SMN1 and proximal spinal muscular atrophy: 2015; Butchbach.2021). For genotype–phenotype correlation studies among SMA patients, it is necessary to first identify whether they carry compound heterozygous mutations or if they are SMN1 -unlinked SMA. Subsequently, subtle mutation(s) should be identified in cases of heterozygousity (Allison et al. 2022) have reported that some of the subtle mutations result in severe phenotypes, while others might be considered as mild mutations according to their effect on the expressed SMN protein.