In the news: The genetics of Alzheimer’s risk
By Dr Laura Phipps | Sunday 27 October 2013
The study is unique in the field of Alzheimer’s, not just for the sheer quantity of genetic information it has produced but for the huge amount of teamwork needed to pull it off.
Let’s look at these new findings in context.
How ‘genetic’ is Alzheimer’s?
Only very rare cases (around 1%) of Alzheimer’s are directly inherited from parent to child, usually affecting people in their 40s or 50s.
The most common form of the disease is called late-onset Alzheimer’s, affecting people over 65, and has a range of risk factors – age, genetics, and lifestyle.
What are Alzheimer’s risk genes?
The exact DNA code that makes up each of our genes varies naturally across the population. Often this variation has no effect on us, but scientists are finding that some of these genetic changes or ‘variants’ are linked to a higher risk of Alzheimer’s. Scientists have been working hard to identify genes that harbour variants linked to Alzheimer’s because these genes implicate biological pathways in the disease that could yield new treatment targets.
In most cases, having a risky version of a particular gene may only make us slightly more likely to develop Alzheimer’s – perhaps 1.2 fold more than someone with a neutral version. However, if we have a few of these risk genes, their effects may start to add up.
What do we know already about Alzheimer’s risk genes?
Before today, 11 genes had been linked to an altered risk of Alzheimer’s disease. Over the past four years, your donations to Alzheimer’s Research UK have helped to fund the discovery of eight of these.
Hover over the image below to find out what we know about these genes.
Joining forces for a common good
To look for new genetic variants associated with Alzheimer’s risk, researchers have been conducting Genome Wide Association Studies. In these studies, scientists compare the DNA code between people with and without Alzheimer’s, looking for subtle changes in the sequence that are more common in people with the disease.
Then, they try to pinpoint the exact genes these variants sit within, and look at what biological processes these genes control.
One obstacle to identifying genetic variants that only carry a very low risk of the disease is that it can be hard to tease out the true signals from background noise. To overcome this problem, more than 180 researchers from across 15 countries offered up data from the samples they had been using in their own genetic studies.
This huge collaboration allowed data from more than 25,000 people with Alzheimer’s and 48,000 people without the disease to be compared – the largest ever study of its kind in Alzheimer’s disease.
11 new genes
Analysing the data from this study has taken more than two years, but has thrown up some exciting new findings. Reassuringly this ‘über-analysis’ has confirmed almost all of the genes that had been previously linked to the disease (this kind of validation is a vital part of adding greater certainty to the scientific process).
But the study has also identified 11 new regions of the genome that could harbour genetic variants linked to the disease. While it can be hard from these studies to pinpoint the exact culprit genes, the scientists are closing in on their targets.
What does this mean for people with Alzheimer’s?
The value of identifying these new Alzheimer’s risk genes does not lie in their potential to identify people at risk or aid diagnosis, because each variant only confers a small risk. That means that people who carry one of these risky genes may still never go on to develop Alzheimer’s and vice versa.
The true potential comes from understanding what all of these genes do and from that, highlighting new avenues for investigation to understand what is causing or driving Alzheimer’s. It is from this understanding that we can build a detailed picture of the disease and identify targets for the development of new treatments.
Today’s findings have implicated a range of biological processes that could be important in the disease, including:
- The immune system and inflammation
- The control of cell movement
- The transport of molecules between cells
- Cell-to-cell communication
- The cellular scaffolding that helps maintain structure and direct the transport of cargo within cells.
As our Director of Research, Dr Eric Karran said: “The true value will come from pinpointing the exact genes involved, how they contribute to Alzheimer’s, and how this could be translated into benefits for people living with the disease.”