The SALSA MLPA Probemix P021-B1 version provides accurate copy number determination of the SMN1 and SMN2 genes and the SMN1/2Δ7–8 variant and will likely result in a more clear picture of the functionality of the SMN1/2Δ7–8 variant in the future when more SMA patient samples are analyzed. This evidence concerns the gene SMN1 and proximal spinal muscular atrophy.