SMN1 and proximal spinal muscular atrophy: The disease is caused by bi-allelic pathogenic variants in the survival of motor neuron 1 gene (SMN1), resulting in the absence of SMN protein production.1-3,6 The complete absence of this protein would be lethal during the embryonic period, however, the presence of the SMN2 gene, a paralogous gene that varies in copy number, allows for the production of a small amount of functional SMN protein.1-3 The severity of SMA exhibits significant variation, and its clinical manifestations can be classified into five sub-types.1 Type 0 is the most severe form, occurring in the neonatal period.