NORD gratefully acknowledges NORD gratefully acknowledges Laura M. Davids, MMSc, NORD Editorial Intern from the Emory University Genetic Counseling Training Program and Cecelia A. Bellcross, PhD, MS, CGC, Associate Professor, Director, Genetic Counseling Training Program, Emory University School of Medicine, for assistance in the preparation of this report.
Simpson-Golabi-Behmel syndrome (SGBS) is a rare genetic condition that mostly affects males. In SGBS type 1, one of the main features is overgrowth, which is when an individual is larger than expected. This can be seen in overgrowth before birth, where the unborn baby is unusually large, and in overgrowth after birth, where a baby is unusually large. Other physical features that are commonly seen in individuals with SGBS are specific facial features like large forehead, nose, lips, and tongue. Some people with SGBS have an opening in the roof of their mouth (cleft palate). They can also have an opening in the upper lip (cleft lip). People with SGBS can have differences in other parts of their bodies too. Some of the differences that are more commonly seen include having an extra nipple, problems with their bones, and a bulge near the belly button called an umbilical hernia. Having SGBS can also mean that a person has a higher chance of having a heart problem. People with SGBS normally have some of these features, but not all of them. People with SGBS have differences and similarities, and some people have a more serious version of the condition than others. Some people with SBGS have intellectual disability, with a wide range of severity. About 10% of people with SGBS develop specific types of tumors as children. SGBS type 2 is the more serious form of the condition, and it can be life threatening in babies who are affected. Although there is no specific treatment or cure, there are ways to manage the symptoms, or specific features a person has. A team of doctors and other health care providers is often needed to determine the treatment options based on each person’s symptoms.
There are many different names for Simpson-Golabi-Behmel syndrome. Some of these names have words that relate to symptoms of the condition and some contain names of doctors who have worked with patients with this condition. The name that is currently the most commonly used is Simpson-Golabi-Behmel syndrome, which combines the names of three doctors. Dr. Simpson published a paper on the condition in 1975, and Dr. Golabi and Dr. Behmel published papers on the condition in 1984.
Simpson-Golabi-Behmel Syndrome Type 1
Many different parts of the body can be affected when a person has SGBS. Not every person with SGBS has the same symptoms, and none have all of these symptoms.
Central Nervous System
Speech and Language
Simpson-Golabi-Behmel Syndrome Type 2
SGBS type 2 is more serious and rarer than type 1. Boys with SGBS type 2 usually die a few months after birth. Most affected boys are born with extra fluid in multiple parts of the body (hydrops fetalis) and they also can have problems with their bones, distinct facial features, issues with organs and other medical problems.
SGBS type 1 is caused by harmful changes (mutations) in the genes GPC3 and GPC4, located on the X chromosome. SGBS type 2 is caused by mutations in the genes OFD1 and PIGA, also located on the X chromosome. They are genetic disorders that are inherited in a recessive X-linked pattern.
The gene glypican 3 (GPC3) contributes to the control of growth and changes in this gene may lead to overgrowth. It is thought that organs of the body such as the heart and liver reach normal size when the GPC3 protein is available in large enough quantities. Concentration is sufficient when GPC3, the growth inhibiting factor, balances the growth promoting factors, such as insulin-like growth factor 2, IGF2.
SGBS is inherited in an X-linked pattern. X-linked genetic disorders are conditions caused by a mutation in a gene on the X chromosome. Mutations are changes in the way that genes, the body’s instructions, are written that cause the genes to not work in the way they should. Females have two X chromosomes but one of the X chromosomes is “turned off” and all of the genes on that chromosome are inactivated. Females who have a disease gene present on one of their X chromosomes are carriers for that disorder. Carrier females usually do not display symptoms of the disorder because it is usually the X chromosome with the abnormal gene that is “turned off”. Some female carriers of SGBS have symptoms, but if they do their symptoms are normally mild. A male has one X chromosome and if he inherits an X chromosome that contains a disease gene, he will develop the disease. Males with X-linked disorders pass the disease gene to all of their daughters, who will be carriers. A male cannot pass an X-linked gene to his sons because males always pass their Y chromosome instead of their X chromosome to male offspring. Female carriers of an X-linked disorder have a 25% chance with each pregnancy to have a carrier daughter like themselves, a 25% chance to have a non-carrier daughter, a 25% chance to have a son affected with the disease, and a 25% chance to have an unaffected son.
SGBS is present from birth (congenital) and can be diagnosed in a baby, even though some of the features might not appear until a child is older. All males who have a mutation in one of the genes for SGBS will have the condition. It is not known what percentage of carrier females have symptoms. As of 2014, there were 250 known cases of SGBS type 1. As of 2019, there have been 8 symptomatic female carriers reported.
Diagnosis of SGBS type 1 is made based on physical features of the patient, family history and genetic testing. There are no official criteria that are used to diagnose the condition. The main physical features are the different types of overgrowth (large body, large head, large fetus, large baby), the specific facial features, abnormalities that happen in the middle of the body (midline defects), and risk for tumors. The other physical features that are considered are organs larger than expected (organomegaly), issues with the skeleton, and problems with the heart, central nervous system, kidney, and gastrointestinal tract that are present from birth. A family history showing an X-linked pattern of inheritance can help with diagnosis. Genetic testing can involve sequencing and deletion/duplication analysis of the GPC3 gene, a chromosomal microarray, or a multigene panel that includes GPC3, GPC4, and other genes related to differential diagnoses.
Patients with SGBS type 1 need to be screened regularly for tumors. Screening should be done every three months until they are four years old. From ages four to seven years old, screening should be done every four months. After age seven, screening should be done every 6 months. Screening should include abdominal ultrasounds, blood tests, urine tests, and chest x-rays.
The treatment for SGBS is based on the type of symptoms that each individual patient has. In the newborn period, right after birth, the baby’s blood sugar levels should be monitored to make sure they are not too low (hypoglycemia). The baby should also be checked to see if they are having problems breathing (airway obstruction). If the baby has any problems with their kidneys (renal anomalies) then their kidney function should also be monitored. Physical examinations should be done to check for a sideways curvature of the spine (scoliosis) during periods of time when the child is growing quickly. Social and intellectual development should also be monitored routinely.
Individuals with cleft palate require the coordinated efforts of a team of specialists. Pediatricians, dental specialists, surgeons, speech therapist, and psychologists must systematically and comprehensively plan treatment and rehabilitation. The palate may be repaired surgically or covered by an artificial device that closes or blocks the opening. Speech and language development need to be assisted by a speech therapist during the preschool years.
For a complete list of different specialists to see based on the specific concern, reference the GeneReviews (listed under Internet sources) for Simpson-Golabi-Behmel Syndrome Type I.
Genetic counseling is recommended for patients and their families
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