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DiGeorge Syndrome |
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DiGeorge Syndrome is a disorder caused by the deletion of a small piece of chromosome 22. The deletion occurs near the middle of the chromosome at a location designated q11.2. This condition is also called 22q11.2 deletion syndrome. DiGeorge Syndrome (22q11.2 deletion syndrome) affects an estimated 1 in 4,000 newborns. SymptomsThe features of this syndrome vary widely, even among affected members of the same family, and involve many parts of the body. Characteristic signs and symptoms include heart defects that are often present from birth, an opening in the roof of the mouth (a cleft palate) or other defects in the palate, recurrent infections caused by problems with the immune system, and mild differences in facial features. Affected individuals may also have kidney abnormalities, low levels of calcium in the blood (which can result in seizures), a decrease in blood platelets (thrombocytopenia), significant feeding difficulties, and autoimmune disorders such as rheumatoid arthritis and Graves' disease. Skeletal differences are possible, including abnormalities of the spinal bones (vertebrae), extra fingers or toes (polydactyly), and premature fusion of certain bones of the skull (craniosynostosis). Many children with 22q11.2 deletion syndrome have developmental delays and learning disabilities. Later in life, they are at an increased risk of developing mental illnesses such as schizophrenia, depression, anxiety, and bipolar disorder. Additionally, affected children are probably more likely than children without 22q11.2 deletion syndrome to have developmental disorders (such as autism) that affect communication and social interaction. CausesThe TBX1 and COMT genes are associated with 22q11.2 deletion syndrome. Most people with 22q11.2 deletion syndrome are missing about 3 million base pairs (the building blocks of DNA) on one copy of chromosome 22 in each cell. This region contains about 30 genes, many of which have not been well characterized. A small percentage of affected individuals have shorter deletions in the same region. This condition is often described as a contiguous gene deletion syndrome because a deletion in chromosome 22 leads to the loss of many genes that are close together. Researchers are working to identify all of the genes that contribute to the features of 22q11.2 deletion syndrome. They have determined that the loss of a particular gene on chromosome 22, TBX1, is probably responsible for many of the syndrome's characteristic signs (such as heart defects, a cleft palate, distinctive facial features, and low calcium levels). The loss of another gene, COMT, in the same region of chromosome 22 may help explain the increased risk of behavioral problems and mental illness. Additional genes in the deleted region likely contribute to the varied features of 22q11.2 deletion syndrome. Can 22q11.2 deletion syndrome be inherited? The inheritance of 2q11.2 deletion syndrome appears to be autosomal dominant because a deletion in one copy of chromosome 22 in each cell is sufficient to cause the condition. Most cases of 22q11.2 deletion syndrome are not inherited. The deletion occurs most often as a random event during the formation of reproductive cells (eggs or sperm) or in early fetal development. Affected people typically have no history of the disorder in their family, though they can pass the condition to their children. In fewer than 10 percent of cases, a person with this condition inherits the deletion in chromosome 22 from a parent. In inherited cases, other family members may be affected as well. TreatmentSee GeneTests Web site.
Reference: Genetics Home Reference, U. S. National Library of Medicine
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