BD and normal iPSCs were derived from fibroblasts using a Cyto-Tune Sendai reprogramming kit (Invitrogen) according to the manufacturer’s instructions. All iPSCs were characterized as previously described28. iPSC colonies were cultured on Matrigel-coated dishes (BD Biosciences) using mTeSR1 medium (StemCell Technologies). Embryoid bodies were formed by mechanical dissociation of iPSC colonies using collagenase and plating onto low-adherence dishes in DMEM/F12 (Invitrogen) supplemented with N2 and B27. For embryoid body differentiation, floating embryoid bodies were treated with DKK1 (0.5 μg ml−1), SB431542 (10 μm), noggin (0.5 μg ml−1) and cyclopamine (1 μm) for 20 days. To obtain neural progenitor cells, embryoid bodies were plated onto polyornithine/laminin (Sigma)-coated dishes in DMEM/F12 plus N2 and B27. Rosettes were manually collected and dissociated with accutase (Chemicon) after 1 week and plated onto laminin-coated dishes in neural progenitor cell media (DMEM/F12, 1× N2, 1× B27 (Invitrogen), 1 μg ml−1 laminin and 20 ng ml−1 FGF2 (Invitrogen)). To obtain mature neurons, neural progenitor cells were differentiated in DMEM/F12 supplemented with 1× N2, 1× B27, 20 ng ml−1 BDNF (Peprotech), 1 mM dibutyrl-cyclicAMP (Sigma), 200 nM ascorbic
