SMN1 and neurodegenerative disease: Moreover, the deficiency of SMN causes human neurodegenerative disease spinal muscular atrophy (SMA) (19–21), and knockdown of Gemin2 causes motor neuron degeneration in zebrafish (22) and depresses motoric abilities in Drosophila (23), emphasizing the pathophysiological relevance of the Sm-core assembly pathway.