This hyper-excitability is consistent with the lancinating pain that patients with HSN1 experience and, indeed, iPSC lines from those patients with higher neuropathic pain inventory (NPSIs) scores, higher Charcot-Marie-Tooth neuropathy scores (CMTNSs), and younger age of pain onset (Figure 1A) were those in which we found hyper-excitability. This evidence concerns the gene SPTLC1 and Charcot-Marie-Tooth disease, axonal, type 2FF.