Costello syndrome is a genetic disorder that affects many parts of the body. It includes developmental (neurocognitive) delays and impaired learning, unique facial features that make people with the condition look like they're related to each other, loose folds of extra skin (especially on the hands and feet), and unusually flexible joints. Problems with the heart are common. Although infants with Costello syndrome may be large at birth, they have difficulty feeding and grow more slowly than other infants. Their final height will be shorter than average.
Beginning in early childhood, people with Costello syndrome are at an increased risk of developing certain tumors. These include noncancerous papillomas (small growths that usually develop around the nose and mouth or near the anus), as well as malignant tumors.