The SHEF4 line (male, UK Stem Cell Bank), referred to as the “ES line”, was obtained under full Ethical/Institutional Review Board approval of the University of Edinburgh. Written informed consent was obtained from each participant providing the lines iPS1 (female), iPS2 (male), iPSC91 (female), and iPSC92 (male). The derivation, characterization, and validation of iPS lines were performed as described previously 18 and are detailed in the Supporting Information Text. For neuralization, spontaneous embryo body formation was induced following cell lifting with dispase (17105‐041, Life Technologies, CA, USA) and collagenase (17104‐019, Life Technologies). Embryo bodies were cultured for 7 days, with dual‐SMAD inhibition 19, and in chemically defined media (CDM) that contained 50% Iscove's modified Dulbecco's medium (Invitrogen, CA, USA, 50% F12, BSA (5 mg/ml, Europa, Cambridge, UK), 1% chemically defined Lipid 100 (Invitrogen), monothioglycerol (450 μM, Sigma‐Aldrich, Gillingham, UK), insulin (7mg/ml), Roche, Basel, Switzerland), transferrin (15 mg/ml, Roche), 1% penicillin/streptomycin), supplemented with N‐acetyl cysteine (1 mM, Sigma), activin Inhibitor (10 μM, R&D Systems, MN, USA), and Dorsomorphin (2 μM, Merck Millipore, Darmstadt, Germany). NPCs were cultured in suspension as neurospheres
