We provide evidence that motor neurons from SMA patients display reduced expression of proteins involved in developmental and differentiation pathways, including ubiquitin-activating enzyme 1 (UBA1) and ubiquitin carboxyl-terminal esterase L1 (UCHL1), and that most of these changes are distinct from those seen in the fibroblast cell lines from which the iPSCs were derived. Here, UBA1 is linked to proximal spinal muscular atrophy.