Your child’s doctor has suggested a test called a SNP array which may be helpful in investigating your child’s difficulties. This leaflet aims to explain what this test is and what the results might mean.
What are chromosomes?
DNA acts as our instructions, telling our bodies how to grow and develop. A gene is a section of DNA. Genes are stored on structures called chromosomes. If genes are like the recipe books, the chromosomes are like the bookshelves. The majority of cells in our body have 23 pairs of chromosomes (one inherited from each parent), and these are numbered from pair 1 to pair 22, with the final pair being the sex chromosomes (XX in girls and XY in boys).
What is an SNP array?
SNP array stands for single nucleotide polymorphism array. It is a test that looks at our chromosomes in detail to see if there are any areas of the chromosomes with extra or missing genetic material which could explain the difficulties your child is experiencing. These tiny genetic changes are called microduplications (extra genetic material) or microdeletions (missing genetic material). This test does not detect spelling mistakes in individual genes and will only pick up some genetic diseases.
Many people have small changes on their chromosomes that do not cause health or development problems. However certain changes may cause a variety of difficulties such as developmental delay, learning and behavioural problems and physical health problems.
How is the test done?
An SNP array is a blood test which is taken from your child. The blood sample is then sent away to a laboratory for analysis. It usually takes about 3 months for a result to be available.
What results could we get?
1. A Positive Result
The results might show a chromosome change that explains (or partly explains) your child’s physical, medical and/or learning problems. This means your child will have a genetic diagnosis. Some benefits of this might be that if other parts of the body are affected these can be monitored or treated quickly. Also specific support groups might be available. In some cases, we do not know very much about the chromosome change and so the information we can give you might be limited.
A positive result may help your doctor to understand the chance of you having another child with the same genetic difference. It’s important to remember that children with the same genetic difference may have different patterns of development.
2. A Negative Result
The test might not find a chromosome change to explain your child’s physical, medical and/or learning problems. This does not mean that you child does not have a genetic disorder but just that this test has not found the answer. Your doctor will talk this through with you and talk about whether any other genetic testing is suitable for your child.
3. An Incidental Finding
When doing the Chromosome Array test, there is a small chance that we might find something unexpected. This is a chromosome change that is unrelated to your child’s physical, medical and/or learning problems but that could cause another genetic disorder. This is called an incidental finding. This could be important for your child now or when they are an adult and planning their own family. It could also be important for other members of your family if they have the same chromosome change.
4. One of Uncertain Significance
The results may show a chromosome change where we are not sure if it causes any problems or not. Sometimes there are extra tests that can help us understand this further. Sometimes we can’t work out whether it is causing any problems or not and so it remains uncertain.
If any genetic change is identified, we will call you back into clinic to discuss this. We would talk to you about the result and seek advice from the genetics doctors about whether any referrals are needed.
Are there any down sides to testing?
Some parents and families can feel anxious about going ahead with genetic testing; results which leave uncertainty about their significance can increase this anxiety.
Some parents worry about how the results might impact on their child in the future, for example if applying for certain jobs or insurance; there is currently an agreement with insurance companies that they cannot ask about genetic testing, but this might change in the future.
Positive results can occasionally lead to feelings of guilt of blame if the change has been inherited from a parent.
Occasionally we find unexpected and incidental changes which are not directly relevant to your child’s health now but might give information about their health as an adult. While this information might aid monitoring of their health, it is important to consider that by finding this out now, your child has not been able to decide for themselves whether or not to be tested.
Does my child have to have the test?
No, it is up to you whether you want your child to have the test. If you do not want your child to have this test at this point in time, please talk to your child’s doctor about other options.
Key Points
- A Chromosome SNP Array looks at the chromosomes in detail but not at individual genes.
- This may find a cause for your child’s physical, medical and/or learning problems.
- This may find unexpected or uncertain results.
- Results may be relevant to your wider family. Informing them would be done after a discussion with you.
- It takes about three months to get results.