LSM2 and proximal spinal muscular atrophy: Importantly, mutations affecting the survival motor neuron (SMN) protein have been linked with a neuromuscular disorder, spinal muscular atrophy (SMA), which has been linked with disruption of snRNP complex assembly (Melki et al., 1994; Lefebvre et al., 1995; Lefebvre et al., 1997; Burlet et al., 1998; Pellizzoni et al., 2002).