X-linked Opitz G/BBB syndrome
NORD is very grateful to Dr. Germana Meroni, PhD, Group leader, Cluster in Biomedicine (CBM), AREA Science Park, Trieste, Italy, for assistance in the preparation of this report.
Synonyms of X-linked Opitz G/BBB syndrome
- hypertelorism-hypospadius syndrome (obsolete)
- Opitz BBBG syndrome
- Opitz-G syndrome
- telecanthus-hypospadius syndrome (obsolete)
- No subdivisions found.
X-linked Opitz G/BBB syndrome is a rare genetic disorder characterized by facial anomalies, respiratory and genitourinary abnormalities and other midline defects as well as developmental delay or mental retardation. There is a wide variation in severity of this condition, even among members of the same family. X-linked Opitz G/BBB syndrome is an X-linked genetic condition associated with alterations (mutations) in the MID1 gene.
X-linked Opitz G/BBB syndrome is a rare genetic disorder mainly characterized by facial anomalies, respiratory and genitourinary abnormalities as well as developmental delay or mental retardation.
Facial anomalies may include widely spaced eyes (hypertelorism), a prominent forehead, widow's peak, broad nasal bridge, nostrils that are tipped forward, and cleft lip/palate.
Respiratory abnormalities can include laryngo-esophageal clefts that result in difficulty swallowing and breathing. Genitourinary problems can include abnormal placement of the urethra in the penis (hypospadias), undescended testes and sometimes kidney abnormalities. Anal defects may also be present and include absent or mis-positioned anal opening. Congenital heart defects such as ventral septal defects and atrial septal defects as well as brain defects such as agenesis or hypoplasia of the brain region that connects the two hemispheres (corpus callosum) and hypoplasia of the cerebellum also in the context of more complex defects such as Dandy-Walker malformation.
There is a wide variation in the presentation of the clinical signs and in the severity of this condition, even among members of the same family.
Approximately 50% of affected males have developmental delay or mental retardation. Carrier females usually have hypertelorism only.
X-linked Opitz G/BBB syndrome is inherited as an X-linked genetic condition. X-linked genetic disorders are conditions caused by an abnormal gene on the X chromosome and occur mostly in males. Males have one X chromosome that is inherited from their mother and if a male inherits an X chromosome that contains a disease gene he will develop the disease. Females that have a disease gene present on one of their X chromosomes are carriers for that disorder. Carrier females usually do not display clinical signs because females have two X chromosomes and one is inactivated so that the genes on that chromosome are nonfunctioning. It is usually the X chromosome with the abnormal gene that is inactivated.
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.
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 to male offspring.
The MID1 gene is the only gene known to be associated with Opitz G/BBB syndrome.
The prevalence of Opitz G/BBB syndrome is estimated to be 1/50,000-1/100,000 males.
Chromosome 22q11.2 deletion syndrome is now known to include the autosomal dominant form of Opitz G/BBB syndrome. Besides a different kind of inheritance, this condition can be distinguished from the X-linked type by chromosome analysis that shows a submicroscopic deletion of chromosome 22. (For more information on this disorder, choose "chromosome 22q11.2 deletion" as your search term in the Rare Disease Database.)
FG syndrome type 1 (FGS1) is an X-linked genetic disorder that is characterized by poor muscle tone (hypotonia), mental retardation, constipation and or anal anomalies and complete or partial absence of the part of the brain that connects the two hemispheres of the brain (corpus callosum). Other features of the disorder are small and simple ears, tall and prominent forehead, wide and flat thumbs and great toes and downslanting eyes. FGS1 is an X-linked genetic disorder caused by a recurrent abnormality (mutation) in the MED12 gene. The spectrum of disorders caused by mutations in this gene is still being defined. (For more information on this disorder, choose "FG" as your search term in the Rare Disease Database.)
Craniofrontonasal dysplasia is a very rare inherited disorder characterized by abnormalities of the head and face (craniofacial area), hands and feet, and certain skeletal bones. Major symptoms of this disorder may include widely spaced eyes (ocular hypertelorism), a groove (cleft) on the tip of the nose, an unusually wide mouth, malformations of the fingers and toes, and/or underdevelopment of portions of the face (midface hypoplasia), such as the forehead, nose, and chin. In addition, the head may have an unusual shape due to premature closure of the fibrous joints (sutures) between certain bones in the skull (coronal synostosis). Craniofrontonasal dysplasia follows X-linked inheritance in most families, but females are more severely affected than males. An autosomal dominant form of the disorder has also been discussed in the medical literature. (For more information on this disorder, choose "craniofrontonasal" as your search term in the Rare Disease Database.)
Mowat-Wilson syndrome (MWS) is a rare genetic disorder that may be apparent at birth or in the first year of life. MWS is characterized by mental retardation, distinctive facial features and seizures. Other congenital anomalies occur in some individuals and can include a gastrointestinal disease known as Hirschsprung disease in which a narrowing of a portion of the colon is present, heart (cardiac) defects, kidney (renal) abnormalities, male genital abnormalities and short stature. Some affected individuals may not be recognized until childhood or adulthood, especially when Hirschsprung disease is not present. Mowat-Wilson syndrome is caused by an abnormality in ZFHX1B gene that is usually the result of a new genetic change (mutation) in the affected person. (For more information on this disorder, choose "Mowat-Wilson" as your search term in the Rare Disease Database.)
The diagnosis of Opitz G/BBB syndrome is usually made by clinical findings. It is not possible to distinguish this condition from chromosome 22q11.2 deletion syndrome (autosomal dominant Opitz G/BBB syndrome) based on physical features alone. Diagnosis of X-linked Opitz Syndrome can be done by way of inheritance and by molecular genetic testing for mutations in the MID1 gene that is available (15%-45% of affected males have been found to have a mutation).
Widely spaced eyes and cleft lip and palate associated with this condition can sometimes be visualized with prenatal ultrasound.
X-linked Opitz G/BBB syndrome is treated by a team of specialists including surgeons, speech therapists, neuropsychologists and early intervention specialists. Regular assessment of hearing is recommended for affected children with cleft lip and palate.
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