Back ضمور العضلات الشوكي Arabic Spinalna mišićna atrofija BS Atròfia muscular espinal Catalan Spinální svalová atrofie Czech Spinal muskulær atrofi Danish Spinale Muskelatrophie German Νωτιαία μυϊκή ατροφία Greek Atrofia muscular espinal Spanish آتروفی عضلانی نخاعی Persian Spinaalinen lihasatrofia Finnish

Spinal muscular atrophy

This article is about the genetic disorder associated with the SMN1 gene on chromosome 5q. For a list of conditions with similar names, see Spinal muscular atrophies.

Spinal muscular atrophy
Other namesAutosomal recessive proximal spinal muscular atrophy, 5q spinal muscular atrophy
Location of neurons affected by spinal muscular atrophy in the spinal cord
SpecialtyNeurology
SymptomsProgressive muscle weakness[1]
ComplicationsScoliosis, joint contractures, pneumonia[2]
Usual onsetMutation is congenital, symptoms start varies by type
DurationLifelong
TypesType 0 to type 4[2]
CausesMutation in SMN1[2]
Diagnostic methodGenetic testing[1]
Differential diagnosisCongenital muscular dystrophy, Duchenne muscular dystrophy, Prader-Willi syndrome[2]
TreatmentSupportive care, medications[1]
MedicationNusinersen, onasemnogene abeparvovec, Risdiplam
PrognosisVaries by type[2]
Frequency1 in 10,000 people[2]

Spinal muscular atrophy (SMA) is a rare neuromuscular disorder that results in the loss of motor neurons and progressive muscle wasting.[3][4][5] It is usually diagnosed in infancy or early childhood and if left untreated it is the most common genetic cause of infant death.[6] It may also appear later in life and then have a milder course of the disease. The common feature is progressive weakness of voluntary muscles, with arm, leg and respiratory muscles being affected first.[7][8] Associated problems may include poor head control, difficulties swallowing, scoliosis, and joint contractures.[2][8]

The age of onset and the severity of symptoms form the basis of the traditional classification of spinal muscular atrophy into a number of types.[4]

Spinal muscular atrophy is due to an abnormality (mutation) in the SMN1 gene[1][2] which encodes SMN, a protein necessary for survival of motor neurons.[8] Loss of these neurons in the spinal cord prevents signalling between the brain and skeletal muscles.[8] Another gene, SMN2, is considered a disease modifying gene, since usually the more the SMN2 copies, the milder is the disease course. The diagnosis of SMA is based on symptoms and confirmed by genetic testing.[9][1]

Usually, the mutation in the SMN1 gene is inherited from both parents in an autosomal recessive manner, although in around 2% of cases it occurs during early development (de novo).[1][10] The incidence of spinal muscular atrophy worldwide varies from about 1 in 4,000 births to around 1 in 16,000 births,[11] with 1 in 7,000 and 1 in 10,000 commonly quoted for Europe and the US respectively.[2]

Outcomes in the natural course of the disease vary from death within a few weeks after birth in the most acute cases to normal life expectancy in the protracted SMA forms.[8] The introduction of causative treatments in 2016 has significantly improved the outcomes. Medications that target the genetic cause of the disease include nusinersen, risdiplam,[12] and the gene therapy medication onasemnogene abeparvovec. Supportive care includes physical therapy, occupational therapy, respiratory support, nutritional support, orthopaedic interventions, and mobility support.[1]

  1. ^ a b c d e f g "Spinal muscular atrophy". Genetic and Rare Diseases Information Center (GARD) – an NCATS Program. Retrieved 27 May 2019.
  2. ^ a b c d e f g h i "Spinal Muscular Atrophy". NORD (National Organization for Rare Disorders). Retrieved 27 May 2019.
  3. ^ "Spinal muscular atrophy". nhs.uk. 23 October 2017. Retrieved 24 October 2020.
  4. ^ a b "Spinal muscular atrophy: MedlinePlus Genetics". medlineplus.gov. Retrieved 24 October 2020.
  5. ^ "Spinal Muscular Atrophy (SMA) | Boston Children's Hospital". www.childrenshospital.org. Retrieved 25 October 2020.
  6. ^ "FDA approves innovative gene therapy to treat pediatric patients with spinal muscular atrophy, a rare disease and leading genetic cause of infant mortality". FDA. 24 May 2019. Retrieved 27 May 2019.
  7. ^ "Spinal Muscular Atrophy Fact Sheet | National Institute of Neurological Disorders and Stroke". NINDS. Retrieved 27 May 2019.
  8. ^ a b c d e "Spinal muscular atrophy". Genetics Home Reference. Retrieved 27 May 2019.
  9. ^ "Spinal Muscular Atrophy – Conditions | Children's National". childrensnational.org. Retrieved 25 October 2020.
  10. ^ Prior, Thomas W.; Leach, Meganne E.; Finanger, Erika (1993), Adam, Margaret P.; Ardinger, Holly H.; Pagon, Roberta A.; Wallace, Stephanie E. (eds.), "Spinal Muscular Atrophy", GeneReviews®, Seattle (WA): University of Washington, Seattle, PMID 20301526, retrieved 25 October 2020
  11. ^ Verhaart, Ingrid E. C.; Robertson, Agata; Leary, Rebecca; McMacken, Grace; König, Kirsten; Kirschner, Janbernd; Jones, Cynthia C.; Cook, Suzanne F.; Lochmüller, Hanns (July 2017). "A multi-source approach to determine SMA incidence and research ready population". Journal of Neurology. 264 (7): 1465–1473. doi:10.1007/s00415-017-8549-1. ISSN 0340-5354. PMC 5502065. PMID 28634652.
  12. ^ US9879007B2, Qi, Hongyan; Choi, Soongyu & Dakka, Amal et al., "Compounds for treating spinal muscular atrophy", issued 2018-01-30 
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