Deborah Hung Copenheaver, M.S.
Childrens National Medical Center
Washington, D.C.
VCFS is caused by a microdeletion (small missing piece) of chromosome 22 at a region identified as the q11.2 band. The deletion has been detected in 85-90% of patients clinically identified as having VCFS. Two methods are usually used to detect the deletion. One of the methods is karyotyping, or chromosome analysis, which looks at the physical structure of the chromosomes. Large chromosomal rearrangements or deletions can be detected. Most of the deletions that cause VCFS are too small to be seen this way. In these cases, Fluorescent In Situ Hybridization (also known as FISH) is performed.
FISH looks directly at the area on the chromosome #22 that is associated with VCFS. Probes, which are tiny segments of man-made DNA that match DNA segment found at chromosome #22q11, are stained with a dye. Under proper conditions in the laboratory, the probes will anneal (or stick) to the matching area of chromosome #22q11. If a person has two normal (non-deleted) chromosome 22s, two stained probes appear. If there is a deletion on one of the chromosome #22s, the probe will have nowhere to stick to, and only one probe appears.
If a couple already has one child with VCFS or one partner of a couple has VCFS, they may wish to know if a pregnancy will be affected. If the affected individual has a deletion, the pregnancy can also be tested for the deletion. This can be done through chorionic villi sampling (CVS) or amniocentesis (amnio).
CVS is performed at 10-12 weeks gestation and involves having a piece of the placenta taken either through the abdomen or cervix. There is approximately a 1% chance of miscarriage associated with the procedure. Amniocentesis is a more commonly performed procedure. It is performed after 15 weeks gestation. Amniotic fluid (the fluid that surrounds the growing fetus) is taken through a needle inserted through the abdomen. The chance of miscarriage associated with the procedure is 1/200 – 1/400 depending on the center where it is performed.
Karyotyping and FISH can be carried out on the fetal cells obtained by amnio or CVS. Prenatal diagnosis can only tell whether or not there is a deletion. The degree to which an individual will be affected cannot be predicted.
Another option for a pregnancy that may be affected with VCFS, is a fetal echocardiogram (fetal echo). A fetal echo looks at the structure of the heart and shows the flow of the blood through the heart. Heart defects are found in 70-80% of people with VCFS, and knowing if a pregnancy has a heart defect may change how parents and an obstetrician prepare for a birth. A fetal echo can be performed after 18 weeks gestation.
Obviously, it is important to get prenatal care and ask your obstetrician about the prenatal options available in your area.
|
