A young boy in a wheelchair with a woman.
Different types of SMA are diagnosed at different stages in life.

What Each Diagnosis of SMA Involves

Spinal Muscular Atrophy (SMA) is a genetic disease that impacts the part of the nervous system that controls bodily movements. SMA involves the loss of motor neurons that send messages from the brain to control movement. SMA is a progressive condition that is classified by the age of onset, symptoms and the speed at which the condition worsens.

Typical symptoms associated with SMA include:

  • Muscle weakness
  • Floppiness
  • Tremors
  • Joint stiffness
  • Muscle pain
  • Difficulty breathing
  • Problems with swallowing
  • Scoliosis

However, the severity and presence of each symptom can vary greatly based on the type of SMA a person is diagnosed with. The rule of thumb is that the condition is more aggressive if it presents itself earlier in life.

SMA Type 1

SMA Type 1, also known as Werdnig-Hoffmann Disease, is the most common form of SMA. This particular condition accounts for 50-70% of childhood SMA. Unfortunately, it also happens to be the most severe type of the disease and 68% of children with this form of SMA die before their first birthday while over 80% pass away before their fourth birthday.

Children with Type 1 SMA show signs of muscle weakness, reduced muscle tone and issues with movement between the ages of 0-6 months of age. Patients with this condition cannot sit without support, and they never gain this ability because the disease only progresses with time.

Usually, the condition is first noticed by parents as their children do not meet certain physical milestones during their development.

However, medical professionals are dedicated to better understanding this particular type of SMA. Survival rates have seen some improvements as more research is conducted in regards to nutrition and respiratory care.

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SMA Type 2

SMA Type 2, also known as Dubowitz Disease, typically impacts patients between the ages of 7-18 months old. Individuals with this condition usually live into adulthood, and with proper care, many can live well into their later adult years. Proper nutrition and respiratory care incredibly important with this particular type of SMA.

While this particular type is considered less aggressive than Type 1, it also poses serious health concerns as the patient ages. Usually, patients will develop a curved backs (scoliosis) as they age and will struggle with swallowing and breathing. Muscle tremors and floppiness are also common symptoms of this type.

Muscle loss is experienced from birth, but the slower progression allows them to gain the ability to sit. Very few people with Type 2 SMA learn to walk.

SMA Type 3

SMA Type 3, also known as Kugelberg-Welander Disease, usually impacts children over the age of 18 months old and can even wait to present itself until the child is well into their adolescence or even young adulthood.

Individuals with this particular type of SMA can usually walk, but may experience difficulty with balance or have issues with running or completing other physical tasks. Usually, legs are more impacted than the arms.

Unfortunately, children who are diagnosed early with SMA Type 3 typically lose their ability to walk once they enter their early teens. However, some people are able to continue walking with assistance. Typically, individuals with this condition are encouraged to participate in certain strength-training exercises to maintain their ability to walk as long as possible.

Fortunately, people with this condition have a normal life expectancy and generally do not experience any swallowing or breathing issues that are commonly associated with other types of SMA.
While this particular type is considered less severe, regular medical check-ups are necessary to monitor the progression of the condition closely.

SMA Type 4

SMA Type 4, adult-onset SMA, usually impacts adults between the ages of 20-30 years old. Muscle tremors, weakness and scoliosis are common symptoms of this particular type of SMA. Typically, medical professionals suggest a strength training program to help manage some of the symptoms and to help slow the progression.

While life expectancy is considered normal with SMA Type 4, usually individuals will need assistance with walking by the time they reach 60 years old. The progression of this type is considered slow, and symptoms usually range from mild to moderate. However, it is still important to have regular physicals to track the progression of the condition throughout your life.


SMA is a progressive disease that can certainly impact the quality of life of patients. However, as you can see, there are a variety of types of this condition that range considerably in severity and prognosis. However, it is also important to note that up to 25% of individuals do not perfectly fit into any category of SMA types.

Keep in mind, the progression and severity of symptoms can vary greatly from person to person.

If you would like more information about SMA and the various types, reach out to your medical professional today for more information.