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HelpTest Code LAB1912 Spinal Muscular Atrophy (SMN1 & SMN2) Copy Number by MLPA
Clinical System Name
Spinal Muscular Atrophy (SMN1 & SMN2) Copy Number by MLPA
Synonyms
SMA Dosage Analysis
Spinal Muscular Atrophy, Diagnostic Test
SMA 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
Note: For patients who have had a whole blood transfusion, wait 10 days post transfusion to draw for genetic testing. No wait time is necessary for blood or saliva collection if the patient received leuko-reduced red cells or plasma.
Specimen: Whole blood
Container(s): Lavender/EDTA
Preferred Vol: 3 mL
Minimum Vol: 1 mL
Note: Heparin samples (Green tops) are unacceptable.
Specimen: DNA extracted from EDTA blood by our Seattle Children’s Laboratory is accepted.
DNA extracted from EDTA blood by other clinical laboratories may be accepted at the discretion of the laboratory director. Please contact LabDNABank@seattlechildrens.org prior to sending extracted DNA.
Minimum: 5µg
Note: Isolation of nucleic acids for clinical testing must be performed in a CLIA-certified
laboratory or a laboratory meeting equivalent requirements as determined by the CAP
and/or the CMS. DNA concentration minimum 100 µg/mL; 260/280 ratio 1.70-2.00
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
CPT Codes
81329 (updated 3/27/19 by jnaray)
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.
Reference Range
Interpretive report will be provided
Requisition
Special Instructions
Links to: Spinal Muscular Atrophy GeneReviews
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.