Childhood disintegrative disorder (CDD), the rarest autism spectrum disorder, is defined by a severe, irreversible regression to autism and intellectual disability in children who were developing normally for the first three or more years of their lives. Very little is known about CDD, in part because of its rarity, but given its position at the convergence of autism, intellectual disability and regression, research on CDD may shed light on these important areas of inquiry. Kevin Pelphrey and his team at Yale University are conducting a multifaceted research effort to uncover the etiology of CDD. This effort includes brain imaging studies designed to test whether the social brain of people with CDD is developmentally distinguishable from those with non-regressive forms of autism or other forms of regressive autism. To explore this question further, they also plan to use diffusion tensor imaging to look at the structural connectivity between social brain regions. Finally, they aim to use whole-genome sequencing on all CDD subjects and their parents to identify genetic mutations that may contribute to the disease. Pelphrey's team hopes to link these genetic findings back to the behavioral and brain imaging data. This research represents an intense effort on the levels of behavior, brain and biology to generate a full picture of a devastating form of autism.