Neurodevelopmental disorders, especially intellectual disability, and the psychiatric disorders autism, and attention-deficit/hyperactivity disorder (ADHD) are major causes of lifelong, chronic impairment. The etiology of these disorders is complex, and hardly understood. No effective treatments are available for autism and intellectual disability, and none of the neurodevelopmental disorders can be cured. We aim to improve the insight into the causes and mechanisms underlying intellectual disability, autism, and ADHD, with the goal of improving the care for our patients, through the development of better diagnostics as well as improved and personalized treatment strategies.