FAQs about types of SMA

Category: Types of SMA

Spinal muscular atrophy (SMA) is usually divided into five main types — 0, 1, 2, 3, and 4 — based on the age at symptom onset. All of these types are caused by mutations in the SMN1 gene. There also are several rarer forms of SMA-like disease that are caused by mutations in other genes.

Category: Types of SMA

Figuring out what type of spinal muscular atrophy (SMA) someone has is done by combining clinical observations of a patient’s symptoms and age at onset, with genetic testing that identifies disease-causing mutations. For people with one of the five main SMA types, testing of SMN2 copy number also can help determine the disease type.

Category: Types of SMA

The most common form of spinal muscular atrophy (SMA) is type 1 disease, which accounts for about 60% of cases. SMA type 1 symptoms usually are apparent at birth or develop within an infant’s first 6 months.

Category: Types of SMA

Type 0 spinal muscular atrophy (SMA), also known as prenatal SMA, is generally considered to be the most severe form of the disease. This form is characterized by severe muscle weakness and breathing difficulties that develop while a fetus is still in the womb and are present from birth.

Category: Types of SMA

Adult-onset or type 4 spinal muscular atrophy (SMA) is typically considered the mildest form of the disease. In this type of SMA, symptoms do not usually manifest until after age 35, lifespan is unaffected, and most patients do not fully lose the ability to walk.