Spinal muscular atrophy (SMA) in children

What does spinal muscular atrophy (SMA) in children mean?

When a child has SMA, it means specialized cells in their spinal cord don’t work correctly. They don’t have enough of a protein called survival motor neuron (SMN).

SMN enables nerves in the spinal cord (motor neurons) to help control muscle movement. Without enough SMN, the motor neuron cells die, causing muscles to become extremely weak. This condition can affect a child’s ability to crawl, walk, breathe and swallow. Children with SMA have poor muscle tone and muscle weakness.

Risk factors

In the U.S., about 1 in 11,000 children are born with this condition. About 1 in 40 to 60 people are carriers who could pass it on to their children.

What are the different types of spinal muscular atrophy (SMA) in children?

SMA can vary widely in terms of the age when it starts, the symptoms children have and how quickly the disease progresses. The earlier SMA starts, the more it affects muscle movement.

It is usually divided into four types:

• Spinal muscular atrophy type I - This is the most common and the most severe type of SMA. It usually shows up in the first few months of life with low muscle tone and decreased movements. Babies will have trouble breathing and swallowing.

• Spinal muscular atrophy type II - This type of SMA usually appears when a child is between six and 18 months old. Babies can sit but usually can’t walk or stand without help.

• Spinal muscular atrophy type III - This type of SMA starts after 18 months of age. Children start to develop fatigue, several falls a day, abnormalities walking and may start to walk on their toes. Over time, they usually need help walking.

• Spinal muscular atrophy type IV - This type of SMA, which is very rare, appears in adulthood and typically has milder symptoms than SMA that starts early in life.

What are the signs and symptoms of spinal muscular atrophy (SMA) in children?

• Difficulty swallowing, breathing or holding up the head

• Tremor in the tongue

• Difficulty sitting, standing or walking

• Fatigue that progresses to trouble walking

• Walking on toes

• Curvature of the spine

How is spinal muscular atrophy (SMA) in children diagnosed?

Usually a child is brought to the doctor because they are showing early signs or symptoms of SMA, such as having trouble breathing, sitting or standing, holding their head up and decreased movement of the legs and arms.

Neurology evaluation - If we suspect SMA, we will confirm the diagnosis with a free blood test. If a child tests positive, we will also test the parents or siblings to see if they have the condition or are carrying it in their genes. Most states screen all newborns for SMA at birth.

What causes spinal muscular atrophy (SMA) in children?

This condition can be spontaneous or inherited, which means it’s passed from parent to child in their genes. Sometimes genes go through changes (mutations) that affect how they work. A child will have SMA if both parents have the same mutation. If only one parent has the mutation, the child will not have the condition, but could pass it on to their own children. That is called being a carrier.

How is spinal muscular atrophy (SMA) in children treated?

We typically treat spinal muscular atrophy with therapies that help the body produce more of the SMN protein. Having more SMN protein can slow the development of symptoms, helping a child walk, sit or swallow more easily – especially if treatment is started very early.

Some therapies are given through a spinal tap. Others are a liquid that is swallowed or injected. Your child’s treatment will depend on their age and the stage of the condition. Children’s Health is also involved in research to create new treatments for this condition and help children with SMA live longer, healthier lives.

In addition to medication, your child will have access to a care team that works closely together to care for every aspect of their health, including:

• Neurologists who specialize in nerve and muscle conditions

• Cardiologists who treat the heart

• Pulmonologists who treat the lungs

• Nutritionists who help ensure kids get the right nutrients in their diet

• Physical and occupational therapists to help kids stretch their muscles and move more easily

• Nurses who specialize in neurology disorders

• Social workers and case managers who help manage each child’s overall care

Research

• Phase 2 active treatment study to evaluate the efficacy and safety of SRK-015 in patients with later-onset spinal muscular atrophy

• Phase 3, double-blind, placebo-controlled trial to evaluate the efficacy and safety of apitegromab (SRK-015) in patients with later-onset spinal muscular atrophy receiving background nusinersen or Risdiplam® therapy