SMN1 and proximal spinal muscular atrophy: In newborn screening programs (NBS) currently testing for SMA, real-time PCR (qPCR) is used as a first-tier method to detect a homozygous deletion of exon 7 in SMN1. Positive NBS results must be confirmed by multiplex ligation-dependent probe amplification (MLPA), which can detect both homozygous and heterozygous deletions.