Why do we resemble our parents? How does a single cell grow into a whole human? Genetics is the science that tries to answer these questions. Humans, like every other living creature, are made up of cells. We all start off as one cell at the time of fertilization. This cell contains two sets of genes, one from our mother and one from our father. For ease of storage and access, the genes are packaged up into 46 chromosomes. As the single cell divides the genes are copied so that every new cell possesses the full complement of genetic material. Genes are made of a chemical called DNA. Each cell holds about 2 m of DNA.
Humans have approximately 30 000 genes stretched out along their DNA. Each gene acts as the recipe for the production of a protein and together they make up the recipe book or blue print for you and me. Different genes or recipes are read at different times in different cells in response to the requirements of our bodies.
Sometimes genes, like recipes or blueprints, may have spelling mistakes in them or have bits missing. When this happens the proteins are either not produced or are abnormal. Genes, with these mistakes or mutations, function abnormally and so cause genetic disorders. As genes are passed on from one generation to the next, genetic disorders often run in families. These mistakes can arise when a cell does not accurately copy its DNA. A mistake or variation in a single DNA letter can lead to disease.
Someone from your Haemophilia Centre has already explained the nature of the disorder and the manner in which it can be passed down through your family. If you require further information, or you are unclear about what you have been told, please ask for clarification or more help.
Genetic testing can tell us which people in your family have the condition and who are ‘carriers’ who might pass the disorder on to their own children. Simple tests of the defective clotting factor (coagulation factor) can sometimes tell us if a person is affected by the disorder or a carrier. Sometimes the level is normal, although a person is carrying a defective gene. With modern genetic techniques it is usually possible to locate the faulty genetic change in each family, although this can sometimes take time. Although many families may have the disorder, it is common for each family to have its own unique genetic change.
1 What is the purpose of obtaining a blood sample? It is very useful to know what the exact mistake in the DNA is that is causing the disorder in you/your child. Sometimes this helps us to be warned about how the disorder may respond to treatment in the future. Measurement of the blood coagulation factor level does not always clearly indicate if there is a genetic mistake present or not; analysis of the DNA is a more accurate way of telling this. For this a special type of blood sample is required from which the DNA can be extracted. A second sample may be taken from you on a separate occasion to confirm the result of the initial test.
2 Where will the blood sample be tested? The tests needed to detect a change (‘spelling mistake’ or bit missing) in DNA are specialized. Some of them are performed locally, but depending upon the nature of the disorder, it may be necessary to send your blood sample away to one of a small number of specialized laboratories. In all these, there are strict regulations in place to ensure complete confidentiality of your details.
3 How long will the test take? The answers to genetic tests often take some time to obtain. Depending on the type of disorder and the purpose of testing the time course may take weeks, months and sometimes up to 1 year if you have one of the less common, or complicated disorder. Your doctor may be able to give you an estimate of the time it will take.
4 How long will my blood sample be stored? Sometimes it may not be possible with existing methods to find the genetic change in your family. In this case, the DNA will be stored until new tests are available. It is usual practice to store DNA samples indefinitely. Other new tests relevant to the disorder may arise in future, which will help us understand more about the mechanisms of the disorder.
5 What are the risks of genetic testing? In addition to information on the inheritance of a bleeding disorder, the results from these genetic tests are likely to be able to determine other information, such as confirmation of whether a child's parent is as assumed by the family. Therefore, occasionally unexpected results about family relationships arise from these tests, which, if known, could cause embarrassment within a family. If it is found, for example, that an individual's parent is different from that assumed by the family significant psychological problems can be caused and this may cause harm to the person being tested and other family members. The studies performed will be specific for the disorder known to be in your family. They will not exclude all forms of possible bleeding disorders.
6 What else might be done with my blood sample? We might want to use your sample to help develop or refine tests for bleeding disorders. In such cases your blood samples would not be linked back to you. The results would therefore be completely anonymous. From time-to-time it is very useful to run tests on a series of DNA samples anonymously to compare how some common changes in the DNA are which are not responsible for the condition. If your sample is used for such testing, no one will know whose it is, and there will be no comeback to you and your family.
7 Who gets to know about the results? The results will be told to you personally. Your family doctor will be sent the result.
8 Why might it be useful for other members of my family to know about the results? Information about the genetic disorder in you/your child is likely to be of benefit to other members of your family. It may, for example, be used to discover if a woman is a carrier and therefore if there is a risk of passing on the disorder to her children. With your permission we would like to be able to make the information about your genetic change available to doctors looking after other people in your family if they ask.
9 Are my genetic results going to be stored anywhere other than in my hospital and GP case records? There are local and national confidential databases, which keep information about genetic disorders of coagulation. We would like to record the information about your gene change. These databases are secure and protected.
If you would like to have your blood tested please read the consent form.
|(A) Patient details|
|Surname ……||Consultant ……|
|Forename ……||Hospital number ……|
|Date of Birth ……|| |
|(B) Collection and usage of samples|
|I, …… (print name) give consent for a blood sample to be taken from …… (myself or name of child) and the genetic material extracted, stored and tested for …… (specify disorder).|
|Please initial the boxes below to indicate your consent|
| The purpose for obtaining this sample and the potential implications has been explained to me and I have had an opportunity to have my questions answered|
| I have read and understood the above information about genetic testing|
| It is the intention to store the sample indefinitely|
| If no relevant test is currently available, I agree to the sample being stored until such time as an appropriate test is developed and the sample may then be tested|
| I understand that it may be necessary to use part of the sample anonymously, for example, for quality assurance or development of new tests|
|Signed …… (Patient/parent/legal guardian – delete as appropriate)||Date ……|
|(C) Use and availability of results|
| I hereby give consent for clinical and genetic information that may be relevant to other family members to be made available to relevant health care professionals|
| I agree to the results being entered into local confidential databases|
| I agree to the results being entered into national confidential databases|
|Signed ……||Date ……|
|(Patient/parent/legal guardian – delete as appropriate)|
|(D) Person obtaining consent|
|I have explained to the above patient/parent/legal guardian the purpose of obtaining a sample for genetic studies and their implications.|
|Signed ……||Date ……|
|Print Name ……||Position …|
|Job Title ……|| |
A photocopy of the completed form should be given to the patient, the original filed in the patient's case notes and a copy filed in the family genetic record file.