Spinal muscular

Learn about spinal
muscular atrophy and
what we’re doing to help

What is spinal muscular atrophy?

Spinal muscular atrophy (SMA) is an inherited disease that is caused by damage to certain nerve cells in the brain and spinal cord called motor neurons. This damage gets worse over time, affecting actions like swallowing, breathing, sitting and walking.

What causes SMA?

SMA is a genetic disease that is caused when an abnormal or missing SMN1 gene is passed from both parents to their children.


SMA has several types, based on how severe the symptoms are and at what age they start.

What does a deficient SMN1 gene mean?

This means that the body does not make enough of the survival motor neuron (SMN) protein needed for motor nerve function. This causes the symptoms of SMA mentioned above.

What’s the role of the SMN2 gene?

SMN2 is similar to SMN1 but genetic differences in SMN2 result in SMN protein levels that are insufficient to maintain motor nerve function in the absence of SMN1.

What are the different types of SMA?

Type 0

This type of SMA is very rare and severe. A mother can sense a child is not moving much or not at all while she’s pregnant. After birth, the child is weak with very little muscle tone. Children with type 0 SMA generally survive for less than 6 months due to weak breathing muscles leading to respiratory failure.

Type I

This is also called Werdnig-Hoffmann disease, or infantile SMA. SMA type I is the most common form, usually diagnosed between birth and 6 months of age. Children with type I have decreased muscle tone and struggle to suck, swallow and breathe. They often have trouble sitting unassisted. If not treated, type I can be fatal early on in life.

Type II

This is usually diagnosed before a child is 18 months old. Most children with type II can sit without help but can’t stand or walk and need a wheelchair. They tend to get scoliosis (a curved spine) over time, and may gradually lose the ability to sit and need breathing support. They may survive into adulthood.

Type III

This is also known as Kugelberg-Welander syndrome, and symptoms start after around 18 months of age. Most children with type III can stand and walk without help but walking and climbing stairs can become difficult. They’ll need a wheelchair later in life and breathing support. People with type III tend to have normal life spans.

Type IV

SMA type IV is very rare. Symptoms usually develop after the age of 30. A person may have a tremor, muscle weakness and twitching. People with type IV generally have normal life spans and maintain their mobility.

Our SMA research

We’re looking at several areas of research for people living with SMA, including:

  • The safety and potential side effects of an investigational drug at different doses and over a long period of time
  • What effect a higher dose of an investigational drug may have for people living with SMA
  • If an investigational drug could help prevent or delay respiratory interventions or death in infants who aren’t yet showing symptoms or have been diagnosed with genetic SMA
  • The impact an investigational drug may have on aspects of SMA, such as motor function, in people who have previously received other treatments for SMA

What could a Biogen SMA trial involve?

Before you or your loved one joins a trial, we first confirm your eligibility with some health assessments. Then if you’re eligible and choose to take part in an SMA trial, you’ll need to attend several appointments so that the trial team can closely monitor your health and condition with health assessments, such as:

Lumbar puncture

Lumbar punctures involve inserting a needle between the bones of the spine in the lower back, in order to take a small amount of cerebrospinal fluid (fluid surrounding the brain and spinal cord). The trial doctor will discuss any risks associated with this procedure with you, including, but not limited to: headache and back discomfort/pain.

Examination of the nervous

Depending on you or your child’s age, we would observe movement skills and the senses, as well as balance and coordination, mental status (level of awareness, speech, and language, and ability to interact with the environment), reflexes, and functioning of the nerves. For small children, sense tests can include whether they can feel a pinprick sensation and vibrations, which they may find a little uncomfortable.

Genetic testing

This involves examining a person’s DNA, the chemical database that carries instruction for the body’s functions. Genetic testing can reveal changes (mutations) in genes that may cause illness or disease.

Other assessments will be involved. A full list of these, and all other requirements around taking part in a trial, would be fully discussed with you before you made a decision about whether to join a trial or not.

And remember, if you join a clinical trial, there are many rules and regulations in place to protect your rights, safety, welfare and personal data.

What is the role of a caregiver in an SMA clinical trial?

Parents or guardians will accompany small children who take part in an SMA trial. Visit our section on clinical trials in children for more information about what to expect if your child takes part in a trial. If you’re an adult taking part in an SMA trial, someone who cares for you, for example a partner, sibling, other family member, close friend, or professional caregiver, may help you get to and from your appointments and support you throughout the trial. They might be asked to help monitor any changes in your condition and report them to us. Visit our section on caregivers for more information about this role.

Travel support for people who take part in trials may be available, in terms of coordination and expenses. Depending on the distance traveled, this may include ground transportation, flights, and hotels.

How can I get involved?

To find effective treatments for SMA, we must first test investigational drugs in clinical trials. But in the same way that diseases like SMA can impact people in different ways, how medicine works in the body can also vary for people of different races and ethnicities. That’s why it’s so important that we have diverse representation of all people in our clinical trials.

You can learn more about the importance of diversity in clinical trials, and Biogen’s efforts to make an impact, here.

Recruiting spinal muscular atrophy trials:

Click to view full study details including trial locations.

Help and resources

There are organizations that offer information and support for people living with SMA and their families. Below are some groups where you can find out more about SMA, connect with others, or learn about the latest research. Remember, this list of organization does not imply an endorsement from Biogen or the listed organization