Simpson-Golabi-Behmel Syndrome

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.

Genetic Mutations: Simpson-Golabi-Behmel syndrome is caused by genetic mutations, also known as pathogenic variants. Genetic mutations can be hereditary, when parents pass them down to their children, or they may occur randomly when cells are dividing. Genetic mutations may also result from contracted viruses, environmental factors, such as UV radiation from sunlight exposure, or a combination of any of these.

If you suspect you may have this disease, you may want to start collecting your family health history. Information such as other family members who have had similar symptoms, when their/your symptoms first appeared, or exposures to any potential disease-causing environmental factors should be discussed with your medical team.

Known Genetic Mutations: Simpson-Golabi-Behmel syndrome is caused by genetic mutations in the following known gene(s):

GPC3

Given these known genetic mutation(s), you may want to ask your health care team if genetic testing is right for you. Genetic tests are laboratory tests that use samples of blood, saliva, or other tissues to help identify changes in genes, chromosomes, or proteins. Genetic testing can help confirm or rule out a suspected genetic disease, or can provide other useful information to your health care team.

Yes. It is possible for a biological parent to pass down genetic mutations that cause or increase the chances of getting this disease to their child. This is known as inheritance. Knowing whether other family members have previously had this disease, also known as family health history, can be very important information for your medical team.

There are multiple ways, or patterns, a disease can be inherited depending on the gene(s) involved. Based on GARD’s current data, this disease can be inherited in the following pattern(s):

X-Linked: X-linked inheritance means the genetic mutation is located on the X chromosome, one of the sex chromosomes. The male sex chromosome pair consists of one X and one Y chromosome (XY). The female sex chromosome pair consists of two X chromosomes (XX). Because males have just one X chromosome, it takes only one copy of the mutated gene to cause the disease. Females that have one copy of the mutated gene may have symptoms similar to those experienced by affected males, but usually have less severe symptoms, or no symptoms at all.

Female parents with one X-linked mutated gene have a 50% chance of passing on the mutation to each of their biological children. Male parents with an X-linked mutated gene will pass on the mutation to all their female children but cannot pass the mutation on to their male children.