Spinal Muscular Atrophy (SMA)

What is Spinal Muscular Atrophy (SMA)?

Spinal Muscular Atrophy (SMA) is an inherited neurological disorder that causes progressive muscle degeneration and weakness. It is caused by a mutation or deletion of the survival motor neuron 1 gene (SMN1). It is one of the leading genetic causes of infant mortality. SMA can affect children during any stage of development, from infancy to adulthood.

Types of Spinal Muscular Atrophy

There are four types of SMA that range from most to less severe:

  • Type I (Werdnig-Hoffman Syndrome) – This is the most severe form of SMA. It typically appears in infants under the age of six months and is characterized by significant muscle weakness that leads to retarded growth and motor development.
  • Type II (Intermediate form) – This is the second most severe form of SMA. This type is often diagnosed during early childhood, typically between ages of 6 months and 3 years. Those affected may develop the ability to sit independently, but will not be able to stand or walk independently.
  • Type III (Kugelberg-Welander Disease) – This type of SMA affects youths and young adults. Symptoms typically begin during childhood, but are often not seen until early adulthood. Those affected typically learn to walk and are then able to walk independently until adulthood.
  • Type IV (adult-onset) – This is the mildest form of SMA and usually presents itself in adults over the age of 35. Symptoms are not as severe as with the other types of SMA and may appear as mild muscle weakness or fatigue.

Diagnosis and Treatment

SMA is a genetic disorder and is usually diagnosed either through genetic testing or through magnetic resonance imaging (MRI). Treatment for SMA varies depending on the type and severity. Treatment may include physical therapy, medications, and assistive devices. SMA is incurable.


Spinal Muscular Atrophy is a genetic disorder that affects the muscles of the body, leading to progressive muscle weakness. There are four types of SMA, ranging from most to least severe, and treatment is based on the type and severity. Though there is no cure, treatments such as physical therapy, medications, and assistive devices can help improve the quality of life for those affected by SMA.