The Naked Science of a DNA test

I had my genes sequenced by 23andMe in the name of science… and of course I had to ask about the ‘maths’ behind the results.

Nowadays, a lot of companies offer online ancestry tests, or tests to quantify your risk of inheriting some life-changing diseases. But how seriously should we take their results? Izzie Clarke and Tom Crawford spoke to Garrett Hellenthal from UCL and Julianna Cintron from 23andMe in order to find out…

Tom – Fill the tube with saliva to the black wavy line… shall we just crack on?

Izzie – Okay! You get the idea. But in order for companies to analyse our genetic information, all we have to do is spit into a test tube and send it off to the lab. Tom sent his to a company called 23&Me to find out about his health and physical traits, and I wanted to explore my family history. So, how does a bit of my saliva reveal so much about my ancestry?

Garrett Hellenthal from University College London’s Genetics Institute…

  • Saliva contains your genetic code in a series of cells which can be extracted and identified via a series of genetic markers that define your unique DNA sequence.
  • They look at about 500,000 different pieces of genetic code and compare them to the codes of people in the company database to determine who you share matching DNA patterns with.
  • Izzie found out that she is 30% Irish, 24% Western European, 15% Great Britain and 15% Scandinavian.

Izzie – But what about health and physical appearance? Let’s take a look at Tom’s results…

Tom – I think most of them are correct for me like I should likely have lighter eyes, and I have blue eyes. It says likely little upper back hair, and I can fortunately report I have minimal upper back hair. I was also pleased to see that I’m likely not to have a bald spot; I really hope that one’s true.

Izzie – In addition to appearance, Tom’s test was able to look at specific parts of his genetic code and explain the likelihood of there being a change called a ‘variant’, which could possibly lead to a life-changing illness.

Julianna – My name is Julianna Cintron and I’m a produce specialist on the customer care team at 23andMe.

  • There are some traits that are more influenced by genes than others, for example if you have two copies of the gene associated with having red hair then you are much more likely to have red hair.

Tom – Just with you mentioning there this idea of it’s to do with the confidence in something, or there’s a probability. We’re using phrases like more likely, it’s not sort of fixed. In my result I was told that I have a particular variant which leads me to be at a higher risk of Alzheimer’s disease and I was just wondering what exactly does this mean? Does this mean I will get Alzheimer’s; does this just mean I’m above average likely; how does this result actually relate to the risk factor?

  • The e4 variant is known to impact your risk of developing Alzheimer’s and having one copy of the variant puts you at a slightly increased risk of developing Alzheimer’s by a certain age. Having two copies increases the risk further.
  • Most of the genetic risks are actually relatively small, much less than say smoking or unhealthy lifestyles in general.
  • The most important thing is to use the results as ‘one piece of the puzzle’ and not as a diagnosis that you will or will not get a certain disease.

You can listen to the full interview with the Naked Scientists here.

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