There are now several diseases known to be caused by aberrant expression of splicing factors, for example, spinal muscular atrophy (loss of SMN), amyotrophic lateral sclerosis (mutants of FUS) and retinitis pigmentosa (loss of constitutive splicing factors PRP8 and PRP18 (40). The gene discussed is PRPF18; the disease is spinal muscular atrophy.