Spinal Muscular Atrophy

SMA happens when there’s a problem with a gene that helps your child’s body maintain motor neurons.

Most types of SMA happen because a gene called survival motor neuron 1 (SMN1) is missing or abnormal.

• Healthy SMN1 makes survival motor neuron (SMN) protein.
• Abnormal SMN1 makes much less SMN protein or none at all.

Without enough SMN protein, motor neurons shrink and eventually die.

A “back-up” gene, SMN2, produces some SMN protein. It can partly make up for faulty SMN1. Some people have more copies of the SMN2 gene than other people do. Typically, the more SMN2 copies your child has, the later their symptoms will start and the milder their symptoms will be.

Changes to other genes besides SMN1 can cause other types of SMA.

Children with SMA are born with an abnormal gene that affects their motor neurons. In some babies, it’s clear they have SMA right after birth. But it may take months or years before a child shows any signs or symptoms that family members or doctors would notice. Some people with mild SMA have no symptoms until adulthood.

Doctors group SMN-related SMA into types based on your child’s highest level of abilities and number of SMN2 copies.

Type 1 SMA:

• Your baby cannot control their head movement well and cannot sit or stand on their own.
• Usually diagnosed by the age of 6 months.
• Also called Werdnig-Hoffman disease or infantile-onset SMA.

Type 2 SMA:

• Your child can sit on their own but may need help getting into a seated position. They may be able to stand with help but cannot walk.
• Usually diagnosed by age 2.
• Also called intermediate SMA.

Type 3 SMA:

• Your child can stand and walk on their own, but they may have trouble walking, running or climbing stairs as they get older.
• Usually diagnosed by age 3 but sometimes as late as the teen years.
• Also called Kugelberg-Welander disease or juvenile SMA.

Type 4 SMA:

• Your young adult may have mild motor problems, like muscle weakness, tremors (fine shaking) and twitching.
• Usually diagnosed after age 35 but sometimes as early as 18.
• Also called adult-onset SMA.

You will find more details about types 1 to 4 in the section about symptoms.

Other, less common types of SMA include:

• Spinal muscular atrophy respiratory distress (SMARD), which affects babies and causes serious breathing problems
• Distal SMA, which mainly affects the hands and feet

Each child with SMA is unique. One thing they all have in common is some degree of muscle weakness.

The age when symptoms start and the effects on motor function can vary widely. Typically, function gets worse over time because the child’s muscles cannot keep up with their growth. But your child may have long periods where their physical abilities are stable.

SMA does not affect your child’s:

• Brain, intelligence or ability to think and learn
• Emotions or ability to have relationships with family and friends
• Sensory nerves or ability to feel touch or pain

In 2016, the U.S. Food and Drug Administration approved the first medicine to treat SMA. Nusinersen (Spinraza) slows weakness and even improves strength in some people with SMA by improving the ability of the SMN2 gene to make more complete SMN protein.

There is no cure yet for the disease, but together you and your child’s healthcare team can support your child’s movement, strength, comfort and health so they have a rich, active life at home, at school and in the community.

The lifespan for children with SMA can vary widely. Most children with type 1 SMA who do not get treatment live less than 2 years. Advances in lung support along with nusinersen have greatly improved their lifespan. Most children with type 2 live into young adulthood or longer. Those with type 3 or 4 usually have a normal lifespan.

Children are born with SMN-related SMA if both of their parents passed them an abnormal gene that causes the disease.

Each parent can have 1 normal gene and 1 abnormal gene, making them carriers. They do not have SMA, and typically they do not have any idea they carry the abnormal gene. This is fairly common; somewhere between 1 in 40 and 1 in 90 people are SMA carriers.

If a child inherits 2 abnormal genes – 1 from each parent – the child will have SMN-related SMA.

Other, less common types of SMA can happen when only 1 parent passes an abnormal gene to their child.

• We have been named an SMA Care Center by CureSMA and an MDA Care Center by the Muscular Dystrophy Association. Both are leading advocacy groups for people with SMA.
• Our dedicated team – doctors, nurse practitioners, therapists, dietitians, genetic counselors and social workers – has expertise and experience in diagnosing and treating SMA.
• Seattle Children’s brings together pediatric specialists from Rehabilitation Medicine, Neurology and Pulmonary and Sleep Medicine to evaluate your child’s unique needs.
• If your newborn is critically ill due to spinal muscular atrophy, we provide specialized care in our Neuro NICU – the only neonatal neurocritical care program in Washington, Wyoming, Alaska, Montana and Idaho.

• We design and provide care to help your child and family manage SMA and to give your child the best possible function and quality of life, now and as they grow.
• Seattle Children’s provides a full range of treatments, from medicines, therapy and equipment, to respiratory support and orthopedic surgery.

