Different genetic disorders predispose individuals to display specific, etiology-related profiles, personalities, and maladaptive behaviors. Using groups with genetic etiologies as stand-ins or proxies for a specific behavior or set of behaviors, one can then examine how others in the child's environment react and whether such reactions are limited to a particular disorder or occur generally to all individuals showing that behavior. Just as twins, adopted, and institutionalized children have all been used as natural experiments to tell us about typical development, so too can groups with specific genetic syndromes help us to understand the nature and mechanisms of the reactions and behaviors of others.