In Spinal Muscular Atrophy, the survival motor neuron 1 gene SMN1 is deleted or inactivated. The nearly identical SMN2 gene has a silent mutation that impairs the utilisation of exon 7 and the production of functional protein. It has been hypothesised that therapies boosting SMN2 exon 7 inclusion might prevent or cure SMA. Exon 7 inclusion can be stimulated in cell culture by oligonucleotides or intracellularly expressed RNAs, but evidence for an in vivo improvement of SMA symptoms is lacking. Here we unambiguously confirm the above hypothesis by showing that a bifunctional U7 snRNA that stimulates exon 7 inclusion, when introduced by germ-line transgenesis, can efficiently complement the most severe mouse SMA model. These results are significant for the development of a somatic SMA therapy, but may also provide new means to study pathophysiological aspects of this devastating disease.

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