SMN Deficiency in SMA: Splicing Gone Awry

Spinal muscular atrophy (SMA) is the most common motor neuron degenerative disease and is the principal genetic cause of infant mortality, affecting 1 in every 6000 newborns. The survival of motor neurons (SMN) gene has been implicated as the disease-causing gene in SMA, and it is deleted or mutated in over 98% of SMA patients. Our lab has pioneered research elucidating the functions of the SMN protein, which we have determined is a part of a large multi-protein complex (the SMN complex) that contains at least seven additional proteins, identified as Gemins 2-7. The SMN complex is essential for the biogenesis of small nuclear RNA ribonucleoproteins (snRNPs), which are the major components of pre-mRNA splicing machinery. We have determined that the genetic aberrations observed in SMA patients result in the depletion of functional SMN within cells. Reduced levels of SMN correspond with a decreased capacity for snRNP assembly and widespread defects in splicing. However, the mechanism by which SMN deficiency and universal defects in splicing lead to the cell-specific phenotype within motor neurons remains unclear. Further research into the role of SMN in spinal muscular atrophy will potentially aid in the development of treatments for this devastating neurodegenerative disease.