SMN1 and spinal muscular atrophy: This is no new concept, because a large and growing number of variants located in protein coding exons have primary disease-causing effects by disrupting splicing—For example, Spinal Muscular Atrophy (SMA) is caused by the loss of SMN1 genes and the C to T substitution in exon 7 of the SMN2 gene that promotes exon skipping in SMN2 and could not compensate the loss of SMN1 [51].