Spinal muscular atrophy type 2 is less common and less severe than type 1. Symptoms typically begin within 18 months of birth. With treatment and supportive devices, people with the disease often live into their 20s.

Spinal muscular atrophy (SMA) is an inherited neuromuscular disorder that causes progressive muscle weakness. It’s one of the most common recessive genetic disorders, occurring in about 1 in 10,000 live births.

SMA type 2 is a less common form of SMA. Symptoms begin later than in the more common type 1. SMA type 2 is also known as Dubowitz disease or intermediate SMA.

There’s no cure for SMA. But in recent years, early diagnosis and new targeted therapies have shown great promise in preserving motor function and improving the quality of life for many children with SMA and their families.

Babies with SMA type 2 often do not have symptoms at birth. Symptoms first appear at 6–18 months of age.

Children with type 2 SMA can often hold up their heads, roll, and sit by the time symptoms appear. But they go on to develop the following progressive symptoms:

SMA does not affect intelligence.

In many cases, doctors can now diagnose SMA before symptoms begin. Some diagnoses come from prenatal genetic testing and others from state newborn screening blood tests shortly after birth.

Although there is no cure for SMA type 2, recent advances in diagnosis and treatment of SMA have improved motor function and life expectancy for people with the condition.

Early diagnosis of SMA via newborn screening is now common. This can allow for treatment even before symptoms begin. Newer disease-modifying treatments include:

  • Nusinersen (Spinraza): Spinraza stimulates the production of functional survival motor neuron (SMN) protein in the brain and spinal cord (the central nervous system, or CNS). A healthcare professional injects this medication at regular intervals into the fluid surrounding the spinal cord.
  • Risdiplam (Evrysdi): This oral medication helps increase functional SMN protein in the CNS and throughout the body.
  • Onasemnogene abeparvovec (Zolgensma): Zolgensma is a gene replacement therapy that may help children under 2 years of age. A healthcare professional administers it as a one-time intravenous (IV) infusion.

These therapies may help children with SMA type 2 reach or maintain major motor milestones. You can talk with your child’s doctor to find out whether and when these therapies might be right for your child.

Other supportive care options to discuss with your child’s healthcare team may include:

Children with SMA type 2 may reach early milestones, such as sitting, but usually do not walk on their own. They’ll eventually need assistive devices for mobility, such as braces, walkers, or wheelchairs.

Scoliosis is often progressive and may require bracing or surgery. Joint issues may also need treatment.

As time passes and muscle weakness progresses, children with SMA may have difficulty with feeding and breathing.

Although many people with SMA type 2 survive into early adulthood, respiratory complications often limit life expectancy. Recent advances in treatment have been shown to improve motor function, and research into their effects on life expectancy is ongoing.

Resources for support

An SMA type 2 diagnosis can be overwhelming, stressful, and isolating for families, but support is available. You can talk with your child’s doctor about community and expert resources in your area. Discuss and research your nearest multispecialty SMA center or clinic.

These organizations and web resources may also help you learn more and connect with others in the SMA community:

Was this helpful?

SMA is an inherited genetic disorder. Mutations in your survival motor neuron (SMN1) gene cause the condition. This gene encodes for the SMN protein, which is essential for motor neuron health and function.

SMA is an autosomal recessive disorder. This means that in order to develop the condition, you need to receive two copies of the mutated gene — one from each biological parent.

About 1 in 40 people in the United States carry a single mutated copy of the SMN1 gene. These people do not have symptoms, but they can pass the mutated gene on to their children. A child born to two parents who carry the SMN1 gene mutation has a 1 in 4 chance of having SMA.

Another gene, SMN2, produces smaller amounts of the SMN protein. While it can’t fully make up for a mutated SMN1 gene, having more copies of the SMN2 gene can contribute to a later onset of SMA and milder symptoms.

Children with SMA type 2 typically have three copies of the SMN2 gene, while children with the more severe SMA type 1 typically have only two copies.

SMA is a genetic condition. A family history of SMA increases your risk. Talk with your doctor if you have a family history of the disorder, especially if you’re planning a pregnancy. Because carriers have no symptoms, it’s possible to carry the genetic mutation without knowing it.

The genes that cause SMA are more common among white people and Asian people than among people of other ethnicities.

SMA affects people of all sexes equally.

Doctors classify the four types of SMA based on the age of onset and severity of symptoms.

SMA type 1 is the most common form and the most severe. Infants quickly show signs of weakness and difficulties with feeding and breathing, and they have limited life expectancy.

In contrast, children with SMA type 2 have a slightly later onset of symptoms. Because of this, they can reach more motor milestones, such as rolling and sitting. But their weakness will progress. Eventually, they can experience breathing problems, which can shorten their life expectancy.

SMA types 3 and 4 are even less common and have a later onset, milder symptoms, and a typical life expectancy.

Is there a cure for SMA type 2?

There is currently no cure for any form of SMA. But research is ongoing, and new disease-modifying therapies have shown great promise.

Is SMA type 2 fatal?

SMA type 2 is not fatal in the short term but can affect life expectancy. Breathing problems are the most common life threatening complication of SMA type 2.

What is the life expectancy for people with SMA type 2?

Many people with SMA type 2 survive into adulthood. About 70% of people survive at least into their mid-20s.

Newer disease-modifying therapies may improve both quality of life and life expectancy for people with SMA.

SMA is an inherited motor neuron disease caused by a mutation of the SMN1 gene. SMA type 2 has a milder course and a slightly later onset of symptoms than type 1.

Children born with SMA type 2 begin developing progressive weakness at 6–18 months of age. Weakness tends to affect the legs first, and children with SMA type 2 may not walk on their own. Eventually, weakness progresses, affecting abilities such as feeding and breathing.

A multidisciplinary team of expert SMA professionals can help your family navigate your care plan. While there’s no cure for SMA, emerging therapies may improve quality of life, motor function, and life expectancy in children with this condition.