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HelpTest Code LAB1911 Spinal Muscular Atrophy Carrier Test
Clinical System Name
SMA Carrier Testing
Description
Spinal muscular atrophy (SMA) causes progressive muscular weakness and degeneration by loss of anterior horn cells in the brain stem and spinal cord. This carrier test is a dosage analysis to asses the SMN1 gene for deletions or duplications. This test will detect approximately 87-95% of SMA carriers in the non-Black population and 71% among the Black population.
This test can be used for:
- Carrier testing for individuals with a family history of SMA.
- Carrier testing for individuals in the general population.
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, 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.
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 | 2-3 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 the survival motor neuron 1 (SMN1) gene.
Reference Range
Interpretive report will be provided
Requisition
Special Instructions
Links to: Spinal Muscular Atrophy GeneReviews
Clinical Utility
This is a carrier test for spinal muscular atrophy (SMA). Dosage analysis is performed to asses the SMN1 gene for deletions or duplications.
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 as 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.
SMN-related SMA is inherited in an autosomal recessive manner. Carriers for this condition have one chromosome 5 with no functional copy of SMN1 and one chromosome 5 with one or more functional copies of SMN1. This test will detect SMA carriers who have a SMN1 deletion on one chromosome 5 and just one copy of SMN1 on the other chromosome 5. This test will not detect SMA carriers who have a SMN1 deletion on one chromosome 5 and two or more copies of SMN1 on the other chromosome 5. This test will detect approximately 87-95% of SMA carriers in the non-Black population and 71% among the Black population (ref. 1). SMN1 point mutations will not be detected by this test. Pre-test genetic counseling is recommended.
1. MacDonald WK, Hamilton D, Kuhle S. SMA carrier testing: a meta-analysis of differences in test performance by ethnic group. Prenat Diagn. 2014; 34(12):1219-1226.