SMN1 and proximal spinal muscular atrophy: The maturation of snRNPs has been shown to be impaired by a deletion in SMN (Gabanella et al., 2007; Shpargel and Matera, 2005; Wan et al., 2005; Winkler et al., 2005; Zhang et al., 2008), while alterations to pre-mRNA splicing events, proposed to be a downstream consequence of this impairment, have been observed in several models of SMA (Custer et al., 2013; Huo et al., 2014; Zhang et al., 2008).