A group of genetic disorders in which there is an abnormal increase in the size of the body or a body part that is often noted at birth. Examples of overgrowth syndromes include neurofibromatosis, Sotos syndrome, Beckwith-Wiedemann syndrome, Simpson-Golabi-Behmel syndrome, Weaver syndrome, Proteus syndrome, Sturge-Weber syndrome, and fragile X syndrome. Many of these syndromes increase the risk of cancer.