Survival motor neuron gene transcript analysis in muscles from spinal muscular atrophy patients.

We have identified and characterized four different mRNA isoforms of the survival motor neuron (SMN) gene from skeletal muscle of 9 SMA patients and 15 unaffected controls. These isoforms appear to be generated by combinatorial splicing of both exons 5 and 7 of the SMN telomeric and centromeric gene copies. The full-size and the truncated SMN-1b isoforms of the telomeric SMN copy are significantly reduced in muscle of SMA patients, irrespective of the disease types. Our results suggest that multiple RNA splicing is operative in the two SMN-related genes and that SMN-related polypeptides may be active in the muscle.