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Geisinger Medical Laboratories Test Catalog
SMA DIAGNOSTIC TEST |
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Geisinger Epic Procedure Code: LAB3524
Geisinger Epic ID: 49730
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SPECIMEN COLLECTION |
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Specimen type: |
Whole blood | |
Preferred collection container: |
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Alternate Collection Container: |
6 mL pink-top K2 EDTA tube
4 mL green/green-top (sodium heparin) tube
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Specimen required: |
4 mL whole blood, minimum volume 2 mL. | |
| SPECIMEN PROCESSING |
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Specimen processing instructions: |
Do not freeze whole blood specimens. Transport at room temperature. | |
Transport temperature: |
Room temperature. | |
Specimen stability: |
Room temperature (preferred): 8 days. Refrigerated: 14 days. Frozen: Unacceptable. | |
Rejection criteria: |
Clotted specimen. Received frozen | |
TEST DETAILS |
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Additional information: |
For prenatal diagnosis with a fetal specimen: 1) parents must be documented carriers of one of the mutations tested; 2) maternal blood or DNA must be available to rule out maternal cell contamination (order test code 10262X); 3) contact genetic counselor before submission. | |
CPT code(s): |
81329 | |
| Note: The billing party has sole responsibility for CPT coding. Any questions regarding coding should be directed to the payer being billed. The CPT codes provided by GML are based on AMA guidelines and are for informational purposes only. | ||
Methodology: |
Allele Specific Real-Time Polymerase Chain Reaction (PCR), ddCt Method |
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Synonyms: |
Spinal Muscular Atrophy Diagnostic, Quest code 16869 SMADIA
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Clinical significance: |
Spinal muscular atrophy (SMA) is one of the most common autosomal recessive diseases. SMA is characterized by the degeneration of the anterior horn cells of the spinal cord which leads to symmetric proximal muscle weakness. The estimated incidence of SMA is 1/6,000 to 1/10,000 live births with a carrier frequency of 1/40 to 1/60. Clinical presentation, mainly based upon age of onset of symptoms, is classified into 4 SMA subtypes: Subtype I, onset before 6 months of age; Subtype II, onset between 6 and 12 months of age; Subtype III, onset in childhood after 12 months of age; And subtype IV, adult onset. Each subtype displays significant variance of clinical prognosis, including lifespan. The survival motor neuron (SMN1) gene has been shown to be responsible for 99% of SMA cases. An adjacent homologous gene, SMN2, encodes a protein identical to that of SMN1. SMA is caused by a critical reduction in the total amount of functional SMN protein. Typically 80% to 90% of SMN protein is derived from functional SMN1 genes, while 10% to 20% is derived from SMN2 genes. Therefore, SMN protein expression, or dosage, is based largely upon SMN1 gene copy number and, to a much lesser extent, SMN2 gene copy number. Loss of functional production of SMN protein most commonly occurs by deletion of SMN1 and/or SMN2 genes, either by homologous recombination or gene conversion (95% of SMA alleles). The remaining 5% of SMA alleles harbor point mutations in the SMN1 gene(s) that effectively eliminates the production of functional SMN protein from those gene copies. Although a diagnosis of SMA depends upon SMN1 gene copy number, a less severe SMA phenotype may be associated with an increased number (greater than or equal to 3 copies) of functional SMN2 gene copies. Conversely, a severe SMA phenotype may be associated with fewer (less than or equal to 2) functional SMN2 gene copies. | |