Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disorder and is the most common genetic cause of infantile death. The SMA-determining gene is located on chromosome 5q, and is called survival motor neuron-1 (SMN1). Remarkably, a nearly identical copy gene is present called SMN2. This gene has the capacity to encode an identical protein compared to SMN1, however, due to a single silent non-polymorphic nucleotide difference, the majority of SMN2-derived transcripts are alternatively spliced and encode a truncated and biochemically defective protein called SMN?7. To date, SMN2 is the only SMA modifying gene. Milder phenotypes correlate with an increase in the number of SMN2 copies, typically ranging from two to four copies. The genetic context of SMA makes this disease especially amenable to therapeutic intervention including: SMN2 is retained in essentially all SMA patients;SMN2 is ubiquitously expressed in all tissues;and SMN2 retains the capacity to encode a normal, full-length SMN protein. Therefore, SMN2 has been identified as a major target for a potential SMA therapies. The most attractive possibilities include stimulating total SMN2 transcription and/or modulation of the SMN2 alternative splicing event. To take advantage of the unique SMA genetic context, the goal of this application is to develop novel RNAs that modulate SMN2 splicing. Through the use of a viral delivery system (Aim 1), these RNAs will be examined in a variety of experimental contexts designed to identify RNAs that induces the highest level of full-length SMN2 expression (Aim 1 and 2). The top candidate RNAs will then be examined in a murine model of SMA to determine whether the RNAs can modulate SMN2 in an organism and whether this expected increase in full-length SMN2 expression lessens the well described mild SMA phenotype in transgenic mice (Aim 3). While the experiments described in this application have immediate implications for the development of a SMA therapy, the results could be used as a model for a broad range of genetic disorders in which correcting a splicing defect would restore functionality to a disease-causing gene.
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