MDM4 and proximal spinal muscular atrophy: However, despite rescuing the reduction of MN numbers seen in SMA mice, neither the inhibition of p53 signaling nor virus-mediated overexpression of full-length Mdm2 and Mdm4 is able to rescue vGlut1+-synapse loss (Simon et al., 2017; Van Alstyne et al., 2018).