SMN1 and proximal spinal muscular atrophy: In this context, an apparently asymptomatic newborn with a single copy of SMN1 tested positive for a c.223G>A (p.Ala75Thr) variant by an external laboratory; however, the laboratory could not localize the variant to SMN1 or SMN2. Using the assay described here, our laboratory definitively localized the c.223G>A (p.Ala75Thr) variant to SMN2. This result further illustrates the utility of this clinical assay in that the possibility of a SMA diagnosis was drastically reduced for this patient.