SMN1 and spinal muscular atrophy: Loss of SMN1 and SMN2 results in embryonic death; mutations in SMN1 are associated with spinal muscular atrophy, mutations in SMN2 do not lead to disease; forms heteromeric complexes with proteins such as SIP1 and GEMIN4, and also interacts with several proteins known to be involved in the biogenesis of snRNPs, such as hnRNP U protein and the small nucleolar RNA binding protein [RefSeq]