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Test Code SMA Spinal Muscular Atrophy, Diagnostic Test

Clinical System Name

 

Spinal Muscular Atrophy, Diagnostic Test

 

Description

Spinal muscular atrophy (SMA) causes progressive muscular weakness and degeneration by loss of anterior horn cells in the brain stem and spinal cord.  Approximately 95-98% of individuals with SMA are homozygous for a deletion of exons 7 & 8 of the SMN1 gene. The remaining 2%-5% of individuals with SMA are compound heterozygotes for a deletion in combination with a point mutation within the SMN1 gene. Increases in SMN2 gene copy number often modify the phenotype.

 

This test will determine the copy number of both the SMN1 and SMN2 genes.

 

This test can be used for: 

  • Diagnostic testing in an individual suspected to have SMA. 

Link for SMA carrier testing.

Sample Requirements

Specimen: Whole blood, cord blood

Container(s): Lavender/EDTA, Yellow/ACD A or B

Preferred Vol: 3 mL

Minimum Vol: 1 mL

 

Note: Heparin samples (Green tops) are unacceptable.

Processing Instructions

Reject due to: Heparin

Spin: No

Aliquot: No

Temp: Refrigerate

Storage location: Molecular Genetics box in CPA refrigerator #2

 

Off-site collection: Refrigerate blood samples until ready to ship.  Transport all sample types at room temperature via overnight shipping.

Stability

Specimen Type Temperature Time
Whole blood Room temp 3-5 days
Whole blood Refrigerated 7 days

 

Note: Whole blood samples > 7days may be submitted to be assessed by our lab for acceptability for testing.

Availability

STAT Performed TAT
Contact lab Monday - Friday 2 weeks

 

Performing Laboratory

Seattle Children's Laboratory

Department

Department:  Molecular Genetics Laboratory

Phone: 206-987-3872

 

Lab Client Services: 206-987-2617

 

Lab Genetic Counselor: LabGC@seattlechildrens.org

Reference Range

Interpretive report will be provided

Methodology

Method: Multiple ligation-dependent probe amplification (MLPA) of exons 7&8 in SMN1 & SMN2 genes.

 

Limitations: 95-98% of individuals with SMA have SMN1 deletions which can be detected using this technique.  The remaining 2-5% of individuals with SMA have a point mutation within the SMN1 gene that is not detected by this test.  

CPT Codes

81401 (updated 6/15/17 by jnaray)

Special Instructions

Links to: Spinal Muscular Atrophy GeneReviews

Requisition

Molecular Genetics

Clinical Utility

Spinal muscular atrophy (SMA) causes progressive muscular weakness and degeneration by loss of anterior horn cells in the brain stem and spinal cord. Age of onset can vary from prenatal onset to adult onset: SMA I, with onset before six months of age; SMA II, with onset between six and 12 months; SMA III, with onset in childhood after 12 months; and SMA IV, with adult onset.

 

Approximately 95-98% of individuals with SMA are homozygous for a deletion of exons 7 & 8 of the SMN1 gene. About 2-5% of individuals with SMA have a deletion on one SMN1 allele and a point mutation on the other allele.

This test does not include SMN1 or SMN2 gene sequencing. For individuals with a high clinical suspicion of SMA with one copy of SMN1 detected, SMN1 sequencing is recommended.  Increases in SMN2 gene copy number often modify the phenotype.