Although a significant decline in MNs over time has been reported as a hallmark of SMA patient iPSC-derived MNs (Chang et al., 2011; Corti et al., 2012; Ebert et al., 2009), the two independent SMA-iPSC lines produced and maintained a similar number of HB9-positive MNs compared to control iPSCs after 40 and 50 days of differentiation (Figure 1E). The gene discussed is SMN1; the disease is proximal spinal muscular atrophy.