C9orf72 and amyotrophic lateral sclerosis: Other early events observed by the authors were the loss of synaptic activity in C9orf72-iPSC-derived MNs which could be reflecting a general loss of action potential generation in culture; however, due to the evidence of loss and dysfunction of synapses in ALS [50–55], specific deficits in synaptic transmission might also contribute to reductions in synaptic activity recorded from patient iPSC-derived MNs.