Confirming a Diagnosis
If a doctor thinks a child or adult has symptoms that suggest they may have SMA, they will arrange for a blood sample to be taken and sent for the SMN1 gene deletion test. If the test shows that both copies of the SMN1 gene have the deletion fault, a diagnosis of 5q SMA will be given. It is now recommended that the number of SMN2 copies is also counted as this can be a helpful indicator of how the condition will affect them in the future (their prognosis), which will in turn guide best care and management. This is also helpful as clinical trials of new treatments often have entry criteria that specify the number of SMN2 copies someone must have to take part.
If the test comes back and only one copy of the SMN1 gene appears to have a fault but the symptoms still suggest SMA, further in-depth genetic testing is recommended via a process called SMN1 gene sequencing. This looks for single, subtle mutations in the gene which if found, confirm a diagnosis of 5q SMA. If both copies of SMN1 are present and not faulty it is very unlikely that SMA is causing the symptoms. Other tests will be needed to make a diagnosis.
Other tests, such as surgically taking a small sample of muscle (muscle biopsy) and tests of nerve function, are not needed to diagnose 5q SMA. However, further tests may be needed for those with later onset SMA as symptoms may be subtler and more difficult to diagnose. For example, a blood test which looks at muscle enzyme (creatine kinase or CK) may be done.