Spinal Muscular Atrophy

hereditary disease that progressively destroys motor neurons

aadc dopamine deficiency
10000 +

Pediatric Cases
In America

6 mo.

Type 1
Life Expectancy

0 yrs.

Type 2
Life Expectancy

+ 60 %

Type 3 & 4
Survival Probability

Inherited Neuromuscular Disorders

Spinal Muscular Atrophy (SMA)

(SMA) is a group of inherited neuromuscular disorders characterized by loss of nerve cells in the spinal cord called lower motor neurons or anterior horn cells. It occurs in children, typically in the first years of their lives, and is reported to affect an estimated. 1 out of every 10,000 babies worldwide.

There are five types of (SMA) 0-4; categorized by the age of symptom onset and the affect on motor function, with the lowest representing a younger age and more severe case.

Depending on the type of SMA prognosis can vary. Type 1 is the most severe and typically fatal, patients with type 2-3 SMA can often live full live, whereas type 4 is also extremely rare, however it does not cause in any life changing symptoms.

The five types of Spinal Muscular Atrophy SMA are:

  • Type 0 – occurs prenatally and is extremely rare. It causes a decrease in fetal movement during pregnancy. Patients with SMA type 0 typically present with severe weakness and hypotonia at birth.
  • Type 1 – is the most common and severe form of SMA; often cuasing death before the 2nd birthday. It’s sometimes called Werdnig-Hoffmann disease or infantile-onset SMA.
  • Type 2 – is an intermediate form of SMA. Children with this type may sit without support at some point but cannot walk on their own. 
  • Type 3 – is a milder form of SMA. It’s also known as Kugelberg-Welander disease and resembles muscular dystrophy. 
  • Type 4 – is very rare. It usually starts in young adulthood and causes mild motor impairment.

Related Conditions

Other medical conditions also associated with SMA include:

spinal muscular atrophy
Spinal Muscular Atrophy Symptoms

Spinal Muscular Atrophy (SMA) Symptoms

The symptoms of SMA develop from the loss of lower motor neurons, that in turn, causes muscle weakness and atrophy, hypotonia, decreased or absent reflexes, and twitching of muscle fibers. The severity of these symptoms ranges greatly depending on the type; from being fatal within the first year or two, to being almost asymptomatic.

SMA type 0 develops before birth and causes severe weakness and hypotonia, joint deformity and tightening (contractures), and congenital heart defects. Infants do not achieve developmental motor milestones.

  • SMA type 1 affects approximately 60% of infants born with SMA and causes severe weakness, poor suck and swallow reflexes, and respiratory muscle weakness. Without intervention, affected children die before two years of age.
  • SMA type 2 affects 30% of infants born with SMA and usually manifests between 6 and 18 months of age. Patients with SMA type 2 never achieve independent standing and walking.
  • SMA type 3, also known as juvenile SMA or Kugelberg-Welander disease, occurs in about 10% of infants born with SMA. Patients with SMA type 3 have hip and leg weakness and may fall frequently, but can walk independently at some point in their development.
  • SMA type 4, also known as late-onset SMA, occurs in less than 1% of people with SMA. Symptoms are less severe than in other subtypes and onset typically occurs in adulthood and most commonly after 35 years of age.


Spinal Muscular Atrophy (SMA)


Spinal Muscular Atrophy (SMA) Diagnosis

Diagnosis for SMA is typically carried out by physical examination, a complete medical history check, a blood test and in some cases genetic testing.

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Spinal Muscular Atrophy (SMA) Treatments

The treatment of SMA requires a multidisciplinary team approach, including neurologists, medical geneticists, physical therapists, speech pathologists, pulmonologists, respiratory therapists, medical social workers, nutritionists, psychologists and specialized nurses.

Physical & Occupational Therapy

SMA is typically managed utilizing physical therapy, occupational therapy, monitoring respiratory function, diet and nutrition monitoring, spine curvature monitoring and intervention, and in many cases the use of orthotics and adaptive equipment.

Supportive management has been shown to increase comfort and life expectancy.

Medications for SMA Treatment

Advancements in medical research has also led to therapies that can improve the course of SMA. For example, Nusinersen (Spinraza), approved by the FDA in 2016, and onasemnogene abeparvovec-xioi (Zolgensma), approved by the FDA in 2019, both show promise in the treatment of children less than two years of age suffering from SMA.

Have questions?

Spinal Muscular Atrophy Frequently Asked Questions

SMA has a reported frequency of 1:6,000-1:10,000 worldwide, and is estimated to affect approx 10,000-25,000 children in the U.S.A.

SMA is categorized into 5 different sub groups, these include:

  • SMA type 0 (prenatal SMA)
  • SMA type 1 (infantile SMA, Werdnig-Hoffmann disease)
  • SMA type 2 (intermediate SMA, Dubowitz disease)
  • SMA type 3 (juvenile SMA, Kugelberg-Welander disease)
  • SMA type 4 (late onset SMA)

Symptoms of SMA typically include: weakness in the arms and legs, difficulty moving, twitching or shaking of the muscles (tremors), joint problems, difficulty breathing and/or swallowing.

Depending on the type, life expectancy can vary greatly. Those with Type 1 SMA usually do not survive past the 1st or 2nd birthday. Around 70% of patients with Type 2 SMA live to the age of 25, and those with Type 3 or Type 4 often live full lives with treatment.

Talk to your doctor about support groups for SMA, both locally and, more likely, online. Whilst SMA is rare, the online medical community can help patients connect with others from around world, which greatly increases the collective knowledge these support groups can offer.

Remember not to believe every thing you read on the Internet, and be sure to join, follow, and participate in reputable support groups, most of which will have government support.

  • Some great online resources for rare diseases include:
  • https://www.webmd.com
  • https://medlineplus.gov/
  • https://rarediseases.info.nih.gov/
  • https://my.clevelandclinic.or
  • https://www.orpha.net/consor/cgi-bin/Disease.php?lng=EN
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