What is 22q11.2 Deletion?
Most people have 23 pairs of chromosomes a total of 46, with one of each pair coming from the mother and the other from the father. Chromosomes are numbered 1 thru 22; the 23rd pair is called sex chromosomes because they determine a person's sex (male or female). Chromosomes are found in every cell in the body. Cells are so small that they, and the chromosomes they contain, can only be seen under a microscope.
When a baby is conceived with either too much or too little chromosomal material, birth problems can occur. This may include a whole extra chromosome, as in Down's Syndrome (an extra number 21); or a whole missing chromosome as in Tuner's Syndrome (a missing x); a piece of material missing or extra; or a complex rearrangement of chromosomal material is missing or extra; genes are generally missing or extra. Since genes are the blueprint of the body, when they are lost or extra, the body's blueprint changes, frequently leading to health problems and learning differences.
People with 22q11.2 deletion have a very small piece of chromosome 22 missing (thus it is called a deletion). The 22q11.2 tells everyone who works in genetics that the area missing is in a very specific spot on the "q" arm, which is also called the long arm of the chromosome. (Chromosomes are divided into two parts, the top half being called the "p" arm and the bottom half called the "q" arm). It is very important to know the location of a missing piece of chromosomal material in order to make general comparisons (although no two are exactly alike), because if two children have different areas of the same chromosome missing it would be like comparing "apples to oranges."
Although you can not see the missing piece under a microscope, you can prove it is missing by using a special DNA test called FISH (Fluorescence in situ hybridization). This test works like a lock and key. The person in the laboratory has the key which lights up (fluoresces) if it finds its matching lock in the chromosomes. If the lock is missing from one of the pair of the 22 chromosome, only one chromosome 22 will light up in the area in question (q11.2), confirming that the patients is missing material on chromosome 22.
The chromosome 22q11.2 deletion has been associated with a variety of clinical syndromes. The spectrum of the presenting signs and symptoms is inconsistent, having mild to severe implications and is ever changing. Almost every organ system may be involved, but at times one may encounter only minimal findings. There does not seem to be a definitive explanation as to why one patient has multiple system changes and another just a mild expression of the deletion. Early recognition of the existence of this deletion is imperative so that treatment of involved organ systems can be initiated, thus preventing or lessening the debilitating, uncomfortable and distressing problems for both the patient and family members.
Information above was provided from the book "Faces of Sunshine," the 22q11.2 Deletion. Edited by Donna M. McDonald-McGinn, MS, CGC, Brenda Finucane, MS, CGC, and Elaine H. Zackai, MD.