The SMN1 gene deletion test is recommended as the first diagnostic step for a patient suspected to have SMA.
The deletion status can be tested by using polymerase chain reaction (PCR) to determine if both copies of SMN1 exon 7 are absent, which occurs in 95% of affected individuals. PCR can reliably and accurately measure SMN1 and SMN2 copy numbers over a wide range (i.e. 0–6 copies).1,2
Molecular genetic testing using microbead technology has demonstrated:5
If a patient is found to have a single copy of the SMN1 gene but the clinical presentation is suggestive of SMA, sequencing of the remaining SMN1 gene may identify the mutation and confirm the diagnosis of SMA.
If the individual presenting with symptoms of SMA is shown to have 2 copies of the SMN1 gene, then other motor neuron disorders might be considered in the differential diagnosis.1
Although newborn screening is not yet standard practice, time to diagnosis is critical. Based on the natural history of the disease, earlier diagnosis leading to earlier intervention may help improve outcomes for individuals with SMA.6