Introduction to 22q11.2 Deletion Syndrome
What is 22q11.2 deletion syndrome?
22q11.2 deletion syndrome is a genetic disorder. In this syndrome, a tiny piece of chromosome 22 is missing. This can cause many medical problems. These problems may range from heart defects and developmental delays to seizures and effects on facial appearance. These might include cleft palate (an opening in the roof of the mouth).
In 22q11.2 deletion syndrome, a tiny piece of chromosome 22 is missing from the long arm of chromosome 22, at a location called q11.2.
Most people affected by the syndrome do not experience all the health problems that are associated with it. In general, health problems that are present due to 22q11.2 deletion syndrome can be managed with treatment, especially if they are detected early.
In the mid-1960s, an endocrinologist named Dr. Angelo DiGeorge recognized that a particular group of clinical features frequently occurred together, including the following:
- Hypoparathyroidism (underactive parathyroid gland), which results in hypocalcemia (low blood calcium levels)
- Hypoplastic (underdeveloped) thymus or absent thymus, which results in problems with the immune system
- Conotruncal heart defects (such as tetralogy of Fallot, interrupted aortic arch, ventricular septal defects, vascular rings)
- Cleft lip and/or palate
The signs and symptoms of 22q11.2 deletion syndrome can vary from one affected person to another. For that reason, several disorders and collections of symptoms caused by this syndrome have had other names in the past. These names, some of which are still used occasionally, include:
- DiGeorge syndrome
- Velocardiofacial syndrome (VCFS)
- Shprintzen syndrome
- Conotruncal anomaly face syndrome (CTAF)
- Sedlackova syndrome
In addition, some children with the syndrome were previously diagnosed with Opitz G/BBB syndrome or Cayler cardiofacial syndrome. Doctors now understand that these disorders all share the same genetic cause as 22q11.2 deletion syndrome.
Who is affected by 22q11.2 deletion syndrome?
About one in 4,000 people have 22q11.2 deletion syndrome. Some medical experts believe this number to be higher; some people with the chromosome defect have less severe symptoms that may not be diagnosed as 22q11.2 deletion syndrome. Thus, they are unaware they have the syndrome.
What causes 22q11.2 deletion syndrome?
Most people with 22q11.2 deletion syndrome are missing about 30 to 40 genes. The exact function of many of these genes remains a mystery. But one gene, TBX1, probably accounts for the syndrome's most common physical symptoms. These include heart problems and cleft palate. Another nearby gene, called COMT, may also help explain the increased risk for behavior problems and mental illness in people with the syndrome.
About 90 percent of 22q11.2 deletion syndrome cases occur randomly at fertilization or early in fetal development. So most people affected with the disorder have no previous family history of it. However, they may pass the condition on to their children. The remaining 10 percent of cases are inherited from either the mother or the father. When the condition is inherited, other family members could also be affected. Because a person who has this chromosome deletion has a 50 percent chance of passing the deletion to a child, both parents are generally offered the opportunity to have their blood studied to look for the deletion.
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