Spinal muscular atrophy (SMA) is a rare genetic disorder that causes weakness. It affects motor neurons in the spinal cord, resulting in weakness of the muscles used for movement. Signs and symptoms may be present at birth.

If your baby has SMA, it will limit their muscle strength and their ability to move. Your baby may also have difficulty breathing, swallowing, and feeding.

Here, learn about how SMA may affect your child, as well as some of the treatment options that are available to manage this condition.

SMA is classified into five types, based on the age when symptoms appear and the severity of the condition. All types of SMA are progressive, which means they get worse over time.

Type 0

Type 0 SMA is the rarest and most severe type.

When a baby has type 0 SMA, the condition may be detected before they’re born, while they’re still developing in the womb. The baby might not move as expected while growing in the womb.

Babies born with type 0 SMA have extremely weak muscles, including weak respiratory muscles. They often have trouble breathing.

Most infants born with type 0 SMA don’t survive for more than 6 months.

Type 1

Type 1 SMA is also known as Werdnig-Hoffmann disease or infantile-onset SMA. It’s the most common type of SMA, according to the National Institutes of Health (NIH).

When a baby has type 1 SMA, they will likely show signs and symptoms of the condition at birth or within 6 months of being born.

Children with type 1 SMA typically can’t control their head movements, roll over, or sit without help. Your child may also have difficulty sucking or swallowing.

Children with type 1 SMA also tend to have weak respiratory muscles and abnormally shaped chests. This can cause serious breathing difficulties.

Many children with this type of SMA don’t survive past early childhood. However, new targeted therapies may help improve the outlook for children with this condition.

Type 2

Type 2 SMA is also known as Dubowitz disease or intermediate SMA.

If your baby has type 2 SMA, signs and symptoms of the condition will likely appear between the ages of 6 and 18 months.

Children with type 2 SMA typically learn to sit on their own. However, their muscle strength and motor skills tend to decline over time and they lose motor skills that they already had. Eventually, they often need more support to sit.

Children with this type of SMA typically can’t learn to stand or walk without support. They often develop other symptoms or complications as well, such as tremors in their hands, unusual curvature of their spine, and breathing difficulties.

Many children with type 2 SMA usually survive into their 20s or 30s.

Types 3 and 4

In some cases, babies are born with types of SMA that don’t produce noticeable symptoms until later in life.

Type 3 SMA is also known as Kugelberg-Welander disease or mild SMA. It typically appears after 18 months of age.

Type 4 SMA is also called adolescent- or adult-onset SMA. It appears after childhood and tends to cause only mild to moderate symptoms.

Children and adults with type 3 or type 4 SMA may experience difficulties with walking or other movements, but, with treatment and prevention of complications, they can have a typical life expectancy.

SMA is caused by mutations in the SMN1 gene. The type and severity of the condition is also affected by the number and copies of the SMN2 gene that a baby has.

To develop SMA, your baby must have two affected copies of the SMN1 gene. People who inherit one affected copy of the SMN1 gene do not have symptoms of SMA.

The SMN1 and SMN2 genes give instructions to the body for how to produce a type of protein known as the survival motor neuron (SMN) protein. SMN protein is essential to the health of motor neurons, a type of nerve cell that passes signals from the brain and spinal cord to muscles.

If your baby inherits 2 affected copies of the SMN1 gene, they cannot produce SMN proteins properly, and they will have clinical symptoms of SMA. This causes motor neurons in their body to die. As a result, their body can’t properly send motor signals from their spinal cord to their muscles, which leads to muscle weakness, and eventually causes muscle wasting due to lack of use.

If your baby shows signs or symptoms of SMA, their doctor can order genetic testing to check for the genetic mutations that cause the condition. This will help their doctor learn if your child’s symptoms are caused by SMA or another disorder.

In some cases, the genetic mutations that cause this condition are found before symptoms develop. If you or your partner has a family history of SMA, your doctor might recommend genetic testing for your child, even if your child appears healthy. If your child tests positive for the genetic mutations, their doctor may recommend starting immediate treatment for SMA.

In addition to genetic testing, your doctor might order a muscle biopsy to check your child’s muscle for signs of muscle disease. They might also order an electromyogram (EMG), a test that allows them to measure the electrical activity of muscles.

There is currently no known cure for SMA. However, multiple treatments are available to help slow the progression of the disease, relieve symptoms, and manage potential complications.

To provide the support that your baby needs, their doctor should help you assemble a multidisciplinary team of healthcare professionals. Regular checkups with members of this team are essential for managing your child’s condition.

As part of their recommended treatment plan, your child’s health team may recommend one or more of the following:

  • Targeted therapy. To help slow or limit the progression of SMA, your child’s doctor may prescribe and administer the injectable medications nusinersen (Spinraza) or onasemnogene abeparvovec-xioi (Zolgensma). These medications target underlying causes of the disease.
  • Respiratory therapy. To help your baby breathe, their health team may prescribe chest physiotherapy, mechanical ventilation, or other respiratory treatments.
  • Nutritional therapy. To help your baby get the nutrients and calories they need to grow, their doctor or dietitian may recommend nutritional supplements or tube feeding.
  • Muscle and joint therapy. To help stretch their muscles and joints, your child’s health team may prescribe physical therapy exercises. They may also recommend the use of splints, braces, or other devices to support healthy posture and joint positioning.
  • Medications. To treat gastroesophageal reflux, constipation, or other potential complications of SMA, your child’s health team may prescribe one or more medications.

As your child gets older, their treatment needs will likely change. For example, if they have severe spinal or hip deformities, they may need surgery in later childhood or adulthood.

If you’re finding it emotionally difficult to cope with your baby’s condition, let your doctor know. They may recommend counseling or other support services.

Your baby’s physical therapist, occupational therapist, or other members of their health team may encourage you to invest in special equipment to help care for them.

For example, they may recommend:

  • light-weight toys
  • special bath equipment
  • adapted cribs and strollers
  • molded pillows or other seating systems and postural supports

If anyone in your family or your partner’s family has SMA, your doctor may encourage you and your partner to undergo genetic counseling.

If you’re thinking about having a baby, a genetic counselor can help you and your partner assess and understand your chances of having a child with SMA.

If you already have a child with SMA, a genetic counselor can help you assess and understand the chances that you will have another child with this condition.

If you have multiple children and one of them is diagnosed with SMA, it’s possible that their siblings may also carry the affected genes. A sibling might also have the disease but not be showing noticeable symptoms.

If your doctor believes that any of your children are at risk of having SMA, they can order genetic testing. Early diagnosis and treatment may help improve your child’s long-term outlook.

What is the life expectancy of a baby with SMA?

Life expectancy will depend on the type of SMA. Babies with type 1 do not usually survive the first 2 years of life, but those with type 2 may live at least into adolescence. A person with type 3, which usually appears after the age of 18 months, can expect a typical life expectancy.

At what age is SMA diagnosed?

The signs of SMA type 1 are usually apparent before an infant reaches 6 months. Type 2 appears at 6–18 months, and type 3 becomes evident after 18 months. Another type, type 4, does not occur until after the age of 21 years.

If your child has SMA, it’s important to get help from a multidisciplinary team of healthcare professionals. They can help you understand your child’s condition and treatment options.

Depending on your child’s condition, their health team may recommend treatment with a targeted therapy. They may also recommend other treatments or lifestyle modifications to help manage the symptoms and potential complications of SMA.

If you’re finding it difficult to cope with the challenges of caring for a child with SMA, let your doctor know. They can refer you to a counselor, support group, or other sources of support. Having the emotional support that you need can enable you to better care for your family.