the nerve cells that control muscle movement to not function. Over time, these nerve cells die. Their death leads to muscle atrophy. Mutations in a similar gene called SMN2 provide a small amount of the SMN protein, which can affect how severe the disease is.

In most SMA cases, both parents pass on the genetic mutations. This means both parents carry a mutated gene, but they do not have any SMA symptoms. A genetic test can show whether someone carries 1 mutated copy of SMN1. It helps show if a person has a risk of having a child with SMA.

To learn more about SMA and current treatments, visit organizations dedicated to SMA and rare diseases.

Spinal muscular atrophy at St. Jude

St. Jude Children’s Research Hospital is working to deepen the understanding of rare, catastrophic genetic neurological disorders in children. Our aim is to transform the treatment landscape for these disorders. The Center for Experimental Neurotherapeutics (CENT) was established at St. Jude as part of the Pediatric Transitional Neuroscience Initiative (PTNI) to focus on these neurological disorders.

Select children with SMA who are accepted at St. Jude take part in clinical research or clinical trials. The aim of these studies is to help scientists learn more about the disorders and to develop potential treatments.  

Clinical research for spinal muscular atrophy

GENETX: Assessing Gene Therapy Communication Needs

Study goal:

To learn more about participants beliefs, attitudes, and questions about gene therapy to help make web-based resources to share information. This could help patients make treatment decisions.


18 to 35 years old with rare genetic diseases

Published results
G4K: Genomes for Kids

Study goal:

The main goal of this study is to learn more about the reasons childhood tumors form and how to treat them better.

TBANK: Collecting, Banking, and Distributing Human Tissue Samples in St. Jude Biorepository

Study goal:

To provide a high-quality repository of tumor and normal samples to facilitate translational research performed by St Jude faculty and their collaborators

PG4KDS: Clinical Implementation of Pharmacogenetics

Study goal:

1) Test each patient for hundreds of gene variations that might be important for drug use. All of the gene test results will be in the research laboratory, but as time goes on, the study will evaluate scientific evidence and selectively move test results for a few genes into the medical record if the evidence strongly shows that the result can help in better prescribing of drugs for patients; 2) Estimate how often pharmacogenetic test results are moved from research tests into a patient’s medical record; 3) Use methods to choose which of these tests should be put in the medical record; 4) Use computer-based tools in the electronic medical record to help doctors use gene test results when prescribing drugs; 5) Share feelings and concerns of patients and their families about gene test information being put in their medical record.

SJFAMILY: Study of Cancer in Families

Study goal:

The main purpose of this trial is to learn about the genetic causes of cancer. 


Younger than 50 years old

A statue of children running and holding hands

Seeking treatment at St. Jude

Patients accepted to St. Jude must have a disease we treat and must be referred by a physician or other qualified medical professional. We accept most patients based on their ability to enroll in an open clinical trial.

How to seek treatment

Contact the Physician / Patient Referral Office

Call: 1-888-226-4343 (toll-free) or 901-595-4055 (local)  | Fax: 901-595-4011 | Email: | 24-hour pager: 1-800-349-4334


Learn more

Resources outside St. Jude