Simpson-Golabi-Behmel syndrome (SGBS) is a condition that affects many parts of the body and occurs primarily in males. SGBS is an overgrowth disorder, meaning that people with the disease are larger than average at birth (macrosomia) and continue to grow and gain weight at an unusual rate. The severity varies from very mild forms in carrier females to infantile lethal forms in affected males. The infantile lethal form of SGBS is sometimes known as SGBS type 2. People with SGBS typically have distinctive facial features, including a large distance between the eyes (hypertelorism), an unusually wide mouth (macrostomia) with a large tongue (macroglossia), and abnormalities of the roof of the mouth (palate). Other, findings include extra nipples, various birth defects such as a protrusion of the lining of the abdomen through the area around the belly button (umbilical hernia), and skeletal anomalies. Some people with the condition have a mild to severe intellectual disability. About 10 percent of people with SGBS develop tumors in early childhood, including a rare type of kidney cancer (Wilms tumor) and cancer of the nerve tissue (neuroblastoma). SGBS can be caused by genetic changes in the GPC3 and GPC4 genes. Genetic changes in other genes have been studied, but have in most instances have only been described in one person or one family. In other cases, the cause is unknown. SGBS is inherited in an X-linked manner.