SMA is diagnosed using a molecular blood test, also known as an SMN gene deletion test. This test confirms whether or not an individual has the SMN1 gene mutation that causes SMA. Approximately 95–98% of individuals with a clinical diagnosis of SMA have a mutation in the SMN1 gene.1 This test can also determine the SMN2 gene copy number.

The SMN gene deletion test is performed in pathology labs. It can take anywhere between 3 days to 3 weeks to receive the results. 

Arriving at an SMA diagnosis may take some medical detective work

Because the signs and symptoms of SMA are not highly specific and may occur at different ages and with different severity, an initial diagnosis can be delayed. To help narrow down the diagnosis, healthcare providers may use other diagnostic tests to rule out other forms of muscle disease. These include:

  • additional genetic testing
  • electromyography (a diagnostic technique that measures electrical activity in the muscle) 
  • blood test to measure creatine kinase (an enzyme that leaks out of deteriorating muscles).

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1. Darras B. Pediatr Clin N Am. 2015;62:743–66.