{"id":21307,"date":"2022-12-22T16:58:44","date_gmt":"2022-12-22T15:58:44","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/?post_type=purple_issue&p=21307"},"modified":"2023-01-03T11:23:11","modified_gmt":"2023-01-03T10:23:11","slug":"primer-genetic-testing","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/2022\/12\/22\/primer-genetic-testing\/","title":{"rendered":"Primer: Genetic testing"},"content":{"rendered":"\n

PRIMER: GENETIC TESTING <\/h2>\n\n

What can it tell us about our future health risks, and should we all be getting tested? <\/strong><\/h4>\n\n
\"\"
A genetic test taken for a TV programme revealed the actor Chris Hemsworth has a higher risk of developing Alzheimer\u2019s disease <\/figcaption><\/figure>\n\n

Actor Chris Hemsworth, who you might know as Thor in the Marvel Cinematic Universe, recently announced that he was taking a break from the limelight after carrying out a genetic test that highlighted he had a heightened risk of developing Alzheimer\u2019s disease. To find out whether we all ought to be considering testing ourselves, we spoke to Sir Peter Donnelly, CEO and co-founder of Genomics PLC, and emeritus professor of statistical science at the University of Oxford, about what genetic screening can tell us about our health. <\/p>\n\n

WHAT HAPPENS WHEN SOMEONE TAKES A GENETIC TEST?<\/span><\/h5>\n\n

Usually, the test would involve taking a biological sample from the individual. Typically, that\u2019s either a blood sample, or a saliva sample. Then the sample would be sent to a laboratory, which would extract the DNA and then analyse it for the piece of genetic information that the test is trying to find. <\/span><\/p>\n\n

WHAT IS DNA?<\/h5>\n\n

DNA is the chemical material that contains all of the information our cells use to do their stuff \u2013 to make the proteins that allow them to function, and to build up tissues and organs. We get one copy of our DNA from our mother and one from our father. The totality of the DNA is called our genome \u2013 that\u2019s just a word for all of the DNA. <\/span><\/p>\n\n

DNA itself is a long chemical made up of different components. You can think of it as a long list and at each position there\u2019s one of four possibilities that happen to start with letters A, G, C or T. In total we get three billion letters of DNA from our mother and three billion letters of DNA from our father. In every cell in our bodies, each of us has six billion letters. <\/p>\n\n

WHAT IS A GENE?<\/h5>\n\n

A gene is a piece of our DNA where the letters contain explicit instructions that help our cells make a protein. They can differ in length. <\/span><\/p>\n\n

A gene might be just a few hundred or thousand DNA letters long, but some genes are much longer. If we look at the totality of our DNA, only about 1 per cent of it is the genes. The rest used to be called \u2018junk DNA\u2019 before we understood what it was doing. <\/p>\n\n

We now understand that it contains other information. For example, information that tells a particular gene when it should be making a protein. All of our cells have all of our genes. There might be a gene that makes a protein that\u2019s really important in the retina, but you absolutely don\u2019t need that protein in your tongue. And so there\u2019s instructions in the DNA that will be able to tell that gene, \u2018I want you to make this protein if you\u2019re sitting in a retina, but not if you\u2019re sitting in the tongue.\u2019 <\/p>\n\n

HOW BIG AN INFLUENCE CAN A SINGLE GENE HAVE ON OUR BODIES?<\/span><\/h5>\n\n

We\u2019ve got about 20,000 genes in total. In Chris Hemsworth\u2019s case, he\u2019s been talking about one particular gene. We know some things about what that gene does, but there are many mysteries \u2013 as there are with lots of human biology. We all have two copies of that gene, one from our mother and one from our father. The issue is that there can be slight differences between the copies. Lots of these differences don\u2019t have <\/span>any effect at all, but some of them can have consequences and sometimes those consequences can be really severe. In conditions like cystic fibrosis, for example, where if you inherit a mutated copy of a gene that doesn\u2019t work the way it\u2019s meant to, you can end up getting really sick. Sometimes, if you have one copy of a gene that doesn\u2019t work, you\u2019re fine. For example, if the one from your mother doesn\u2019t work, but the one from your father is fine.<\/span><\/p>\n\n

HEMSWORTH HAS BEEN TOLD HE\u2019S AROUND 10 TIMES MORE LIKELY TO DEVELOP ALZHEIMER\u2019S DUE TO THIS GENETIC FACTOR. HOW SIGNIFICANT IS THAT? <\/h5>\n\n

There are some diseases where if you inherit the genetic change, you will get sick. There are other examples, and this is one of those, where if you inherit a particular genetic change, you can be <\/span>more likely \u2013 sometimes quite a bit more likely \u2013 to develop the disease.<\/span><\/p>\n\n

\u201cIn Hemsworth\u2019s case, we\u2019re talking about one particular gene. We know some things about what that gene does, but there are many mysteries\u201d <\/p><\/blockquote>\n\n

For most of the common conditions, such as heart disease, diabetes and many of the common cancers, genetics is a big part of the risk. But it\u2019s not just one change or two changes; it\u2019s millions of positions that each contribute a tiny bit to that risk. So Hemsworth\u2019s example is in the middle, where he\u2019s probably about 10 times more likely to develop disease. And although we\u2019re all very aware of diseases like Alzheimer\u2019s, it\u2019s quite rare. So there\u2019s a big difference between relative risk, which is how much more likely you are to get the disease than someone else, and absolute risk, which is about whether you\u2019ll actually get it. So the important point is it doesn\u2019t determine that he will or won\u2019t get the disease. It just increases the risk for him. <\/p>\n\n

WHAT WOULD YOU SAY TO PEOPLE WHO WOULD RATHER NOT KNOW ABOUT THEIR POTENTIAL GENETIC RISK FACTORS?<\/h5>\n\n

It depends on the disease and on how big the impact is. In the case of Alzheimer\u2019s disease, the gene that was checked for Hemsworth is called APOE and it has quite a big impact on his risk of getting the disease. At the moment, there\u2019s not much you can do about it, so I think different people will take different views. Some would rather know and some would rather not know, and that\u2019s absolutely up to the individual. But I think Alzheimer\u2019s research is progressing really quickly. So it might well be the case that, before too long, there might be things you could do and drugs you could take to help reduce the risk or slow its progression. I think that it\u2019s a slightly different question for different diseases. <\/span><\/p>\n\n

WILL WE EVER SEE A DAY WHERE WE HAVE ENTIRE POPULATIONS ROUTINELY HAVING GENETIC TESTS LIKE THESE?<\/h5>\n\n

I think that will happen. First of all, it should be up to the individual. No one should be forcing people to have tests like this. But for most common diseases, genetics is a risk factor and if we knew about it, instead of just saying: \u2018here are the 10 or 20 diseases you should be most worried about and here\u2019s some generic advice\u2019, we could be saying: \u2018in your case, you\u2019re at particularly high risk of heart disease\u2019. We can actually tell you this when you\u2019re in your 20s, so you should work even harder on diet and lifestyle, or maybe it would be appropriate to go on drugs to reduce your cholesterol a bit earlier in life. We could do that because we have that special information about you. <\/span><\/p>\n\n

\"\"<\/figure><\/div>\n\n

SIR PETER DONNELLY <\/strong>Peter is an emeritus professor of statistical science and director of the Wellcome Trust Centre for Human Genetics at the University of Oxford. He is also the CEO of Genomics PLC. <\/em><\/p>\n\n

<\/div>\n\n

IMAGE: GETTY IMAGES<\/p>\n","protected":false},"excerpt":{"rendered":"

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