SMA "Silent" Carriers. Why Screen?

Did you know that routine carrier screening for spinal muscular atrophy (SMA) has a false negative rate of 5-8%?

Routine screening merely counts the number of SMN1 copies and does not look to see if they are on different chromosomes. This type of screening provides the total number of SMN1 copies a person has.

Since patients with two copies of SMN1 are typically not deemed carriers, those with two copies of SMN1 on a single chromosome — and none on the other — are missed with this traditional method.

Enhanced SMA carrier screening looks for a SNP to detect these SMA "silent" carriers: those with two copies of SMN1 on a single chromosome.