De Santis et al. (2017) found no significant difference in FUS expression by gene editing with introduction of P525L mutation and wild type FUS iPSC-derived MNs. These results are in contrast to ours but one has to take into account differences in mutations analyzed, methods applied and cell models. There is only one study to our knowledge so far regarding the R521L FUS mutation. Dash et al. (2020) found mutant R521L FUS not to be differentially expressed in iPSC-derived MNs from ALS patients in a microarray based study. Here, FUS is linked to amyotrophic lateral sclerosis.