SMN2 and proximal spinal muscular atrophy: The clinical diagnosis of SMA was made in accordance with the first version of the SoC recommendations [16], because the recruitment took place between April 2015 and May 2018: for this reason, the percentiles were divided by SMA1 and SMA2 and not according to the functional classification reported in the 2018 update of the SoC recommendations, which classifies SMA patients as sitters and non-sitters; also, SMN2 copy number was not systematically collected in our study.