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A deletion syndrome is a genetic disorder caused by the deletion of genetic material. Several congenital conditions including Cri Du Chat Syndrome, DiGeorge Syndrome, 22q13 deletion syndrome, and Phelan-McDermid Syndrome are examples of deletion syndromes. These genetic disorders can vary widely in severity and they can be observed in populations all over the world. Some people are at greater risk than others.
There are several ways that a deletion syndrome can develop. One is a mistake during the production of egg or sperm cells that results in snipping a segment from a chromosome. Sometimes, early errors during fetal development lead to partial deletions on the chromosomes. More rarely, a parent carries a chromosome with a deleted segment in a condition known as a balanced translocation where genetic material is moved around. The child may inherit the chromosome with the missing piece and not the rest of the genetic data, resulting in a deletion syndrome. In a condition known as a frameshift mutation, the base pairs that follow a deleted string of DNA are not read properly and the proteins coded with that DNA are incorrect.
In some cases, deletion of a segment of chromosome results in abnormalities that are inconsistent with life. Typically, a miscarriage will onset very early in fetal development. Women who experience recurrent miscarriages can request genetic testing of the abortus, as well as herself and her partner, to determine whether a genetic disorder such as a deletion syndrome was involved and to explore possible causes for the miscarriages. If one of the parents has a balanced translocation, for example, this could explain the miscarriages.
Other deletion syndromes result in a fetus that can be carried to term, but may have a variety of disabilities. Deletion syndromes can involve any part of the body and in a contiguous gene deletion syndrome, multiple genes may be involved. A child may be born with physical anomalies and can develop intellectual and cognitive disabilities due to changes that occurred inside the brain.
Sometimes, people have missing genetic material and experience no obvious ill affects until later in life. Others may have relatively mild symptoms. The severity of a deletion syndrome depends entirely on the location of the missing segment of DNA. Genetic testing can be used to identify missing or translocated DNA. Some deletions are so rare that they do not have names, because they have not been observed and researched yet. Others are relatively common and can be highly recognizable even without genetic testing.
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