Spinal Muscular Atrophy (SMA)

What is spinal muscular atrophy?

Spinal muscular atrophy (SMA) is a rare genetic condition in which muscles throughout the body are weakened because cells in the spinal cord and brainstem do not work properly. SMA is the number one genetic cause of infant mortality.

There are three types of SMA:

  • Type I is the most severe form of SMA. It’s sometimes called Werdnig-Hoffmann disease. Children with type I have limited movement, can’t sit without support, and have trouble breathing, feeding and swallowing. Symptoms begin within months after birth. Many children with type I do not live past age 2.
  • Type II is an intermediate form of SMA. Children with this type may sit without support at some point but cannot walk on their own. Symptoms typically start between 6 and 18 months of age. Depending on the severity of symptoms, children with type II may have a normal life span. 
  • Type III is a milder form of SMA. It’s also known as Kugelberg-Welander disease and resembles muscular dystrophy. While children with type III usually are able to walk, most have some difficulty walking. Some may eventually need to use a wheelchair. Symptoms usually appear around 18 months of age or in early childhood. Children with this type of SMA generally have an almost normal life expectancy. 

New SMA treatments offer hope

Two new  treatments for SMA — a gene therapy for SMA type 1 and a drug for both children and adults with SMA — are showing promising results. The gene replacement therapy that goes by the brand name Zolgensma (previously AVXS-101) is a one-time infusion that delivers a functional copy of the defective or missing gene to affected cells. Nusinersen (brand name Spinraza) is a medication injected into the spinal fluid that increases the body’s ability to produce a protein called survival motor neuron (SMN).

Before these options became available, treatment of SMA consisted of managing the symptoms, providing respiratory support as needed and preventing disease complications.

How we care for spinal muscular atrophy

The Spinal Muscular Atrophy Program at Boston Children’s Hospital brings together a team of experts from different specialties experienced in caring for children with SMA. We hold a dedicated SMA clinic once a month so that your child can receive all of their SMA-related care in a single visit. This approach means that our various specialists can all work closely with your family to make sure your child’s care is well coordinated.

Our program offers gene therapy and nusinersen for treatment of SMA.