To understand the importance of UNC13A synaptic function on SMA pathophysiology, we investigated the role of SMN in axonal translocation and translation of UNC13A in human induced pluripotent stem cell-derived (hiPSC) motoneurons from two type I and one type II SMA patients (Supplementary Fig. 8a–c). Here, SMN1 is linked to proximal spinal muscular atrophy.