Spinal Muscular Atrophy (SMA) Carrier Screen

Formal Name of the Test:
Spinal Muscular Atrophy (SMA) Carrier Screen

Other Names Used:
SMA Silent Carrier, SMN2 Copy Number, SMN Deletions, SMN1 Copy Number, 2+0 Silent Carrier

Sample Required:
Whole blood

Test Overview:
Spinal Muscular Atrophy (SMA) is one of the most common autosomal recessive diseases, characterized by degeneration of the spinal cord’s anterior horn cells, resulting in symmetric proximal muscle weakness. The survival motor neuron (SMN1) gene has been linked to 99 percent of SMA cases. SMN2, an adjacent homologous gene, encodes a protein that is identical to SMN1. SMA is caused by a significant decrease in the total amount of functional SMN protein in the body. Although the SMN1 gene copy number is required for SMA diagnosis, a less severe SMA phenotype may be associated with an increased number of functional SMN2 gene copies. When the SMN1 copy number is equal to two, this test is appropriate to determine the SMN1 copy number and to refine the risk that the patient is a silent carrier (also known as 2+0 carrier) by determining the presence or absence of the g.27134T>G variant. When the SMN1 copy number is zero or one, or two in the presence of the g.27134T>G variant, this test will also assess the SMN2 copy number.

Test Preparation:
There is no need for any prior preparation.

Test Performed at:
Quest Diagnostics, Test Code 39445 

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