Sometimes we offer to take blood for testing on the same date as your appointment or we may ask you to go away and decide whether or not you want a genetic test. The main types of testing we offer are chromosome tests and DNA tests.
A chromosome test
Chromosomes are structures made up of hundreds of thousands of genes and are found in the centre of all our body cells. Chromosomes are large enough to be seen under a microscope once they have been stained with certain dyes. They can be ordered and numbered based on their unique banding pattern.
Each human cell has 23 pairs of chromosomes. Each pair consists of one chromosome inherited from our mother and one from our father. The 23rd pair are the sex chromosomes usually two X chromosomes in females and an X and a Y chromosome in males. This pair determines whether we are female or male.
A chromosome test can identify certain chromosomal abnormalities such as missing or extra chromosomes or rearrangements. The results from this test are usually available in 4-6 weeks.
A DNA test
Genes are individual instructions stored in the chromosomes and they are made up of DNA (deoxyribonucleic acid). Each gene has a different function. Most of them tell us how to make one of the many proteins that our bodies need to work properly
A DNA test looks for gene changes in a particular set of genes. Some genetic disorders are caused by changes in individual genes. Testing for these conditions can be complex and we sometimes need to send samples to genetic laboratories elsewhere in the UK or overseas that specialise in a particular condition. The results from these tests are usually available in 2-3 months but sometimes it can take much longer.
Testing in different situations
Carrier testing this is usually taken by people who dont have a particular disease, but might carry one copy of a genetic change. Couples considering having children whose families have a history of a recessive genetic disorder often have a carrier test. To be affected with a recessively inherited condition a person needs to have two copies of a changed gene one inherited from each parent.
Diagnostic testing this is carried out on a person who is already affected or thought to be affected with a genetic condition. This test may clarify the condition the individual has to help with their management. A diagnostic genetic test can often help other family members as it means that they can, if they wish to, have a predictive or carrier test to determine their own situation.
Pre-symptomatic testing or predictive testing a person may choose to have this type of testing if they have no symptoms of a genetic condition which is in their family but wish to know if they may have the condition in the future. This type of testing often involves several appointments as the outcome may have an impact on both their future medical management and life choices.
Pre-natal diagnosis this is a genetic test that is carried out on the unborn baby. A small sample of the placenta or cells shed from the baby are taken (depending on the technique used) and this is then tested to find out if the baby has inherited a specific genetic change.
Pre-implantation genetic diagnosis is carried out on embryos that have been fertilized in the laboratory using in vitro fertilisation procedures (IVF, sometimes known as test tube babies). Embryos are usually tested for the presence of a specific gene change; only embryos without this gene change will be implanted into the mothers womb. This technique is currently only available in certain circumstances.