Spinal muscular atrophy is caused by the mutation in SMN1 (survival motor neuron 1)gene. SMN 1 gene produces SMN protein. This protein is ubiquitously found in all cells (located in both the cytoplasm and in the nucleus).
The main function that is found to be associated with them are-
Components of spliceosome, involved in pre-m-RNA splicing (transcription) 
Involved in  actin cytoskeletal dynamics (motor axon pathfinding)
Involved in maintaining structural and physiological integrity of neuromuscular junction
Spinal muscular atrophy molecular biology
Spinal muscular atrophy genetics
Duchenne muscular dystrophy laboratory findings
Friedreich's ataxia electrocardiogram
Duchenne muscular dystrophy electrocardiogram
Duchenne muscular dystrophy MRI
Spinal muscular atrophy epidemiology and demographics
Bannayan-Riley-Ruvalcaba syndrome classification