Chromosome - 22q11 Deletions
This information aims to explain what a 22q11 deletion is and how it affects people.
What is a 22q11 deletion?
Genes are the blueprint of the body. When one or more genes are lost the blueprint is changed, often leading to problems from birth and learning difficulties. Genes are made of a chemical called deoxyribonucleic acid, usually abbreviated to DNA, and are contained inside larger structures called chromosomes. Chromosomes are found in every cell of the body.
Most people have 23 pairs of chromosomes (46 in total). One of each pair comes from the mother and the other from the father. Chromosomes are numbered 1(the largest) to 22 (the smallest pair); the 23rd pair are called sex chromosomes because they determine whether a person is male or female. Each chromosome has a “q” arm (which is long) and a “p” arm (which is short). The genes are arranged in clusters along these arms.
Someone with a 22q11 deletion has a very small piece missing from the “q” arm of one of his or her chromosome 22s.
How is it detected?
The piece of missing chromosome is so small that it cannot be seen under a microscope. A special test called the FISH test (fluorescence in situ hybridisation) is used to show whether or not this region of chromosome 22 is present. A test called array CGH may also find 22q11 deletions.
How common is it?
22q11 deletion is one of the most common chromosomal abnormalities. It is thought to be present in 1 in 3000 – 4000 births. It may be even more common than this because some people who carry the deletion never come to medical attention.
Why did it happen?
The chromosome deletion was present in either the egg or sperm from which the baby was conceived. DNA copying errors frequently occur when the eggs and sperm are made. The process of copying the DNA when the eggs and sperm are made is never completely perfect. There is nothing that either parent could have done before or during the pregnancy to prevent the deletion from happening nor could they have done anything to cause the deletion to occur. It is important to understand that this is no-one’s fault.
How will my child be affected?
22q11 deletion is associated with at least 2 different syndromes. A “syndrome” is a recognised collection of symptoms or findings/abnormalities, which commonly occur together. Syndromes are commonly called after the doctor who first described them. 22q11 deletion is found in both Di George syndrome and Shprintzen (velo-cardio-facial) syndrome.
However many children with 22q11 deletions do not have all or even any of the problems associated with either of these syndromes. The affect of this deletion is extremely variable and very difficult to predict. Over 100 different features are found more commonly in individuals with 22q11 deletions than in the general population. The chance of any one child with a 22q11 deletion having any one of these is small. Once a child has been diagnosed, a medical assessment is undertaken to make sure any potential problems are checked for and the child is referred to relevant specialists.
Medical problems associated with 22q11 deletion
Heart problems Many children with 22q11 deletion are born with a severe heart defect. Even if your child does not have a known heart defect, assessment by a heart specialist (cardiologist) and a heart scan will be offered. The chance of finding a heart defect in this situation is very low but it is important to find out, as effective treatment can be given if a heart problem is detected.
Developmental delay, learning difficulties Many children have some degree of delayed development. It is important that they are monitored regularly to identify problems early and provide appropriate support. Some children may develop behavioural or psychological problems.
Palate Cleft palate or weakness of the palate is common and may lead to feeding difficulties and particularly to speech problems. Children will be referred to the cleft lip and palate team and a speech therapist for assessment.
Hearing, tonsils and throat problems A few children have repeated ear infections and hearing impairment.
Kidneys Around 30% of children will have kidney abnormalities which can be detected on ultrasound scan.
Immune system A few children with 22q11 deletions are prone to infections because they have a problem with their immune system. Most children will grow out of this by their first birthday, but a few will continue to have problems. All children will be referred to an immunologist for assessment.
Endocrine problems Newborn babies sometimes have low calcium levels and require supplements. It is very unusual to have problems later in childhood. Some children may have short stature and growth problems which may require referral to a growth/hormone specialist.
Neurology Occasionally children will have symptoms such as fits or problems with balance. Advice from a neurology specialist may be helpful in these cases.
Will it happen again?
In around 10% of cases the 22q11 deletion is inherited from one parent. Both parents will be offered a blood test to find out whether one of them carries the deletion. If both parent’s chromosomes are normal the chance of having a further baby with the deletion is low (less than 1%). If one parent has the 22q11 deletion then that parent has a 50% (1 in 2) chance of passing on the deletion to each of his or her children.
The FISH test can be carried out during pregnancy to test an unborn baby. The FISH test shows whether the baby has the deletion, but cannot predict how severely affected the individual will be. There may be multiple problems or no problems.
Detailed ultrasound scanning will be able to detect some defects. They can look for a cleft palate, but these are very difficult to see on scan. A foetal heart scan (foetal echo) at around 20 weeks can detect some heart defects.
For more information
If you need more advice about any aspect of 22q11 deletions, you are welcome to contact:
Northern Genetics Service
Institute of Genetic Medicine
Newcastle upon Tyne
Telephone: 0191 241 8600 (8.30am to 5.00 pm Monday to Friday)
Fax: 0191 2418799
If you would like further information and the opportunity to talk to other parents you can contact:
15 Meriden Avenue, Wollaston, Stourbridge, West Midlands DY8 4QN
Freephone: 0800 389 1049
Telephone: 01384 821227 (this is also a fax)