In 1977, Dr. Jack Costello, a geneticist in New Zealand, first identified a genetic disorder, now known as Costello syndrome (CS), characterized by delayed development and intellectual disability, distinctive facial features, loose folds of extra skin (especially on the hands and feet), and unusually flexible joints. This condition is very rare and is estimated to affect 200 to 300 people worldwide.

Children with Costello syndrome are often delayed in reaching developmental milestones, such as speaking, sitting, and walking. Affected individuals may also have intellectual disabilities that can vary in severity.