• To make sure your child has a full evaluation and receives complete, coordinated care, we will involve experts from across Seattle Children’s.
• Your child may see their entire team in 1 room on a single day, making the process easier on you and your child.
• Based on your child’s needs, your team may include experts from Orthopedics, Speech and Language Services and other specialties and programs.

Babies with type 1 SMA have these signs and symptoms:

• Overall weakness, which may make them seem floppy
• Poor control of head movement
• Trouble reaching out for toys or lifting their legs in the air
• Cannot sit or stand on their own
• Trouble feeding or swallowing (choking, gagging or inhaling food or liquid into their lungs)
• Small chest, trouble breathing and breathing from their stomach rather than their chest
• Weak cry

As your child’s muscles become weaker, they may not be able to breathe well enough on their own and may need equipment to help. Over time, your baby may start having other health issues linked with muscle weakness, such as scoliosis or kyphosis, hipbones that don’t stay well in their sockets (hip displacement) and weak bones that break easily.

Children with type 2 SMA have these signs and symptoms, usually by age 2:

• Delays in reaching typical motor milestones (like holding up their head, rolling over, crawling and sitting)
• Can sit on their own but may need help getting into a seated position
• May be able to stand and take some steps with help
• Cannot walk on their own
• May have trouble getting enough food by mouth to support typical growth
• May have trouble breathing or coughing when they need to clear their airway

As your child gets weaker, they may need help to breathe during sleep or to sit on their own. Over time, your child may get scoliosis, kyphosis, hip displacement, weak bones that break easily or other health issues linked with muscle weakness.

Children with type 3 SMA can sit, stand and walk on their own.

They may start to show these signs and symptoms as they get older – usually by age 3 but sometimes not until later in childhood or as a teen:

• Trouble walking, running or climbing stairs
• Falling often
• Tremors in their hands and fingers
• Joint aches

Over time, your child may start having other issues with their health or function related to weaker muscles, such as:

• Trouble swallowing, coughing or breathing during sleep
• Weight gain from not being able to be as active
• Scoliosis or kyphosis
• Hip displacement
• Weak bones that break easily

As your child’s muscles become weaker, they may lose their ability to walk.

People with type 4 SMA don’t show signs and symptoms until later in life, usually after age 35 but sometimes as early as 18. As a young adult with type 4 SMA, your child may start having:

• Weakness that comes on slowly
• Tremors or twitching
• Breathing trouble

The Neuromuscular Program team includes experts from Rehabilitation Medicine, Neurology, Pulmonary and Sleep Medicine, Endocrinology and the Heart Center, as well as dietitians, genetic counselors and social workers.

Based on your child’s needs, we also involve specialists from other clinics and programs around Seattle Children’s, such as:

• Speech and Language Services if your child has trouble feeding or swallowing, which may put your child at risk of not getting the nutrition they need or of getting food or liquid in their airways (aspirating)
• Orthopedics if surgery might help your child with conditions like scoliosis or kyphosis

Common treatments to support your child’s ability to move and do the things they want to do include:

• Physical therapy to maintain range of motion and flexibility and to evaluate whether your child needs equipment
• Occupational therapy to help your child with activities like dressing and using a computer keyboard
• Braces for your child’s legs to help them stand and move on their own, for their wrists or hands to provide support or for their back to keep a spinal curve from getting worse
• Devices that help your child sit up, stand, walk or get around, such as a seating system, walker, standing frame, wheelchair or motorized scooter
• Nusinersen (Spinraza), a medicine put into the cerebrospinal fluid (CSF) through a needle in your child’s low back to slow their muscle weakness and maybe improve their strength
• Surgery to treat severe scoliosis or kyphosis so your child can sit up or sleep more comfortably or breathe more easily

We will evaluate how well your child’s lungs work as their breathing muscles become weaker, with a focus on preventing and treating respiratory infections.

Infections can become serious if weak breathing muscles make it hard for your child to cough out phlegm. A device called a cough-assist machine can help your child get a deeper breath and then clear their airways. A respiratory therapist sets up the machine and teaches you how to use it.

Some children with SMA may need a machine to help with breathing (bilevel positive airway pressure [Bi-PAP]). Some children start by using Bi-PAP only at night and gradually need to use it more of the time.

A dietitian and others on your child’s team will work with you and your child to:

• Make sure your child gets the nutrition they need for the best growth and development, including brain development
• Get the right amount of calories to keep your child from becoming overweight if they are less able to be active over time
• Adjust your child’s diet, if needed, when they have a respiratory illness or other condition that affects the nutrition they need
• Think about starting tube feeding (such as with a gastrostomy tube or nasogastric tube) if your child cannot chew and swallow safely and learn how to use a feeding tube at home

A social worker focuses on supporting your child and family and helps with coping, social relationships, behavior and emotions. Along with your child’s doctors, nurses and therapists, the social worker will connect you with helpful resources at Seattle Children’s and in the community.