The Genetics

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Genetics

22q11.2 deletion syndrome is inherited in an autosomal dominant pattern.

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, but many of these genes 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.

Researchers have not yet identified all of the genes that contribute to the features of 22q11.2 deletion syndrome. They have determined that the loss of one 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). A loss of this gene does not appear to cause learning disabilities, however. Additional genes in the deleted region are likely to contribute to the signs and symptoms of 22q11.2 deletion syndrome.

The 22q11.2 deletion syndrome can be inherited in an autosomal dominant manner. Almost all (about 93%) of cases have a de novo (new to the family) deletion of 22q11.2 but about 7% inherit the 22q11.2 deletion from a parent. Children of an individual with deletion 22q11.2 have a 50% chance of inheriting the 22q11.2 deletion. Prenatal testing, such as amniocentesis, is available for pregnancies determined to be at risk. Also pregnancies who have findings of congenital heart disease and/or cleft palate detected by ultrasound examination may be offered prenatal testing. Genetic counseling may be helpful for families who may have DiGeorge syndrome. Because most of the signs of this cluster of defects can also be inherited as autosomal recessive or x-linked traits, only genetic testing of both parents can determine with any certainty the likelihood these anomalies occurring in any subsequent children.