Types of SMA

TYPES OF

Spinal Muscular Atrophy (SMA)

The age of onset, severity of symptoms and the level at which functional ability is affected, determine the type of SMA of each patient. Every person with SMA is affected differently, and up to 25% of those diagnosed with SMA cannot be clearly assigned to a specific type.¹

CHARACTERISTICS OF SMA

Click on the tabs below to learn more about the different types of SMA.

Highest motor milestone achieved

Unable to sit
(“non-sitters”)

Life expectancy

≤ 2 years

SMA Type

Type 1 (also known as Werdnig-Hoffmann disease)

CLINICAL CHARACTERISTICS:

Hypotonia and impaired head control
“Frog leg” presentation
Weak cry
Weak cough
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)
Paradoxical breathing
Bell-shaped trunk with chest wall collapse and abdominal protrusion

Highest motor milestone achieved

Able to sit independently (“sitters”)

Life expectancy

> 2 years
70% still living at age 25

SMA Type

Type 2 (also known as Dubowitz disease)

CLINICAL CHARACTERISTICS:

Bulbar weakness with chewing and swallowing difficulties that may lead to poor weight gain
Weak intercostal muscles
Diaphragmatic breathing
Difficulty coughing and clearing tracheal secretion

Fine tremors with extended fingers or when attempting hand grips
Kyphoscoliosis, or scoliosis requiring bracing or spinal surgery
Joint contractures

Highest motor milestone achieved

Able to walk independently (“walkers” - although they
may progressively lose this ability)

Life expectancy

Normal

SMA Type

Type 3 (also known as Kugelberg-Welander disease)

CLINICAL CHARACTERISTICS:

Scoliosis
Swallowing difficulty
Cough, and nocturnal hypoventilation

Muscle aching
Joint overuse symptoms

Highest motor milestone achieved

All

Life expectancy

Normal

SMA Type

Type 4

CLINICAL CHARACTERISTICS:

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

Note:

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

Care Approaches

SMA in Children

SMA in Adults

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References

1. Kolb SJ, Kissel JT. Spinal muscular atrophy. Arch Neurol 2011;68(8):979-984.

2. Prior TW, Russman BS. Spinal muscular atrophy. NCBI Bookshelf [online] 2013 Nov 14 [cited 2016 Apr 15]. Available from: URL: http://www.ncbi.nlm.nih.gov/books/NBK1352/?report=printable.

3. Mercuri E, et al. Diagnosis and management of spinal muscular atrophy: Part 1: Recommendations for diagnosis, rehabilitation, orthopedic and nutritional care. Neuromuscl Disord 2018;28(2):103-115.

4. Markowitz JA, Singh P, Darras BT. Spinal muscular atrophy: a clinical and research update. Pediatr Neurol 2012;46(1):1-12.

5. Darras BT, Royden Jones H Jr, Ryan MM, De Vivo DC, eds. Neuromuscular Disorders of Infancy, Childhood, and Adolescence: A Clinician’s Approach. 2nd ed. London, UK: Elsevier; 2015.

6. Lunn MR, Wang CH. Spinal muscular atrophy. Lancet 2008;371(9630):21‌20-21‌33.

7. Online Mendelian Inheritance in Man. Spinal muscular atrophy, Type III; SMA3. [online] 2013 Feb 7 [cited 2016 Apr 26]. Available from: URL: http://www.omim.org/entry/253400.

8. Kolb SJ, Kissel JT. Neurol Clin. 2015;33:831-846.

9. D’Amico A, Mercuri E, Tiziano FD, Bertini E. Spinal muscular atrophy. Orphanet J Rare Dis 2011;6:71.