Why did this happen to us?

This is generally not known as 90% of patients who have the deletion, do not have an affected parent, therefore, the change in their chromosome 22 is a "new mutation" in them.

There is nothing that either parent could have done before or during the pregnancy to have prevented the deletion from happening or could have done to have caused the deletion to occur. This is a defect of the human race not of one particular person.

It is vital to understand that this is no-ones' "fault".

The chromosome deletion was present in either the egg or sperm from which the baby was conceived. In other words the baby was destined to be born with DiGeorge syndrome/VCFS from the instant of conception.

Could this happen again?

To assess the chances of recurrence parental blood samples have to be analysed in order to establish whether one parent also has a chromosome 22 with the deletion.


If the parents' chromosomes are normal, then the chance of having a further baby with the deletion is quite low (less than 1%). If the deletion is present, then that individual has a 50% chance of passing on the deletion to each of his or her children.

The chance of having more than one child affected when the parent has the deletion is random (like the chance of tossing a coin and getting "heads" twice in a row).

It is important to point out that when a child receives the chromosome 22 with the deletion, the medical problems can be quite variable as it is not possible to predict the degree to which an individual is affected by the deletion. There may be multiple problems or no problems. Also the degree of severity of those problems is very variable. For example from a very mild heart problem to a very severe one, or no heart problem at all.

What are the tests to diagnose the deletion?

The usual method of chromosome analysis is called karyotyping. This looks at the physical structure of the chromosome under a microscope and is used for detecting large chromosomal rearrangements or deletions.

The 22q11.2 deletion is a sub-microscopic deletion and is therefore too small to be seen by this method so the "FISH" test (Florescence In-Situ Hybridisation) is generally performed.

FISH looks directly at the specific area on the 22nd chromosome where the geneticist believes the deletion will lie. Probes, which are tiny segments of man-made DNA which match DNA segments 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 22's then two stained probes will appear (or 'light up'). If there is a deletion on one of the chromosome 22's, the probe will have nowhere to stick to, and only one probe will appear.

The FISH test can be carried out during pregnancy to test an unborn baby through two methods:

à CVS - chorionic villi sampling - this is carried out at 12 weeks of pregnancy and involves having a piece of placenta taken either through the cervix or the abdomen. It is thought to carry a 1 - 2% risk of miscarriage but gives the advantage of an early and quick diagnosis.

à Amniocentesis - this is carried out at 16 weeks of pregnancy and a sample of amniotic fluid (the waters that surround the baby) is taken through a needle inserted through the abdomen. This carries a slightly lower risk of miscarriage but it takes longer to get a diagnosis as the sample has to be specially prepared over a period of a few days.

The FISH test can identify whether a foetus has the deletion but can not predict how severely the individual will be affected as there is no significant correlation between the size of deletion and the extent of anomalies.

Detailed scanning at specialist centres dealing with foetal medicine will be able to detect certain defects, such as a cleft palate. A foetal echocardiogram (foetal echo) looks at the detailed structure of the heart, how the blood flows through it, the main blood vessels around the heart and can detect most heart defects. These can be carried out at around 20 and 28 weeks of pregnancy.

These type of scans can help a medical care plan to be put in place to prepare for the baby's arrival. However, many individuals have the deletion but no major structural/organ abnormalities.

N.B. It is recommended that families considering prenatal diagnosis request prompt referral to their local genetics department as early as possible in pregnancy to allow time for arranging tests. It may be appropriate for patients already known by the genetics clinic to contact the clinic direct so as to avoid delay by being referred via the antenatal clinic

Is the deletion a rare genetic disorder

It is currently estimated that as many as 1 in 1,800 of the population may be affected by the 22q11.2 deletion. It is the most frequently occurring chromosome deletion and the second most common cause of congenital heart defects.

The frequency of diagnosis has increased enormously over the past few years as the FISH test used to identify the deletion has only been commonly available in the last four or five years and many individuals are now found to have the deletion who only have very mild symptoms. Also a child may be diagnosed and then as a result of genetic investigations a parent is also found to carry the deletion but has no obvious symptoms.