Understanding SMA

Spinal Muscular Atrophy (SMA) is a genetic disease that affects nerve cells in the spinal cord that control muscles, as well as other cells throughout the body.1 SMA can affect any race or gender.1

The Cause of SMA

SMA begins with a mutation in the survival of motor neuron 1 (SMN1) gene, which leads to a deficiency of SMN protein. This protein is found throughout the body and is essential to the function of nerves that control muscles as well as other tissues in the body. Without it, nerve cells cannot function correctly, leading to muscle weakness that can sometimes be fatal.1

SMA impacts basic vital functions, including a person's ability to1:


The Role of SMN2

People with SMA also have a “back-up” gene called the survival of motor neuron 2 (SMN2) gene that is nearly identical to SMN1. SMN2 also makes SMN protein but with much less efficiency.2 The severity of SMA is related to the number of SMN2 gene copies a person has, and the amount of SMN protein a person can make.3

SMN1 gene:

Functional SMN protein

SMN2 gene:

80-95% non-functional SMN protein4

SMA by the Numbers

SMA is the leading genetic cause of death in infants and toddlers.2

~1 In


infants are affected by SMA.5
People affected in the U.S.:

Types and Symptoms of SMA

There are four primary types of SMA: I, II, III and IV. The type of SMA is determined by the number of SMN2 genes, the age when symptoms begin and physical milestones reached. SMA type I is characterized by the most severe symptoms and type IV, mild symptoms.5

Even individuals with the same type of SMA will have varied experiences or disease progression.6

Type I

2 copies of SMN27
Typically Diagnosed

0 - 6 months6


Cannot sit independently.7 60% of all SMA cases and usually fatal by age two.6,2

Type II

3 copies of SMN27
Typically Diagnosed

6 months - 2 years6


Often experience respiratory issues and are unable to walk.7

Type III

3-4 copies of SMN27
Typically Diagnosed

18 months - teens6


Can learn to stand and walk, but may lose this ability in the future.6

Type IV

3-4 copies of SMN27
Typically Diagnosed

Usually after age 356


Rare type with slower progression of symptoms, affects walking.6

Living with SMA

Because the majority of people with SMA have different physical abilities, there are resources available to help manage the disease through physical and occupational therapy, nutrition and home modifications.8 Learn more here: https://www.curesma.org/local-support/.

Scientists around the world are researching new potential treatment options for people living with SMA.9