3 Diagnostic Tools for Spinal Muscular Atrophy
Often the first sign of spinal muscular atrophy (SMA) is infants failing to meet development milestones such as supporting their heads, rolling, crawling, etc. This is usually highlighted by the parents or primary care doctor during routine assessments. If babies aren’t meeting their milestones then they will undergo various tests to determine what the problem is.
If SMA is suspected, the following tests will be conducted:
In most cases of SMA, both copies of the SMN1 exon 7 are missing, this can usually be detected through a simple blood test and is the most effective and least invasive way of diagnosing the disease. Parents who both carry the faulty SMN1 gene will have a 25 percent chance of passing the mutation on to their child, which causes SMA. The blood test is accurate in approximately 95 percent of cases but it cannot determine whether the SMA is type, 1, 2, or 3–the time of onset and physical symptoms of the patient will usually determine this. Find out more about genetic testing for SMA here.
For the small percentage of patients where SMA is suspected but didn’t show up in the genetic blood test, an electromyography test will be necessary. This is a fairly invasive procedure which may cause pain and discomfort to the patient.
Needle electrodes are used to record muscle activity by stimulating motor neurons which lead to electrical activity within the muscles. The test can also be used to diagnose other neuromuscular diseases such as motor neuron disease. Find out more about electromyography tests here.
In rare cases when genetic or electromyography tests are not successful in delivering a diagnosis, doctors will need to take a biopsy of one of the muscles to determine if the patient has SMA. This involves taking a small piece of muscle, usually from the thigh, and testing it to see if it has the characteristics found in SMA. This test can distinguish between the different types of SMA as muscle fibers in type 1 SMA patients will look different to those of types 2 and 3. Find out more about muscle biopsies here.
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