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Spinal Muscular Atrophy - Description
ICD-9
335, Spinal muscular atrophy, unspecified
See SMA ICD9
(
72 KB)
for a detailed code list. 335 is not a specific code and should not be used by itself.
Description
Spinal muscular atrophy (SMA) is an autosomal recessive disorder that causes decreased survival of the anterior horn cells – motor neurons – that innervate voluntary muscles, resulting in progressive muscle atrophy and weakness. However, as more is learned about SMA, it is becoming increasingly clear that motor neurons are not the only part of the body affected. [Shanmugarajan: 2007] SMA is traditionally classified by age of onset and severity, however some experts classify by functional levels (non-sitters, sitters, and walkers) as which correlate better with clinical care needs than the traditional classification. [Wang: 2007] Clinical characteristics often overlap between types.- Type I SMA (Werdnig-Hoffman ) presents near birth; these children never learn to sit or walk and have severe respiratory and swallowing problems, including difficulty handling oral secretions, and a significantly shortened life span. Risk of death in infancy is high, and most survivors are ventilator dependent by two years of age. Other features include poor head control, a bell-shaped chest, weak cry and cough, tongue atrophy and fasciculation, and paradoxical breathing.
- Type II SMA presents later in the first year of life or up to about two years of age. These children usually learn to sit. They often have respiratory and swallowing problems, including difficulty gaining weight due to bulbar muscle weakness, weak cough and night-time hypoventilation. Swallowing problems and difficulties opening the jaw widely have been shown to contribute to malnutrition in children with SMA II. [Messina: 2008] A tremor may be noted in these children. Joint contractures and scoliosis develop over time in nearly all affected children, and warranting proactive intervention.
- Type III SMA (Kugelberg-Welander) presents later in childhood or adolescence and these children usually sit and walk (although some may lose this ability over time) and have fewer problems with respiratory function and swallowing. Scoliosis and contractures as well as joint pain are often noted in older children.
- Infants with type 0 SMA present before birth, with decreased fetal movement noted around 30 weeks of age. They are hypotonic at birth with swallowing and breathing problems and, in some infants, arthrogryposis.
- Type IV SMA presents in adults and will not be discussed further here.
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Left image: 5 month old girl with SMA Type I Middle image: Boy with SMA Type II with turtleshell and AFOs Right image: Boy with SMA Type III being checked for hip girdle weakness |
Genetics
SMA results from a missing or defective protein called motor neuron survival protein (SMN protein). This protein is coded for by a gene, SMN1, located on the long arm of chromosome 5, which in most cases of SMA contains deletions in various combinations of exons 7 or 7 and 8. A copy of the SMN1 gene, called SMN2, which is very similar to SMN1 is also located on chromosome 5, and may alter the severity of the SMA. (see Initial Diagnosis page for genetic testing information and Genetics of Spinal Muscular Atrophy for more information). The SMN protein complex appears to be involved in the biogenesis of specific ribonucleoproteins. [Kolb: 2007] [Sumner: 2007].Prognosis
Depends on the type. Most children with type I SMA who do not receive ventilatory support die in infancy, with respiratory failure in the setting of infection being the leading cause of death. [Cobben: 2008] [Bach: 2007] Individuals with SMA III have much longer life spans. For details about prognosis for each type, see [Chung: 2004]Prevalence
SMA occurs in approximately 1 in every 6000 births. About 1 in every 40 people are genetic carriers. [Cusin: 2003] SMA I is the leading inherited cause of infant mortality. Newborn screening for SMA may be available in the (near) future.Pearls And Alerts
On Treatment And Management Page
Questions regarding treatment of children with SMA
Helpful Articles
PubMed search on spinal muscular atrophy: articles over the last 2 years
Oskoui M, Kaufmann P.
Spinal muscular atrophy.
Neurotherapeutics.
2008;5(4):499-506.
PubMed abstract
Farrar MA, Johnston HM, Grattan-Smith P, Turner A, Kiernan MC.
Spinal muscular atrophy: molecular mechanisms.
Curr Mol Med.
2009;9(7):851-62.
PubMed abstract
Chad T.
Losing a child to spinal muscular atrophy.
Paediatr Nurs.
2008;20(3):32-3.
PubMed abstract
Mannaa MM, Kalra M, Wong B, Cohen AP, Amin RS.
Survival probabilities of patients with childhood spinal muscle atrophy.
J Clin Neuromuscul Dis.
2009;10(3):85-9.
PubMed abstract
Rudnik-Schöneborn S, Berg C, Zerres K, Betzler C, Grimm T, Eggermann T, Eggermann K, Wirth R, Wirth B, Heller R.
Genotype-phenotype studies in infantile spinal muscular atrophy (SMA) type I in Germany: implications for clinical trials
and genetic counselling.
Clin Genet.
2009;76(2):168-78.
PubMed abstract
Cobben JM, Lemmink HH, Snoeck I, Barth PA, van der Lee JH, de Visser M.
Survival in SMA type I: a prospective analysis of 34 consecutive cases.
Neuromuscul Disord.
2008;18(7):541-4.
PubMed abstract
Spinal Muscular Atrophy Module Authors
| Authors: | Lynne M Kerr MD, PhD, 2/2011 Kathy Swoboda MD, 2/2011 |
| Content Last Updated: | 2/2011 |
The authors listed above are responsible for the overall Spinal Muscular Atrophy Module. Authors contributing to individual pages in the module are listed on those pages.
Page Bibliography
Bach JR, Saltstein K, Sinquee D, Weaver B, Komaroff E.
Long-term survival in Werdnig-Hoffmann disease.
Am J Phys Med Rehabil.
2007;86(5):339-45 quiz 346-8, 379.
PubMed abstract
Chung BH, Wong VC, Ip P.
Spinal muscular atrophy: survival pattern and functional status.
Pediatrics.
2004;114(5):e548-53.
PubMed abstract
Cobben JM, Lemmink HH, Snoeck I, Barth PA, van der Lee JH, de Visser M.
Survival in SMA type I: a prospective analysis of 34 consecutive cases.
Neuromuscul Disord.
2008;18(7):541-4.
PubMed abstract
Cusin V, Clermont O, Gérard B, Chantereau D, Elion J.
Prevalence of SMN1 deletion and duplication in carrier and normal populations: implication for genetic counselling.
J Med Genet.
2003;40(4):e39.
PubMed abstract / Full Text
Kolb SJ, Battle DJ, Dreyfuss G.
Molecular functions of the SMN complex.
J Child Neurol.
2007;22(8):990-4.
PubMed abstract
Messina S, Pane M, De Rose P, Vasta I, Sorleti D, Aloysius A, Sciarra F, Mangiola F, Kinali M, Bertini E, Mercuri E.
Feeding problems and malnutrition in spinal muscular atrophy type II.
Neuromuscul Disord.
2008;18(5):389-93.
PubMed abstract
Shanmugarajan S, Swoboda KJ, Iannaccone ST, Ries WL, Maria BL, Reddy SV.
Congenital bone fractures in spinal muscular atrophy: functional role for SMN protein in bone remodeling.
J Child Neurol.
2007;22(8):967-73.
PubMed abstract
Sumner CJ.
Molecular mechanisms of spinal muscular atrophy.
J Child Neurol.
2007;22(8):979-89.
PubMed abstract
Wang CH, Finkel RS, Bertini ES, Schroth M, Simonds A, Wong B, Aloysius A, Morrison L, Main M, Crawford TO, Trela A.
Consensus statement for standard of care in spinal muscular atrophy.
J Child Neurol.
2007;22(8):1027-49.
PubMed abstract