SMN1 and proximal spinal muscular atrophy: Cell cycling defects have been implicated in several studies in SMA: ASO-induced SMN depletion in adult mice showed that cell signalling pathways were most affected implicating SMN in DNA replication and possibly DNA repair66; brain weight and cell number changes in mouse model of severe SMA indicated a potential role for SMN in proliferation rather than apoptotic cell death67; and Drosophila loss or gain of SMN function disrupts larval growth and germline stem cell proliferation and differentiation68.