A blood test can be carried out to look for the PSEN1, PSEN2 and APP mutations and APP duplications that are known to cause familial Alzheimer’s disease. These tests are complicated to conduct so it can take several months to get a result. If an individual with symptoms of Alzheimer’s disease undergoes a blood test to look for these mutations, their next of kin should be involved in the discussion about genetic testing in view of the implications for other family members. A specific consent form must be completed in order to process these blood samples. This is known as diagnostic genetic testing.
Although a negative test result is very reassuring, it cannot completely exclude the possibility that an individual’s Alzheimer’s disease is familial as it is possible that other genetic causes remain to be discovered. However, it does make it much less likely.
Diagnostic Genetic Testing
Diagnostic genetic testing is only appropriate for a very small proportion of people with Alzheimer’s disease. It is typically offered when someone has developed symptoms of Alzheimer’s disease at a young age and has a strong family history of other relatives developing a similar illness at a similar age. It may also be offered to individuals with early onset Alzheimer’s disease who have a censored family history. No genetic test is available on the NHS for risk genes that may be associated with late-onset Alzheimer’s disease. Such a test would not be useful as possessing a risk gene does not mean that an individual will develop Alzheimer’s disease, or they may still develop it even if they don’t carry the risk gene.
Predictive Genetic Testing
If the precise familial Alzheimer’s disease mutation affecting an individual is known, it is possible for that individual’s adult children and siblings to undergo genetic testing in order to find out whether they have inherited the mutation. This type of testing, which is conducted in individuals who are currently well and have no symptoms of Alzheimer’s disease, is known as predictive genetic testing. Predictive genetic testing is only done after a period of genetic counselling, during which the individual sees a specialist on a number of occasions to discuss all the implications of receiving either a positive or negative test result. Genetic counselling is not counselling in the psychological sense of the word but a process of accurate information giving, explaining all the facts and options to an individual as clearly as possible so that they may make their own decision about whether to proceed with genetic testing. The sessions are spread over a minimum of 3-6 months and are followed by a ‘cooling off’ period before the test is actually done, during which people may decide to decline or postpone taking the test. If a relative is thinking about finding out whether they have inherited the faulty gene they will need to be referred to a genetics or neurogenetics clinic by a GP or hospital consultant. It is often helpful to discuss this with the medical team caring for the individual with Alzheimer’s disease first.
Choosing to undergo predictive genetic testing requires very careful thought and is not the right decision for everyone. It is also perfectly acceptable for an individual to decline testing after undergoing a period of genetic counselling. Reasons why people may want to have a genetic test include: wanting to end uncertainty, to help them in making life choices/plans for the future, to make family planning choices and to inform other family members of their risk eg. children. If someone is considering genetic testing it is a good idea to think about how the testing procedure and test results may affect their relationship with their partner and other family members. In many cases the genetic testing process brings families closer together but in some cases, the process can cause tension and complications within a family. An individual’s test result can give other family members unwanted information about their own risk. It is important to remember that different members of a family may have different feelings about testing and that these feelings should be respected. Equally, it should be remembered that taking a genetic test is a very personal choice and an individual should never feel pressured into taking it by family, friends or healthcare professionals.
Genetic counselling provides an opportunity for an individual to consider their options in a broad range of areas including finances, insurance, employment and reproductive options. For example, the Human Fertility and Embryology Authority (HFEA) have recently granted a licence allowing testing for PSEN1, PSEN2 orAPP mutations for couples who wish to pursue preimplantation genetic diagnosis (PGD). PGD is available to couples if there is a specific genetic mutation that is known to run in the family, although the individual undergoing PGD does not necessarily need to find out whether they carry the mutation themselves. It is a lengthy and complex process involving assisted reproductive technology, which in other circumstances is offered to couples with fertility problems. The chances of success depend on various factors and there are a number of criteria that must be fulfilled if a couple is to be considered for PGD. More information about can be found on the Guy's and St Thomas' Centre for Preimplantation Genetic Diagnosis website.
Genetic Alliance UK is national charity of over 150 patient organisations, including the familial Alzheimer’s disease support group, which aims to support people affected by genetic conditions by ensuring that high quality services and information are available to all who need them. Their website contains a number of useful resources including a directory of all NHS genetics services in the UK and a series of patient information leaflets. These cover various subjects including autosomal dominant inheritance, predictive testing and insurance.
Alzforum has recently published a two-part publication providing information about PGD. These articles have been informed by people who have used the method themselves. Part 1 provides details on the technology itself, whilst Part 2 describes some things to think about when deciding to use PGD. You can access both parts by clicking on the two links below: