At early time points in culture, motor neurons derived from SOD1-ALS, C9ORF72-ALS and FUS-ALS patients showed hyperexcitability (Wainger et al., 2014), whereas a separate study showed motor neurons derived from C9ORF72-ALS patients exhibited hypoexcitability at a later time point in culture (Sareen et al., 2013). Here, SOD1 is linked to amyotrophic lateral sclerosis.