Medicine Gets Personal: Understanding Genome-Wide Association Studies

Jennifer Payandeh
24 July 2017

Above: Image © Ca-ssis, iStockphoto.com

What can your genes tell you about yourself?

Alleles are different variants of genes. They indicate what kinds of physical traits you have. For example, everyone has a gene for eye and hair colour. But I may have the alleles for blue eyes and brown hair while you may have the alleles for brown eyes and blonde hair.

But scientists have learned that your genes have information about all kinds of qualities, even some of your less obvious ones. For example, your genes determine if you’re lactose intolerant, how fast you break down caffeine, and even the consistency of your earwax! They can also determine how likely you are to develop complex diseases like diabetes and Crohn’s disease. These fascinating findings are all due to Genome-Wide Association Studies (GWAS). And they just might give doctors a new, personalized way to treat disease in the future.

The history of GWAS

Before we talk about GWAS, let’s look at some important work and discoveries that came first. The Human Genome Project was an international research program that mapped out the human genome (the complete set of human DNA). Completed in 2003, it helped scientists understand the organization and function of all human genes.

Also, scientists have discovered that the most common type of genetic variation between people is called a single nucleotide polymorphism (also known as an SNP or “snip”). SNPs work like markers in your DNA, indicating the location of nearby genes.

The building blocks of DNA are called nucleotides. Most alleles consist of several nucleotides together. SNPs only consist of a single one, so they’re much smaller than other alleles.

Nucleotides are made up of many chemical components, including one called a nitrogenous base. That’s what scientists use to differentiate one type of nucleotide from another. There are four different types: adenine, cytosine, guanine, and thymine.

Some people might have an adenine at a certain position, while others might have a guanine. That’s an example of an SNP.

What is a GWAS?

In a GWAS, scientists scan the entire genomes of groups of people to look for SNPs. They then analyze the SNPs and look for patterns between groups of individuals. The goal is to see whether a certain SNP can be reliably associated with a group of people that share the same phenotype, or observable characteristics.

For example, scientists found that an SNP in a particular position in a particular gene can determine what your earwax is like. If you have an adenine in that position, your earwax is dry. If you have a guanine, your earwax is wet!

As of 2011, scientists have done over 800 of these studies! GWAS have found SNPs associated with a wide variety of populations. Combining results from studies allows scientists to better understand the structure and the function of the human genome.

So how do scientists perform a GWAS?

Did you know? As of 2008, 3.1 million different SNPs have been identified in the human genome!

First, scientists must assemble a group of people who have the characteristic they want to study. Then, they have to find people who don’t have that characteristic, but have other similar characteristics. These people make up the control group.

For example, let’s say scientists want to study people with diabetes. They might assemble participants with diabetes from a particular ethnic group. Then they would assemble people from that same ethnic group who don’t have diabetes. That would be their control group.

It’s important to have a control group with similar characteristics to the group being studied. That way, it’s more likely that any differences the scientists find will be due to the characteristic being studied (in this case, diabetes) than another factor.

Once these two groups are in place, the scientists must analyze the participants’ DNA. They usually get this from a saliva or blood sample and place it on tiny chips. Machines in the lab scan through the entire genome of each participant from both groups and look for SNPs.

Then, the scientists analyze the data. They may find one or more SNPs that everyone (or almost everyone) in the diabetic group has and nobody in the control group has. This could mean that these SNPs contribute to a person getting diabetes.

Sometimes, a GWAS might get different results the second time scientists run it. In these cases, the SNPs might not actually cause a disease. They could just be “tagging along” with the disease-causing SNP. When this happens, scientists may run more complex studies to understand what’s going on.

GWAS and medicine

In the future, doctors may be able to design a specific medical care plan for you based on your alleles. For example, if you have an SNP associated with a certain disease, your doctor can offer preventative treatment. They might also be able to tell how you will respond to certain medications before you take them. This is called personalized medicine. It’s still in its early stages, but could lead to a very exciting, more efficient approach to keeping you healthy!

Did you know? GWAS studies have found SNPs associated with some people’s resistance to certain viral infections!

How do the results of GWAS impact you today?

Want to learn more about yourself? Companies like 23andme and deCODE Genetics can give you all kinds of information about your genes, like where your ancestors came from or what percentage of your SNPs you inherited from Neanderthals. All of this information comes from GWAS results. You can see just how wide the applications of GWAS can be!

Learn more!

What are genome-wide association studies? (2017)
Genetics Home Reference

Genome-Wide Association Studies (2015)
National Human Genome Research Institute

SNP (2014)
Nature Education

Personalized medicine: progress and promise (2011)
I.S. Chan & G.S. Ginsburg, Annu Rev Genomics Hum Genet. 12

Jennifer Payandeh

I just completed my undergraduate degree in Health Sciences and Psychology at Simon Fraser University in Burnaby, BC. I have been a volunteer at the SFU chapter of Let’s Talk Science for the past 2 years, and my favourite moments are when students tell me they want to study science when they grow up! My interests include genetics, astrobiology, medicine, and cats. On weekends, you can find me hiking around the many beautiful trails of BC! Find me on twitter @jenpayandeh.