title: Nonsense-mediated messenger RNA decay of survival motor neuron 1 causes spinal muscular atrophy.
abstract: Autosomal recessive proximal spinal muscular atrophy (SMA) is a neurodegenerative disorder resulting from functional loss of survival motor neuron 1 (SMN1). Homozygous absence of SMN1 due to deletion or gene conversion accounts for about 96% of SMA cases. In the remaining 4%, subtle SMN1 mutations are commonly identified. Here, we describe two novel intragenic SMN1 mutations in three type I SMA individuals: a point mutation in exon 3 (c.469C > T) and a substitution in intron 4 (c.628-140A > G). In-vivo splicing assays demonstrated that the intronic substitution creates a novel splice donor site, culminating in aberrant splicing and insertion of 65 bp from intron 4 between exons 4 and 5 in SMN1 transcripts (c.627_628ins65). Both mutations render SMN1 transcripts susceptible to nonsense-mediated mRNA decay (NMD), resulting in mRNA degradation, insufficient SMN protein levels and development of an SMA phenotype. Treatment of patient cell lines with the translation inhibitors puromycin and emetine markedly increased the levels of mutant SMN1 transcripts. A similar effect was observed after siRNA-mediated knockdown of UPF1, a factor essential for NMD. This study provides first evidence that NMD of SMN1 transcripts is responsible for the molecular basis of disease in a subset of SMA patients.
authors.affiliation: Institute of Human Genetics, and Center for Molecular Medicine Cologne, University of Cologne, Kerpener Str. 34, 50931, Cologne, Germany.
authors.forename: Lars
authors.initials: L
authors.lastname: Brichta
authors.forename: Lutz
authors.initials: L
authors.lastname: Garbes
authors.forename: Maria
authors.initials: M
authors.lastname: Jedrzejowska
authors.forename: Sushma-Nagaraja
authors.initials: SN
authors.lastname: Grellscheid
authors.forename: Irmgard
authors.initials: I
authors.lastname: Holker
authors.forename: Katharina
authors.initials: K
authors.lastname: Zimmermann
authors.forename: Brunhilde
authors.initials: B
authors.lastname: Wirth
mesh_terms: D015153:Blotting, Western; D002478:Cells, Cultured / Q000187:drug effects; D018389:Codon, Nonsense / Q000235:genetics*; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics*; D004252:DNA Mutational Analysis; D004640:Emetine / Q000494:pharmacology; D005091:Exons / Q000235:genetics; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D006239:Haplotypes / Q000235:genetics; D006801:Humans; D007438:Introns / Q000235:genetics; D008214:Lymphocytes / Q000378:metabolism / Q000473:pathology; D009134:Muscular Atrophy, Spinal / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D009419:Nerve Tissue Proteins / Q000235:genetics*; D010957:Plasmids; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011691:Puromycin / Q000494:pharmacology; D020365:RNA Helicases; D012326:RNA Splicing; D020871:RNA Stability / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D016601:RNA-Binding Proteins / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055532:SMN Complex Proteins; D055533:Survival of Motor Neuron 1 Protein; D015534:Trans-Activators / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D018389:Codon, Nonsense; D017362:Cyclic AMP Response Element-Binding Protein; D009419:Nerve Tissue Proteins; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; C526471:SMN1 protein, human; D055533:Survival of Motor Neuron 1 Protein; D015534:Trans-Activators; D011691:Puromycin; D020365:RNA Helicases; C101828:UPF1 protein, human; D004640:Emetine