This day brings awareness to a rare, misdiagnosed syndrome. The genetic syndrome causes a range of physical, cognitive, and medical challenges. Though present from birth, it is not always diagnosed at birth. It is named after Cornelia de Lange, one of the first physicians to observe and document the condition in 1933.

Cornelia de Lange Syndrome Awareness Day is observed on the second Saturday in May.

Founded in 1989, the day serves to educate the general public about this syndrome that affects an estimated 1 in 10,000-30,000.