A leaky splicing mutation affecting SMN1 exon 7 inclusion explains an unexpected mild case of spinal muscular atrophy
✍ Scribed by Myriam Vezain; Bénédicte Gérard; Séverine Drunat; Benoît Funalot; Séverine Fehrenbach; Virginie N'Guyen-Viet; Jean-Michel Vallat; Thierry Frébourg; Mario Tosi; Alexandra Martins; Pascale Saugier-Veber
- Book ID
- 102260665
- Publisher
- John Wiley and Sons
- Year
- 2011
- Tongue
- English
- Weight
- 265 KB
- Volume
- 32
- Category
- Article
- ISSN
- 1059-7794
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✦ Synopsis
Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder resulting, in most cases, from homozygous deletions of the SMN1 gene or, in rare cases, from SMN1 intragenic mutations.
Here we describe the identification and characterization of c.835À3C4T, a novel SMA-causing mutation detected in the intron 6 of the single SMN1 allele of a type IV SMA patient. We demonstrate both ex vivo and in vivo that c.835À3C4T is a deleterious splicing mutation that induces a modest but unequivocal exclusion of exon 7 from the SMN1 transcripts, its ''leakiness'' explaining the exceptionally mild phenotype of this patient. This mutation creates a putative high-affinity binding site for the splicing repressor protein hnRNP A1 overlapping the splice acceptor site of exon 7 (UAG|GGU). Our findings support the current therapeutic strategies aiming at correcting exon 7 splicing in SMA patients, and bring clues about the level of exon 7 inclusion required to achieve a therapeutic effect.