SMA Types, Causes, and Treatments

Spinal Muscular Atrophy (SMA) is a hereditary disorder that can cause nerve damage and skeletal muscle dysfunction. This can make common tasks like walking and breathing very difficult. This article describes the symptoms of SMA, its different types, its cause, and some available treatment options.

What is SMA?

Spinal Muscular Atrophy is a blanket name for several neuromuscular disorders that disrupt communications between certain nerves and muscles. Over time, this degrades nerves in the central nervous system (CNS) that regulate functions like swallowing, speaking, walking, and even breathing.

More specifically, SMA causes destruction to lower motor neurons that modulate muscles in the tongue, face, throat, chest, arms, and legs. This can result in muscle weakness, muscle wasting (atrophy), drooling, speech impediments, and involuntary muscle twitching (fasciculations).

Some types of spinal muscular atrophy cause miscommunications between upper motor nerves, which are in the brain, and lower motor neurons, which serve as links between the upper motor neurons and skeletal muscles.

This can cause muscles in the arms and legs to develop progressive stiffness, which doctors refer to as “spasticity.” Over time, this can cause movements to be painful, and resultantly, slow and tedious. In many cases, the tendons in the limbs become overactive, causing involuntary jerks and twitches.

In some cases, SMA causes the individual to lose all voluntary control over limb movement and function. Although there is no known cure for spinal muscular atrophy, those who have it can still live normal life spans.

Types of Spinal Muscular Atrophy

There are 4 main types of SMA, as well as several other types that are less common. The four primary types of this hereditary condition are based on the age when symptoms are first diagnosed and certain physical milestones as follows:

Type I SMA

  1. The most common and most severe form
  2. Normally occurs within the first 6 months of life
  3. Causes weakness; and difficulty breathing, swallowing, and coughing
  4. Also called Werdnig-Hoffmann disease
  5. Often fatal


  1. Typically diagnosed between 6-24 months of age
  2. Causes baby to fail at meeting age-appropriate physical milestones
  3. May be able to stand but cannot walk; often requires a wheelchair


  1. Typically diagnosed after 18 months of age
  2. Can manifest as late as the teenage years
  3. Initially unable to walk
  4. Develop limited mobility with time
  5. Wheelchair assistance is sometimes needed
  6. Also called Juvenile SMA or Kugelberg-Welander disease


  1. Manifests during adulthood and is very rare
  2. Symptoms normally show after age 35
  3. Typically causes mild motor impairment

Causes of SMA

Spinal muscular atrophy is a hereditary disorder. It is caused by a defect in the SMN1 gene, which is responsible for producing a protein chain that helps keep motor neurons alive. Fittingly, it is called the SMN protein.

When the body produces too little of the SMN protein, lower motor neurons can begin to degrade, which then causes some skeletal muscles to become weak, stiff, and atrophied (shrunken).

In most cases, the weakness is noted in the large muscles of the arms and legs, and not so much in the smaller muscles of the hands and feet.

Spinal Muscular Atrophy Treatments

There is no cure for spinal muscular atrophy. However, there are several methods that your doctor may recommend to help manage the symptoms and prevent complications from developing. Some of these include:

  • A prescription drug called Spinraza (nusinersen)
  • Muscle relaxant drugs like tizanidine and baclofen
  • Benzodiazepine drugs like Valium and Xanax to reduce spasticity
  • Amitriptyline, glycopyrrolate, or atropine to reduce drooling
  • Physical therapy or occupational therapy
  • Therapy to improve swallowing and speech
  • Braces, wheelchairs, speech synthesizers, and other assistive devices

As with all health disorders, it is important to maintain a healthy eating plan. The foods we eat are very important for reducing inflammation, pain, limited mobility, and other symptoms linked to SMA.

There are 4 primary types of spinal muscular atrophy, a hereditary disorder that causes damage to lower motor nerves that control breathing, swallowing, walking, and other basic functions.

In some cases, people with SMA stabilize and show few symptoms for long periods of time. However, permanent remission should not be expected for this incurable nervous system disorder. It is important to work closely with your doctor to minimize adverse symptoms and optimize well-being.


NIH – Spinal Muscular Atrophy Fact Sheet
Cure SMA – Types of SMA
MDA – Spinal Muscular Atrophy

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