SMN1 and proximal spinal muscular atrophy: Clinically, SMA is characterised by progressive weakness and muscle wasting, ultimately resulting in tetraparesis and difficulties in swallowing and breathing.2, 3, 4, 5 The severity of SMA is influenced by the copy number of the paralogous SMN2 gene, which produces a truncated SMN protein due to skipping of exon 7, with only a small proportion of functional SMN protein generated by each SMN2 copy.