A rare genetic condition makes people warm up to total strangers instantly

Williams syndrome is caused by the deletion of about 25 genes on chromosome 7, and one striking effect is extreme, indiscriminate friendliness: people with the condition show little normal wariness of strangers and often approach anyone eagerly. Researchers sometimes study it as almost a mirror image of autistic social withdrawal, and have traced part of the effect to altered amygdala activity.

— J.C.P. Williams et al., Williams syndrome — Condition first described 1961