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Test Code SMACARRIER Spinal Muscular Atrophy, Carrier Test

Clinical System Name

SMA Carrier Testing Request

Synonyms

SMA Dosage Analysis

 

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

 

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: Cultured cells

Acceptable:  Fibroblasts

Container(s): T-25 flasks

Preferred Vol: 2 flasks

Processing Instructions

Reject due to: Heparin, extracted DNA

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
Cultured cells Room temp 3 days
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

Reference Range

Interpretive report will be provided

Methodology

Method: Multiple ligation-dependent probe amplification (MLPA) of exons 7&8 in the survival motor neuron 1 (SMN1) gene.

CPT Codes

81401 (updated 2/2/16 by jconta)

Special Instructions

Links to:  Spinal Muscular Atrophy GeneReviews

Requisition

Molecular Genetics

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.