With SCID and SMA being added in many NBS programs world-wide, and XLA being a strong candidate to be added into NBS panels, we developed a multiplex real-time PCR assay to allow the screening of infants with severe forms of PID manifested by T and B cell lymphopenia and identify the absence of exon 7 in the SMN1 gene, which is present in approximately 96% of patients with SMA [16]. The gene discussed is SMN1; the disease is proximal spinal muscular atrophy.