SMN2 and spinal muscular atrophy, type 1: For instance, while 90% of individuals with SMA and two copies of SMN2 exon 7 typically have SMA type 1, individuals with SMA that have two copies of SMN2 exon 7 and the c.859G>C variant typically have SMA type 2 or type 3, with no known cases of SMA type 1 in individuals where this variant is present [13,14,33].