Test Summary

Carrier screening for Spinal Muscular Atrophy (SMA). SMA is one of the most common autosomal recessive diseases, characterized by the degeneration of the anterior horn cells of the spinal cord which leads to symmetric proximal muscle weakness. 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. Although a diagnosis of SMA depends upon SMN1 gene copy number, a less severe SMA phenotype may be associated with an increased number of functional SMN2 gene copies. 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 SMN1 copy number is equal to two. This test will also assess the SMN2 copy number when SMN1 copy number is equal to zero or one, or when it is equal to two in the presence of the g.27134T>G variant.

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