Neurodevelopmental disorders are a major and growing public health challenge. Uniformly, the unmet need is for a human-based approach to investigating the causes, consequences and ultimately treatment of these diseases. A major hurdle in discovering new brain medicines is due to the inability to take biopsies and thus study living brain tissue, as well as limitations of current animal models. Hence, the need is to use living human brain cells to study the functional effects of disease. To this end, I will present new findings from human pluripotent stem cells generated from individuals affected by Fragile X Syndrome (FXS), the leading genetic cause of autism spectrum disorders and intellectual disability.