All genes (TCF4, EHMT1,33SATB2 and MBD5) that we have studied to develop the current model appear to enhance NSC differentiation, suggesting that NSCs may be primed to differentiate too early; however, a ‘positive control' example of an NDD, Fragile X syndrome caused by a trinucleotide repeat expansion and leading to supressed expression of FMR1, shows deficits in differentiation in iPSC-neural stem cell models,73 possibly suggesting Fragile X syndrome is caused by increased proliferation markers and decreased differentiation markers. The gene discussed is FMR1; the disease is fragile X syndrome.