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.  

An international consortium, co-led by Richard Finkel, MD, found that babies with SMA may benefit from taking the drug risdiplam soon after birth. Read the news release. Scientists at St. Jude also led research exploring whether prenatal risdiplam may improve survival and motor function in infants. Read the news release. 

Learn more

Resources outside St. Jude