SMN1 and spinal muscular atrophy: In the instance of the genetic disorder spinal muscular atrophy (SMA), A1-mediated suppression of splicing prevents complementation of defective SMN1 (survival motor neuron 1) by an alternative splice isoform of SMN2 [106,107,108]; a therapy targeting this splicing mechanism was recently approved, but viral gene therapy providing intact SMN1 has superseded this approach [109].