The two chapters in this section focus on two fascinating neurodevelopmental disorders – autism and Williams syndrome. Over the past 30 years, these disorders have risen from the obscurity of “undecipherable, enigmatic, rare” disorders to disorders that have and will contribute breakthrough understandings of gene–brain–cognition–behavior relationships. In the process, these disorders also turned out not to be as rare as initially thought.

The advances did not occur all at once, nor did they occur with broad foresight of the significance of these disorders for cognitive neuroscience and the clinical specialties. The advances came slowly in phases reflecting step-wise gains in methodology and technology. The investments supporting this research were meager, reflecting the perceived rarity of and general disinterest in neurodevelopmental disorders. This status did not change until decades of mostly small-sized cognitive studies had identified intriguing features of the cognitive profiles, similarly sized magnetic resonance imaging (MRI) and neuropathologic studies were sufficient to implicate disturbances in pre- and post-natal neuronal organizational and migrational events, and genetic discoveries closed the developmental neurobiologic loop. With the identification of genes came the beginning of the molecular pathophysiologies and the widespread conviction of the significance of these disorders for cognitive neuroscience and behavioral neuropsychiatry. It is now no longer accurate to say that little is known about the cause of autism or Williams syndrome, or that these are minor disorders.