DiGeorge syndrome is caused by the deletion of a portion of chromosome 22. Each person has two copies of chromosome 22, one inherited from each parent. This chromosome contains an estimated 500 to 800 genes.
If a person has DiGeorge syndrome, one copy of chromosome 22 is missing a segment that includes an estimated 30 to 40 genes. Many of these genes haven't been clearly identified and aren't well understood. The region of chromosome 22 that's deleted in DiGeorge syndrome is known as 22q11.2. A small number of people with DiGeorge syndrome have a shorter deletion in the same region of chromosome 22.
The deletion of genes from chromosome 22 usually occurs randomly in the father's sperm or in the mother's egg, or it may occur very early during fetal development. Therefore, the deletion is repeated in all or nearly all of the cells in the body as the fetus develops.
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