Spinal muscular atrophy (SMA) is one of the most common lethal recessive genetic conditions, with an incidence of 1 in 10,000 births. The condition is associated with significant motor disability, respiratory and nutritional compromise, and death in infancy or childhood in more than 50% of affected children. Epidemiological data indicates that symptom onset before 18 months of age occurs in more than 80% of affected children. There is significant neuronal loss within the first six months in infants with SMA type I, the most severe form of SMA. The majority of undiagnosed affected infants who present in their first 12 months have medical crisis with acute respiratory failure. By the time a diagnosis is made, these infants are often severely nutritionally compromised, potentially exacerbating irreversible loss of neurological function and the resulting compromised respiratory reserve. There have been considerable advances toward the development of new therapies for SMA. The recently US FDA approved new treatment for SMA has led
to increased interest in newborn screening (NBS) in public health contexts. SMA detection can be multiplexed, at minimal additional cost, with existing screening assays used to identify severe combined immunodeficiency (SCID) infants.
Here we report a real-time PCR assay to simultaneously measure copy numbers of three different DNA segments using DNA extracted from a single 3.2mm punch of a dried blood spot. The PCR assay identifies the absence of exon 7 in the SMN1 gene while simultaneously evaluating the copy number of the T-cell receptor excision circles (TREC). Additionally, the amplification of a reference gene, RPP30, was included in the assay as a quality/quantity indicator of DNA isolated from the dried blood NBS specimens.