NF1 and neurofibroma: Since neuronal trophic factors that mediate plexiform neurofibroma preneoplastic cell (NF1−/− Schwann cells; shNF1 SCs, Supplementary Fig. 1A) growth have not yet been identified, we leveraged hiPSC-derived sensory neurons that harbor heterozygous NF1 mutations found in patients with (c.1149 C  >  A, p.Cys381X; c.2041 C  >  T, pArg681X; c.6619 C  >  T, p.Gln2207X; Group 1) or without (c.5425 C  >  T; p.Arg1809Cys; Group 2) neurofibromas (Fig. 5E and Supplementary Fig. 5B, C).