is 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. Heart abnormalities are common, including an unusually fast heartbeat (tachycardia), structural heart defects, and a form of heart disease that enlarges and weakens the heart muscle (hypertrophic cardiomyopathy). Beginning in early childhood, people with Costello syndrome are at an increased risk of developing certain cancerous and noncancerous tumors. Costello syndrome is caused by mutations in the HRAS gene. It is considered an autosomal dominant condition, but almost all reported cases have resulted from new gene mutations and have occurred in people with no history of the disorder in their family.
The signs and symptoms of Costello syndrome overlap significantly with those of two other genetic conditions, cardiofaciocutaneous (CFC) syndrome and Noonan syndrome. While the three conditions are distinguished by their genetic cause and specific patterns of signs and symptoms, it can be difficult to tell them apart in infancy. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.