Spinal muscular atrophy diagnosis

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Editors-in-Chief: C. Michael Gibson, M.S., M.D.; Priyamvada Singh, MBBS

## Diagnostics methods

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The diagnosis of SMA is done by a combination of different methods. The commonly used methods are – Genetic testing, blood tests (Enzyme levels), Nerve conduction study, Needle EMG, muscle biopsy. In order to be diagnosed with Spinal muscular atrophy, symptoms need to be present. In most cases a diagnosis can be made by the SMN gene test, which determines whether there is at least one copy of the SMN1 gene by looking for its unique sequences (that distinguish it from the almost identical SMN2) in exons 7 and 8. In some cases, when the SMN gene test is not possible or does not show any abnormality, other tests such as an electromyography (EMG) or muscle biopsy may be indicated.

Genetic testing\- It is currently performed with PCR-based targeted mutation analysis using a restriction enzyme that digests exon 7 (the specific area of chromosome 5 that is affected in the disease). This test can diagnose SMA patients who are homozygous deleted (both allele deleted), compound heterozygotes (deletion in one SMN1 allele and an intragenic point mutation in the other) [1].

Creatine Kinase (CK) – SMA patients may have 2-4 fold serum CK elevation.

Nerve conduction studies \- May show decreased compound motor action potential (CMAP) amplitudes [2].

Needle EMG\- In needle EMG a thin needle electrode is inserted into the muscle. The electrode on the needle picks up the electrical activity of the muscles. This electrical activity is displayed on a monitor called an oscilloscope or heard through a speaker. The presence, size, and shape of the action potential provides information about muscle's ability to respond when the nerves are stimulated. It Shows denervation in SMA I patients without evidence of reinnervation changes [3].

Muscle biopsy\- shows atrophy of muscle groups.[4].

## References

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1. ↑ Feldkötter M, Schwarzer V, Wirth R, Wienker TF, Wirth B (2002). "Quantitative analyses of SMN1 and SMN2 based on real-time lightCycler PCR: fast and highly reliable carrier testing and prediction of severity of spinal muscular atrophy". Am J Hum Genet. 70 (2): 358–68. doi:10.1086/338627. PMC 419987. PMID 11791208.CS1 maint: Multiple names: authors list (link) CS1 maint: PMC format (link)
2. ↑ Swoboda KJ, Prior TW, Scott CB, McNaught TP, Wride MC, Reyna SP; et al. (2005). "Natural history of denervation in SMA: relation to age, SMN2 copy number, and function". Ann Neurol. 57 (5): 704–12. doi:10.1002/ana.20473. PMID 15852397.CS1 maint: Explicit use of et al. (link) CS1 maint: Multiple names: authors list (link)
3. ↑ Crawford TO. Spinal muscular atrophies. In: Neuromuscular disorders of infancy, childhood, and adolescence: a clinician’s approach. Philadelphia: Butterworth Heinemann; 2003. pp 145-166
4. ↑ Crawford TO. Spinal muscular atrophies. In: Neuromuscular disorders of infancy, childhood, and adolescence: a clinician’s approach. Philadelphia: Butterworth Heinemann; 2003. pp 145-166

## External links

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* Template:NINDS
* SMA Support
* Spinal Muscular Atrophy - Fight SMA \- An international nonprofit dedicated to finding a treatment or cure for spinal muscular atrophy. Visit Fight SMA's website and also the Spinal Muscular Atrophy Blog for the latest news and research information about the leading genetic killer of children under two.
* Families of Spinal Muscular Atrophy \- An international nonprofit dedicated to advancing research and supporting individuals and families with sma. FSMA has a web site with news, information and message boards for individuals to post questions. FSMA is one of the largest US private funders of SMA research and has more than 30 chapters worldwide.FSMA
* SMA Trust \- a UK registered charity working to fund medical research into Spinal Muscular Atrophy
* Jennifer Trust for Spinal Muscular Atrophy \- A national charity in the UK dedicated both to supporting people affected by SMA, and investing in essential research into causes, treatments and eventually a cure for the condition

Template:Diseases of the nervous system

da:Spinal muskulær atrofi de:Spinale Muskelatrophie el:Νωτιαία μυϊκή ατροφία nl:Spinale Musculaire Atrofieën fi:Spinaaliset lihasatrofiat sv:Spinal muskelatrofi

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