C9orf72 and amyotrophic lateral sclerosis: Similarly, the authors reported correction of C9orf72 promoter methylation as well as reduced excitotoxicity, which is typical for ALS motor neurons.51, 52, 53 Recently, two groups used an HDR-based approach to introduce a donor template containing a normal number of repeats in C9orf72 in ALS iPSCs (Figure 1H).54