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Genetics (Part 2)

Genome research studies have helped us identify specific components that act as risk factors in our genes. Dr Chris Jones explains more in this video.
From the publication of the first draft of the human genome sequence in 2004 to the technological advances that have drastically reduced the cost and the time that it takes now to sequence DNA. Our increase in the knowledge of DNA has allowed us to annotate the human genome sequence extensively. The pace of change in our knowledge has been truly drastic. So there is a genetic elementto cardiovascular disease. And we can read the genetic variation in an individual’s genetic code. So we should be able to design an experiment to work out that the association, the link, between those genetic variants and the risk of getting disease.
In other words, we should be able to work out what the genetic risk factors for cardiovascular disease. And we can, but first, let me explain what we mean by genetic risk factors. Genetic variants exist between all of us. These are changes at a genetic level that alter the proteins that are transcribed from our genetic code. These could be changes that alter the function of a protein. Change how efficiently it operates. These could be changes that alter how much of a protein is transcribed. Or even when it’s transcribed or where it’s transcribed. These genetic differences may only exist in you or perhaps, within your family or perhaps, in the number of families around the world. And we call these private changes.
They could also exist in 1 in 100,000 people or 1 in 1 million people. We tend to call these rare. Or they could be common throughout the entire population. There are roughly, very roughly, about 10 million variants in each of us. But which of these variants is causing the risk of cardiovascular disease? There are two main experiments that we can do to work this out. The first is a linkage study. For this, you need a large family cohort. And you link the transmission of a genetic variant with the cardiovascular disease as it develops in family members. These types of study have been particularly successful in unearthing the private genetic variants. The other type of study is an association study.
For this type of study, we recruit large numbers of subjects. Cases and controls. So the cases are subjects who have cardiovascular disease. The controls are subjects without cardiovascular disease. We then look to see where the genetic variant is distributed within these two populations. So is a genetic variant more prevalent in the cases or the controls? Because of our advances in our knowledge and our ability to perform genetic studies and our ability to understand genetic variation and measure it over the recent decades, it’s now possible to measure hundreds of thousands, if not millions of genetic variants simultaneously. If we use this technology in an association study, we call this a genome-wide association study.
In essence, we’re performing an association study over the whole genome simultaneously. Since 2007, a number of these type of studies have been performed. The latest was reported in 2013 by the Cardiogram Consortium. This study took 61,000 cases. So 61,000 people with cardiovascular disease. And 131,000 people without cardiovascular disease. And they identified 46 genetic variants that were linked to the risk of developing cardiovascular disease. These types of studies are very good at unearthing common genetic variants. But have so far only identified variants that account for a very small proportion of the total inherited component of cardiovascular disease. And the variants they have discovered are usually related to controlling lipid level or blood pressure.
So there clearly is an awful lot of work we still need to do, but we are starting to unravel the genetic components, the genetics that underlying cardiovascular disease.

Dr Chris Jones continues to explore genetics as a non-modifiable risk factor by looking at some of the studies made in genome research that have helped us identify specific components that act as risk factors in our genes.

You can download the Week 4 supplement, which contains additional images and descriptions to help you understand the topics covered in this video.

British Heart Foundation resources

Find out more in the following, optional, video Family history and heart disease; one of a series, produced by the British Heart Foundation Risking it: Fighting against risk factors in coronary heart disease.

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Heart Health: A Beginner's Guide to Cardiovascular Disease

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