FMR1 and proximal spinal muscular atrophy: For example, mutations in FMRP are responsible for Fragile X syndrome (Penagarikano et al. 2007), dysregulation of TDP-43 underlies amyotrophic lateral sclerosis (ALS; Ling et al. 2013; Gao et al. 2019), and mutations in SMN1 cause spinal muscular atrophy (SMA; Farrar and Kiernan 2015).