Deciding whether to get tested for an Alzheimer's gene

Taken from one of our 2012 magazine issues, find out why inherited forms of Alzheimer's disease are extremely rare, but for a small proportion of families who carry particular genes the results can be devastating. 

Liz Fox never really knew her father. When she was one year old he was diagnosed with early onset Alzheimer's disease and hospitalised. In 1981 at the age of 42 he died, when Liz was just four years of age.

Three decades later and Alzheimer's disease continues to affect her family. Liz is the youngest of four siblings and her eldest brother Tony, who is 41, was recently diagnosed with early onset dementia. He and another brother, Chris, have confirmed that they carry a rare mutated form of the presenilin-1 gene, which causes the development of early onset familial Alzheimer's disease. These genes account for less than one in 1,000 cases of Alzheimer's disease.

In the family

Although Liz had always suspected there was Alzheimer's 'in the family', it was only when Tony was diagnosed with dementia that the gene mutation was identified as the cause. Liz admits that since his diagnosis she has been plagued with worries that she may also develop dementia.

Liz says,

'After Tony was diagnosed with dementia and after testing he advised me that he has inherited the presenilin-1 gene. I wasn't that shocked as we had learnt from the family tree that dementia was in the family, although I was devastated for Tony, Jayne and their two sons.'

She adds,

'However, when I started reading that there was a 50-50 chance of us getting the gene it started to torment me and I found myself thinking I had dementia, for example, when I'd forget my keys. When my husband talked about plans for holidays with friends I began thinking to myself that I don't need to listen as I won't know what's what anyway.'

Glimmer of hope

Because of her worries Liz decided to see a consultant at St Mary's Hospital in Manchester about possibly being tested for the gene. After speaking to the consultant, however, Liz decided not to go ahead with it, deciding that she would rather have the 'glimmer of hope' that she had not inherited the gene.

She explains,

'Having a professional show you the high possibility that I could get this disease really scared me, but the thing she said to me was "What would you do if you got told you had it?" Once you have the knowledge there is nothing you can do to stop it, prevent it or take the knowledge of knowing you had it away.'

However, she also says that if a cure or something that would slow the progression of the dementia were available then she would get the test done to see whether she carried the gene.

Genetic factors

In the meantime Liz remains very keen on raising awareness about inherited Alzheimer's and dementia in general. This October she will be taking part in research that aims to find a way to slow the progression of her rare type of dementia.

There are three genes that, if inherited, lead to the development of early onset Alzheimer's disease. One is this mutated form of presenilin-1, and another is a mutation of presenilin-2. The third is a mutated version of a gene called APP.

All of these genes are related to the production of the protein amyloid, which builds up to form plaques in the brain during Alzheimer's and is thought to be a cause of the disease. Everybody has versions of these genes, but these particular mutations that lead to this inherited form of Alzheimer's disease exist in a small number of families.

Speaking about the risks of inherited Alzheimer's disease Jess Smith, Research Communications Officer, says,

'This is clearly an awful situation for Liz and her family and it shows the devastating impact these genes can have on the affected families. However, such examples are extremely rare and account for a very small proportion of cases of Alzheimer's disease. It's important to remember that most cases of early onset Alzheimer's disease are not the result of these genes.

'The majority of cases of dementia arise from a very complex variety of factors, of which genetics is just one. If you have a parent with dementia, your risk of developing the condition is only slightly higher. There are things that you can do to reduce your risk of developing dementia, such as taking regular exercise, eating a balanced diet and maintaining normal blood pressure and cholesterol levels.'

Find out more about genetics and dementia.

Further reading