Opitz G/BBB syndrome
Also known as: G syndrome; Hypertelorism-Hypospadias syndrome; Opitz-Frias syndrome
Professor John Opitz, an eminent North American geneticist, and colleagues first drew attention to these conditions in 1969 and subsequently. Professor Opitz did not wish to follow the practice of naming syndromes after the medical authors who report the condition, so he suggested conditions are represented by the initials of the names of families who first present. However, with an increasing number of newly reported syndromes, this system fell out of favour.
Medical text written October 2001 by Dr J Tolmie. Last updated September 2007 by Dr J Tolmie, Consultant Clinical Geneticist, Ferguson-Smith Centre for Clinical Genetics, Glasgow, UK.
In Opitz G/BBB syndrome the clinical features mainly affect midline structures of the body. Increased spacing between the eyes (hypertelorism) is often apparent but this is less important than difficulties in swallowing or breathing due to malformation of the larynx (voicebox), trachea (the main airway), or oesophagus (the gullet), or bottom (imperforate anus). Kidney abnormalities (Kidney disease) and hypospadias (displacement of the orifice at the tip of the penis) are common. Other complications are present less frequently.
It is now generally agreed that Opitz G/BBB syndromes are clinically indistinguishable, but it is likely that, in different families, the condition may arise from different genetic changes. This phenomenon is termed genetic heterogeneity and it is important for families because it complicates genetic risk prediction and makes gene testing more difficult.
Probably, there is an Opitz G/BBB gene fault or mutation located on chromosome 22. In a few cases only, a larger chromosome 22q11 deletion has been diagnosed by a special (FISH) chromosome test.
In yet other families, the Opitz G/BBB syndrome gene is located at the tip of the X chromosome in a gene called midline (MID1).
Note that the Opitz G/BBB syndrome is different from another X chromosome condition called Opitz-Kaveggia/FG syndrome, which is sometimes caused by a change in the MED12 gene.
Diagnosis of Opitz-Kaveggia/FG syndrome is usually made by observation of affected individuals with clinical features of the disorder, and its inheritance in an X-chromosome linked fashion within the family lends further support. Affected families should be offered genetic counselling.
Multidisciplinary treatments and support are required for the child who has complex or severe learning disabilities and surgical treatment is required to correct an imperforate or narrowed anus.
This may be very difficult to assess, especially if only one person in a family is affected. Specialist genetic counselling is advisable. Without evidence from the family tree, it might be difficult to estimate the risk of recurrence of the syndrome in a family. Parents and other close relatives may need to be examined for minor features of the syndrome. Rarely, the family tree indicates clear-cut autosomal dominant or X-chromosome linked inheritance that carries high risk of recurrence.
Gene tests are not routinely available but in some families a causative gene change is identified that does permit prenatal testing after chorion villus sampling or amniocentesis. In other families, prenatal diagnosis by ultrasound examination may demonstrate a rare complication associated with the presence of the syndrome in the fetus.
Information and support in the UK for the form of Opitz G/BBB resulting from a chromosome 22q11 deletion is provided by Max Appeal and the 22 Crew (see entry 22q11 Deletion syndromes).
Families can use Contact’s freephone helpline for advice, information and, where possible, links to other families. To meet other families with disabled children, join Contact’s closed (private) Facebook group.