CamRare Family Resources
Genetic testingThis page is dedicated to answering common questions about genetic testing. If you would
like an in-depth explanation of DNA sequencing, the whole genome, and exome sequencing, follow this link by Dr Caroline Wright, a professor in genomic medicine.
What are genes, genetic testing and DNA?
DNA is commonly referred to as the building blocks of life. DNA is the genetic code that causes us to turn from a single fertilised egg cell into the complex people we are today. On the smallest level, DNA is made up of simple nucleotides A,C,T,G. Genes are groups of these nucleotides that, when read together, form a protein. Lots of Genes next to each other form a chromosome. You have 46 chromosomes which store all of your DNA.
Genetic testing aims to find out where in the DNA an error has occurred that could be causing symptoms.
What are genes, genetic testing and DNA?
DNA is commonly referred to as the building blocks of life. DNA is the genetic code that causes us to turn from a single fertilised egg cell into the complex people we are today. On the smallest level, DNA is made up of simple nucleotides A,C,T,G. Genes are groups of these nucleotides that, when read together, form a protein. Lots of Genes next to each other form a chromosome. You have 46 chromosomes which store all of your DNA.
Genetic testing aims to find out where in the DNA an error has occurred that could be causing symptoms.
Types of genetic testing
Genetic conditions can be caused by problems with individual genes, groups of genes or chromosomal. Each test is different as they will look for specific genes, groups of genes or chromosomes.
Specific gene or condition
Some genetic diseases have been known for decades and are well-studied. This has led to doctors knowing exactly which gene or genes cause this condition. In these cases, doctors can perform a specific test to look for this condition.
Cystic fibrosis is one example of this. If doctors suspect cystic fibrosis, they can test for mutations (changes) in the CFTR gene, and if present, they diagnose Cystic fibrosis.
Microarray
A microarray is a test to look at chromosomes, not individual genes. A child receives 23 chromosomes from mum and 23 from dad. However, in some cases, parts of these chromosomes are damaged, leading to multiple genes being deleted or duplicated. Depending on the size and location, these can cause disease or have no effect at all. A microarray test looks at the chromosomes to see if any area has been deleted or duplicated.
https://www.nationwidechildrens.org/family-resources-education/health-wellness-and-safety-resources/helping-hands/microarray-analysis-testhttps://rarechromo.org
Whole genome sequencing (WGS)
WGS sequences all your 100,000 genes. Although the whole genome is sequenced, often only part of the data is analysed. The area analysed is dictated by the patient’s symptoms and the function of the genes. The test looks for any differences between your genes and the general population to see if they can identify which gene or genes may be causing the disease.
More information on genetic diseases
https://www.eastgenomics.nhs.uk/for-patients-and-carers/your-questions-answered/
https://buckup-cuh-production.s3.amazonaws.com/documents/Patient_Information_for_Rare_Disease_v2.2_IoHUwNE.pdf
https://buckup-cuh-production.s3.amazonaws.com/documents/Patient_Information_for_Rare_Disease_-_Easy_Read_v2.1_02YIIOC.pdf
Benefits and drawbacks of genetic testing
Benefits
- In many cases, it provides people with a diagnosis. Between 11-55% of patients get a diagnosis after genetic testing.
- Having a diagnosis allows you to join condition-specific support groups. Or larger umbrella groups where there aren’t disease-specific groups
- A diagnosis makes looking ahead to treatment options and planning for the future more manageable. 25% of genetic testing leads to new treatment pathways
- In cases where not much is known about the disease having a diagnosis allows you to follow and participate in research over the years.
- It can give you information about how this condition is inherited and the risks of future children having this condition.
Drawbacks
- Even though genetic tests may confirm a diagnosis, there may not be any treatment for it as it is a rare disease.
- Genetic mutations don’t always correlate to the severity of the disease. There are cases where people have the same condition and same mutations but very different symptoms and long-term outcomes.
- It may raise more questions. Sometimes mutations occur in regions that we don’t know what they do. These are variants of unknown significance. The doctor can tell you this area is different, but not what that means for the child.
https://geneticalliance.org.uk/information/service-and-testing/
Why has or hasn't genetic testing been offered to your child?
Genetic testing is one of the best ways to confirm a diagnosis of a specific genetic disease. Doctors may order genetic testing if they think your child has a specific disease, or they will order whole genome sequencing to test for many diseases at once.
Like all medical tests, doctors should only perform a test if there is a reason (indication) to do so and the result will help the patient. NHS England has published a list of 621 reasons to do genetic testing and what type of test to do. If your child doesn’t have one of those reasons, then there may be no benefit in doing a genetic test. That said, even if your child has one of these reasons (indications) for testing, they may not receive a test right away. Doctors don’t order every test possible but usually start with the most likely cause and work to the least likely based on the patient’s individual symptoms. Doctors may want to rule out other conditions before doing genetic testing, but if you are concerned, discuss genetic testing with your doctor.
https://www.england.nhs.uk/publication/national-genomic-test-directories/
What does the test involve?
Genetic testing starts with a simple blood test to get your child’s DNA. In some cases, they will compare your child’s DNA to the parents’ DNA, requiring a blood sample from the parents as well. Sometimes mutations in DNA don’t cause harm, so if you and your child have the same mutation and you are healthy, then the chances are this mutation isn’t causing your child’s symptoms.
How confidential is it?
In short, very. If you have DNA testing on the NHS , and we don’t recommend you go anywhere else, your DNA results are like all other confidential healthcare tests between you and the medical team. Insurance companies will not be given access to your information without your specific consent, and this is protected by confidentiality and the government’s code on genetic testing.
If you have WGS, you may be asked if you want to donate your sample, genome sequence and health data for research. If you agree, your samples will be stored securely, and your data will be added to the National Genomic Research Library, which is a secure national database of de-identified genomic and health data managed by Genomics England.
https://www.eastgenomics.nhs.uk/for-patients-and-carers/your-questions-answered/
https://www.gov.uk/government/publications/code-on-genetic-testing-and-insurance
Is it genetic if no one else in my family has the disease?
Up to 80% of rare diseases are genetic, and 70% of those start in childhood. If your child has a rare disease, there is a strong possibility that it could be genetic. There are two ways your child can have a genetic disease if no family members are affected.
1. It’s a recessive condition. When a child is conceived, 23 chromosomes come from the mum and 23 chromosomes come from the dad. The two sets of chromosomes join to form 23 pairs of chromosomes (46 total). This means you have two copies of every gene, one from mum and one from dad.
In some diseases, you need two faulty genes in order to have any symptoms. Children who have these diseases receive a faulty gene from mum and a faulty gene from dad and only together this causes disease. As you need two faulty genes it is common for there to be no family history of this genetic condition. Cystic fibrosis is one such recessive genetic disease. For more information on inheritance, look at this link
https://med.stanford.edu/cfcenter/education/english/Genetics.html#:~:text=Cystic
%20fibrosis%20occurs%20when%20both,mutated%20or%20not%20working%20pro
perly.
2. The other way children can get a genetic disease without a family history is pure random mutation. When a child is conceived and DNA is combined, the process isn’t perfect. In all people, there are random changes in the 100,000 genes we have. Most of the time, these changes do nothing, but sometimes these changes lead to disease.
Useful resources
Our complete guide on genetic testing by Dr Caroline Wright https://rarechromo.org/media/information/Other%20Topics/DNA%20sequencing%20(whole%20genome%20and%20exome)%20FTNW.pdf
https://www.eastgenomics.nhs.uk/for-patients-and-carers/your-questions-answered/