Over the last four decades, breakthroughs in genetic knowledge, together with the emergence of disciplines devoted to the scientific study of developmental disorders have resulted in much greater awareness of the many different behavioural and genetic phenotypes involved. It is now evident that not only do different disorders have different causes and different manifestations, but different neurological and biochemical bases, different responses to intervention, and different life courses. Reflecting the enormous changes that have taken place in our knowledge and understanding of...