Living with dementia magazine April 2009
Is dementia hereditary?
Many people with dementia are concerned that their disease may have been inherited and that they may pass it on to their children. Family members of people with dementia are sometimes concerned that it might be more likely to develop dementia themselves.
Here, Professor Nick Fox, Honorary Consultant Neurologist at the Institute of Neurology in London, provides some answers.
Is dementia inherited?
The majority of dementia is not inherited, but this depends very much on the particular cause of dementia. Some (rare) causes of dementia are very clearly 'inherited', for example Huntington's disease. This is an 'autosomal dominant' disease which means that only one faulty copy of the gene is needed in order to inherit the disease.
If you have inherited the gene you will get the disease if you live long enough. It does not skip a generation. Some other dementias have both inherited and non-inherited forms. In the case of fronto-temporal dementias, 30 to 50 per cent of cases are inherited. Most cases of Alzheimer's disease are not inherited.
Is Alzheimer's disease inherited?
Many people fear that Alzheimer's disease in the family may be passed on to children and grandchildren. In the vast majority (99 per cent) of cases, this is not so. Like many conditions, having Alzheimer's disease in the family does very slightly increase the chance of people in later generations getting the disease.
The most important risk factor for Alzheimer's disease is age. Because Alzheimer's disease is so common in people in their late 70s and 80s, having a parent or grandparent with Alzheimer's disease at this age does not change your risk compared to the rest of the population.
In a very small number of families, Alzheimer's disease is inherited. The impact of these genes was first discovered more than 100 years ago and accounts for less than one per cent of all cases of Alzheimer's disease.
For these families, this is a devastating legacy. The disease usually develops at a much earlier age than usual, with individuals being affected as early on as their 30s. Three genes, APP, PS1 and PS2, have been identified as causing this early-onset inherited form of Alzheimer's disease.
Defects in these genes can now be tested, and if the particular gene is known, individuals may choose to have predictive testing. Predictive testing is always preceded by careful genetic counselling.
Is there ongoing research into inherited dementia?
Inherited dementias have provided great insights into the causes of different dementias, largely through members of affected families generously volunteering to participate in research studies. Research is very active in many different centres around the world.
Last year, an international consortium (Dominantly Inherited Alzheimer Network - DIAN*) was set up to study familial Alzheimer's disease to try and understand more about the causes and earliest features of this devastating condition. Find out more
If you have/had a parent with an autosomal dominant mutation causing Alzheimer's disease or fronto-temporal dementia and you would like information about taking part in research, please write to the Dementia Research Centre, Box 16, Institute of Neurology, London, WC1N 3BG.
For more information on inherited risk and other risks associated with different types of dementia please read Am I at risk of developing dementia? (450) and Genetics and dementia (405). To order a free copy of either, call Xcalibre on 01753 535751, or email email@example.com