SMN1 and proximal spinal muscular atrophy: Spinal muscular atrophy is an autosomal recessive neurological disorder in children (Feldkotter et al., 2002) that is caused by homozygous loss of the survival motor neuron 1 (SMN1) gene with the retention of the hypomorphic SMN2 gene leading to reduced levels of the ubiquitously expressed SMN protein (Tisdale and Pellizzoni, 2015; Wirth, 2021).