Spinal Muscular Atrophy (SMA) Carrier Testing

CPT: 81401. If reflex testing is performed, concomitant CPT codes/charges will apply.
Updated on 11/17/2018
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Test Details

Synonyms

  • SMN1 Copy-number Analysis
  • Arthron-ryposis Multiplex Congenita (Prenatal SMA)
  • Congenital Axonal Neurotherapy
  • Dubowitz Disease (SMA Type II)
  • Kugelberg-Welander Disease (SMA Type III)
  • Werdnig-Hoffmann Disease (SMA Type I)

Use

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. Prenatal diagnosis for at-risk pregnancies, when both parents are carriers or when severe joint contractures are found on fetal ultrasound.

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.

Methodology

After DNA is isolated, exon 7 of the SMN1 gene and internal standard reference genes are amplified by real-time polymerase chain reaction (PCR). A mathematical algorithm calculates SMN1 copy numbers of 0, 1, 2, or 3 with statistical confidence. To rule out the presence of sequence variants that could interfere with analysis and interpretation, sequence analysis of primer and probe binding sites is performed for postnatal samples with one copy of SMN1 and for all fetal samples. Reflex testing to SMN2 copy number analysis is performed for affected fetus with 0 copies of SMN1.

Additional Information

Spinal muscular atrophy (SMA) is an autosomal recessive disease caused by deletions or, less often, point mutation(s) in the SMN1 gene, leading to a reduction in the amount of survival motor neuron (SMN) protein. SMA is characterized by the progressive degeneration of the lower motor neurons, leading to muscle weakness and, in the most common type, respiratory failure by age two. Muscles responsible for crawling, walking, swallowing, and head and neck control are the most severely affected. The SMN2 gene is adjacent to SMN1 and encodes low levels of the SMN protein. An increase in SMN2 copy number (3+) may reduce disease severity among affected individuals.

Specimen Requirements

Specimen

Whole blood

Whole blood, cultured amniotic fluid, or cultured chorionic villus sample (CVS)

Whole blood

Volume

Adults: 10 mL whole blood; 30 mL whole blood if ordering multiple tests

Adults: 10 mL whole blood; 30 mL whole blood if ordering multiple tests. Amniotic fluid: One T-25 flask of confluent cells. CVS: One T-25 flask of confluent cells. If cultured at another facility please maintain back-up cultures.

Adults: 10 mL whole blood; 30 mL whole blood if ordering multiple tests

Storage Instructions

Maintain specimen at room temperature.

Causes for Rejection

Frozen or hemolyzed specimen; quantity not sufficient for analysis; blood specimens more than three days post draw

Clinical Information

Special Instructions

For prenatal testing, please refer to test code 452140, Prenatal Spinal Muscular Atrophy (SMA) Testing.

For prenatal testing: LabCorp clients call 800-345-4363, Integrated Genetics clients call 800-848-4436 to speak to a laboratory genetic coordinator before collecting specimens. In some circumstances, specimens from other family members may be required. All prenatal specimens (including cord blood) must be accompanied by a maternal blood or mouthwash specimen for analysis of the specimen for possible maternal cell contamination. Cultures are required for prenatal SMA testing.

For prenatal testing, please refer to test code 452140, Prenatal Spinal Muscular Atrophy (SMA) Testing.

LOINC® Map

Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
450010 SMN1 Copy Number Analysis 450001 Genetic Counselor: N/A
450010 SMN1 Copy Number Analysis 450002 Client Specimen ID: 48767-8
450010 SMN1 Copy Number Analysis 450003 Specimen Type: 31208-2
450010 SMN1 Copy Number Analysis 450004 Specimen(s) Received: 74384-9
450010 SMN1 Copy Number Analysis 450005 Clinical Data: 42349-1
450010 SMN1 Copy Number Analysis 450006 Ethnicity: 42784-9
450010 SMN1 Copy Number Analysis 450007 SMA Results: 41053-0
450010 SMN1 Copy Number Analysis 450008 SMA Interpretation: 35462-1
450010 SMN1 Copy Number Analysis 450009 Comments: 48767-8
450010 SMN1 Copy Number Analysis 450111 Carrier Detection Rate: N/A
450010 SMN1 Copy Number Analysis 450011 Method/Limitations: 49549-9
450010 SMN1 Copy Number Analysis 450012 References: 69549-4
450010 SMN1 Copy Number Analysis 450013 Disclaimer: 62364-5
450010 SMN1 Copy Number Analysis 450014 Electronically Signed by: N/A
450010 SMN1 Copy Number Analysis 450015 SMN1 Copy Number Analysis PDF 51969-4
Reflex Table for SMA Results:
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 451790 SMN2 Copy Number Reflex 451788 SMN2 Copy Number Reflex 54449-4

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