| Test Name: |
*RETIRED* SPINAL MUSCULAR ATROPHY CARRIER TESTING (SMA) |
| Test Code: |
2198701 |
| Alias: |
Arthron-ryposis Multiplex Congenita (Prenatal SMA)
Congenital Axonal Neurotherapy
Dubowitz Disease (SMA Type II)
Kugelberg-Welander Disease (SMA Type III)
LAB10620
SMN1 Copy-number Analysis
Werdnig-Hoffmann Disease (SMA Type I)
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| CPT Code(s): |
81329
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| Test Includes: |
*Note: This test may require notification/prior authorization by insurance companies. Check the patient's insurance plan for qualifications prior to submitting testing. If authorization is required, please submit with the test request. |
| Preferred Specimen: |
Adults: 10 mL whole blood; 20 mL whole blood if ordering multiple tests |
| Container: |
Whole blood: Yellow-top (ACD-A) tube (preferred) or lavender-top (EDTA) tube
Yellow-top (ACD-B) tube is not acceptable |
| Alternate Container: |
Whole blood: 3 - EDTA (lavender), fill tubes until stopping point; do not combine with other testing |
| Transport Temperature: |
Room temperature |
| Stability: |
Room Temperature: 4 days
Refrigerated: Unacceptable
Frozen: Unacceptable |
| Rejection Criteria: |
Frozen or hemolyzed specimen; quantity not sufficient for analysis; blood specimens more than four days post draw |
| Limitations: |
This copy number analysis does not detect individuals who are carriers of SMA as a result of either two (or very rarely three) copies of the SMN1 gene on one chromosome and the absence of the SMN1 gene on the other chromosome; or germline mosaicism; or small intragenic mutations within the SMN1 gene; or mutations in genes other than SMN1. False-positive results or false-negative results may occur for reasons that include genetic variants, blood transfusions, bone marrow transplantation, erroneous representation of family relationships, or contamination of a fetal sample with maternal cells. |
| Additional Information: |
Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disorder with variable age at onset and severity, characterized by progressive degeneration of the lower motor neurons in the spinal cord and brain stem, leading to muscle weakness, and in its most common form, respiratory failure by age two. Complications of SMA may include poor weight gain, sleep difficulties, pneumonia, scoliosis, and joint deformities. In severely affected individuals, abnormal fetal ultrasound findings may include congenital joint contractures, polyhydramnios, and decreased fetal movement.3 Treatment is supportive. Targeted therapies may be available for some individuals. Approximately 94% of affected individuals have 0 copies of the SMN1 gene; in these individuals an increase in the number of copies of the SMN2 gene correlates with reduced disease severity. |
| Schedule: |
TAT: Report in 7-13 days from receipt of specimen at LabCorp |
| Method: |
The copy number of SMN1 exon 7 is assessed relative to internal standard reference genes by quantitative polymerase chain reaction (qPCR). A mathematical algorithm calculates 0, 1, 2 or 3 copies with statistical confidence. When no copies of SMN1 are detected, the primer and probe binding sites are sequenced to rule out variants that could interfere with copy number analysis and SMN2 copy number is assessed by digital droplet PCR analysis relative to an internal standard reference gene. Individuals with one copy of SMN1 are predicted to be carriers of SMA; those with two or more copies have a reduced carrier risk. For carrier screening, when two copies of SMN1 are detected, allelic discrimination qPCR targeting c.*3+80T>G in SMN1 is performed. The presence or absence of c.*3+80T>G correlates with an increased or decreased risk, respectively, of being a silent carrier (2+0).. |
| Performing Lab: |
LabCorp; #450010 |
| Clinical Significance: |
Carrier testing for individuals in the general population, or individuals with a family history of SMA, or couples who are planning a pregnancy or who are already pregnant. Pediatric or adult diagnostic testing when a diagnosis of SMA is suspected. Test 452140, Prenatal Spinal Muscular Atrophy (SMA) Testing, should be used for prenatal diagnosis for at-risk pregnancies, when both parents are carriers or when severe joint contractures are found on fetal ultrasound. |
| Use: |
Updated 02/17/22 |
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Health Lab Test Code Build Information
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The CPT codes included in this publication are in accordance with Current Procedural Terminology, a publication of the American Medical Association. CPT codes are provided here for the convenience of our clients; however, correct coding often varies from one carrier to another, and HealthLab may bill specific carriers using codes other than those shown. Clients who bill for services should verify the code(s) with the applicable payor to confirm that their use is appropriate in each case.
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