Click on the tabs below to learn more about the different types of SMA.
Unable to sit
≤ 2 years
Type 1 (also known as Werdnig-Hoffmann disease)
Hypotonia and impaired head control
“Frog leg” presentation
Swallowing, feeding, and handling of oral secretion are affected before 1 year of age
Atrophy and fasciculation of the tongue
Weakness and hypotonia in the limbs and trunk
Intercostal muscle weakness (note, the diaphragm is relatively spared)
Bell-shaped trunk with chest wall collapse and abdominal protrusion
Able to sit independently (“sitters”)
> 2 years
70% still living at age 25
Type 2 (also known as Dubowitz disease)
Bulbar weakness with chewing and swallowing difficulties that may lead to poor weight gain
Weak intercostal muscles
Difficulty coughing and clearing tracheal secretion
Fine tremors with extended fingers or when attempting hand grips
Kyphoscoliosis, or scoliosis requiring bracing or spinal surgery
Able to walk independently (“walkers” - although they
may progressively lose this ability)
Type 3 (also known as Kugelberg-Welander disease)
Cough, and nocturnal hypoventilation
Joint overuse symptoms
Physical symptoms are similar to juvenile-onset SMA, with the gradual onset of weakness, tremor, and muscle twitching first noted in late teens or adulthood
You may notice that these characteristics of SMA are more commonly grouped by Type I-IV in internet articles or clinical research.
Learn more on how different aspects of care may relate to the signs and symptoms of SMA
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