If you have been living on Earth recently, you’ll have come across the news that a certain Hollywood actress has undergone major preventative surgery due to the discovery of a faulty gene. The gene in question is called BRCA1 and, if mutated in a certain way, it is known to greatly increase a carrier’s chances of developing breast cancer. This incident has thrust genetic screening into the limelight – but how useful is it to know the secrets concealed within your genes?
We now have technology to take screening even further. Writer and journalist Carole Cadwalladr reports in the Guardian that whole-genome screening by Illumina is now available for just $5,000. That may seem a lot, but considering it would have cost $2.7 bn just 10 years ago, it’s a hell of a price cut. Several other companies, including 23andme and AncestryDNA are also offering to screen your genome and let you know what, if any, potential disease-causing mutations you have. Some of these scans cost as little as $99.
But do you really want to know what, if anything, is wrong with your genes? In some circumstances screening can be very useful – it can save lives. When Angelina Jolie tested positive for the BRCA1 mutation, she took the decision to have a preventative mastectomy. She hopes this will allow her to avoiding the pain of cancer and the pain her children would face watching their mother suffer; a pain she herself knows all too well. In cases like this, screening and early intervention is important because we know that a mastectomy can greatly reduce a carrier’s chances of developing the disease.
Photo: Ajsmen91, commons.wikimedia.org
But what if there is no prevention for the disease detected by the sequencing? One of the more famous examples of this is Huntington’s Disease. Huntington’s is a debilitating degenerative disorder characterised by shaky, jerky movements (called chorea) and progressive cognitive decline. It is caused by a single faulty gene, huntingtin. This gene is inherited in a dominant fashion, meaning that if one of your parents has the disease, you have at least a 50% chance of also suffering. As sufferers do not generally start to show symptoms until their 40s, they may not realise they carry this mutation until after having children – who will therefore also be at risk. It is now possible to screen people for the faulty huntingtin gene. However, there is no cure for Huntington’s. Knowing you have the gene will not help you to prevent the onset of disease; therefore do you want to know? This is a dilemma that many children of Huntington’s sufferers face. Some decide it’s best to know, especially if it will influence their choice to have children, but others would prefer not to have this time-bomb ticking over their heads.
Genome screening could allow people to adjust their lifestyle to counteract a faulty gene. For example, it is common knowledge that smoking can cause lung cancer. However, everyone also seems to have a great-aunt Gladys who smoked 90 a day and died at 102 after getting hit by a bus. On the flip side, there are people like the Record Breakers presenter Roy Castle, who died of lung cancer despite being a non-smoker. It may be that your genes determine whether you are more like Gladys or Roy. If you get your genome screened and it turns out you’re more like Roy, you could adjust your lifestyle accordingly and quit (or not start) smoking.
I’m also going to use a personal example here. If you are familiar with this blog, you may know that there is a history of Alzheimer’s Disease and dementia in both sides of my family. The cause of Alzheimer’s disease is so far not clear-cut; it appears to be a mixture of genetic and environmental factors but nothing is known for sure. One of the strongest genetic links so far is a gene called ApoE. If you have a version of the gene called ApoE4 you are at higher risk of developing Alzheimer’s. However, it does not necessarily mean that you will suffer from the disease.
Photo: Humbads, commons.wikimedia.org
So let’s say, hypothetically, that I had my genome screened and it confirmed I had the ApoE4 gene. What can I do with this information? Well, the first thing I’d probably do is panic. I’ve seen Alzheimer’s disease happen and don’t really wish to go through that. However, I am now prepared. I am at higher risk; therefore I need to try and counteract that risk. There are several methods which have been suggested to reduce the risk of Alzheimer’s disease, including eating curcumin, a spice found in curry, and keeping the brain active by doing crosswords or learning a musical instrument. I could also avoid sugary foods, as there is increasing evidence of a link between diabetes and Alzheimer’s disease. So now I’m more informed, I can happily shovel spoonfuls of chicken tikka masala into my mouth with one hand whilst playing the piano with the other and hopefully I won’t get Alzheimer’s.
But there’s another side to this. If I have the faulty gene, I will probably have inherited it from at least one of my parents. Which one? Should they get screened too? What if it’s too late for them to take preventative measures and now all they know is that at some point they might get dementia? What happens if I have children? Should they be screened? How early on do you need to start taking preventative action? What if the screen flags up another faulty gene? Or several? What if I can’t prevent a disease caused by these other faulty genes and so will have to go through life knowing that I will at some point suffer from it?
As this is a whole-genome screen, as opposed to a screen for one particular gene, it is also likely to pick up genes that you weren’t even aware you carried. Some mutations are carried silently through families, or your DNA may have become mutated another way, e.g. through smoking or exposure to UV light. Do you want to know that you may at risk of a disease you may never even have heard of? Again, good if it’s preventable (for example you discover an allergy to a medicine that you haven’t yet had to take) but if it’s not preventable, what does that leave you with? That ticking clock over your head.
The other issue here is how this type of information will be used. Illumina loads the data onto an iPhone app for you, meaning that the data must be stored somewhere. Who else has access to that information? How secure is it? Could it be possible in the future that people start demanding to know the results of genome screens for potential prime ministers to make sure they’re not going to suddenly get cancer whilst they’re supposed to be running the county? And what if health insurance companies start demanding full-genome screens before you can get a policy?
Also, new genetic links to diseases are being discovered all the time. So a screen done now may miss a genetic mutation that is flagged up in the future as being a possible cause for disease. Would you have to get screened more than once? Maybe you’ll need to be screened every few years to keep up with discoveries being made.
I feel I should point out here that the science behind this technology is amazing. The fact that it is even possible is a huge achievement and a testament to the dedication and innovation of the scientists who developed it. And it was invented to help people – to screen for faulty genes with the idea of saving lives. I have worked in a lab which has collaborated with Illumina and in doing so the lab was able to identify a new Alzheimer’s risk gene (the catchily named PCDH11X). This is all useful and helpful information. However, my worry is that the information will be exploited by other people looking for a profit, or preying on people’s fears, as unfortunately these things so often are.
A coin showing your ancestor, Charlemagne
Photo: Fallschirmjäger, commons.wikimedia.org
But what about if you’re having your genome screened to discover the secrets of your ancestry? This was done recently for Prince William, and the papers excitedly claimed that “he will be the first king of England to have a genetic link to India“. However, using these services to find your ancestry may be interesting but it is not always accurate. As explained by this Sense About Science leaflet, genetic screening is not an exact science. Also, when you’re told that you are related to Charlemagne, well, so is everybody else alive today (according to an episode of QI, anyway). Most genetic ancestry screens will only go via one line – either your mother’s, through mitochondrial DNA, or your father’s, through the Y chromosome line. This leaves out an awful lot of your other potential ancestors, for example your maternal grandfather or paternal grandmother. These screens do not, and probably cannot, tell you the whole story of your ancestry.
Is it a good idea to re-open Pandora’s Box, especially if you’re just curious about your genes? Will it save millions of lives or lead to a weird state where everyone has to know exactly what disease they may or may not suffer from at a given point in time? I think, like the people at risk of Huntington’s, and like Angelina, it’s a personal choice. Some people are happier not knowing, some will want or need to know. No one should ever be forced to have their genome screened. Measures also need to be taken to make sure that this information stays personal and secure. I’m nervous about the idea that what your genes hold may become public knowledge. I personally don’t think I want to know what’s in my genes. I am already aware that I am at risk of developing Alzheimer’s, and there’s no harm in taking preventative measures anyway. I do like a good curry.
Post by: Louise Walker