8 May 2022

Prof Andrew Shelling on how genetic testing helps predict disease

From Smart Talk, 7:05 pm on 8 May 2022

The ability of genetics to predict both human disease and behaviour is an exciting and constantly evolving field, however, it’s important to sort fact from fiction when it comes to ‘blaming your genes’.

In this talk, medical researcher Andrew Shelling covers the red herrings of genetic research and explains where advances are really being made.

From Raising the Bar - Home edition 2022

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Photo: AFP

Edited highlights from the discussion

The world of lifestyle genetics is a very murky one.

There are a whole lot of things that are not diseases but traits, like baldness, food preference, freckles, or addiction, which now have genes associated with them.

Companies have been going direct to consumers asking them to spit into a tube and get information about these genes. Often these types of genetic tests target the worried well, especially through social media.

One of the controversial ones that’s popped up over the last few years is the gay gene. People have gone looking for it. A recent study that came out just a few years ago, published in a really good journal, studying large numbers of people found only five hits. So there’s no gay gene. Instead, there are some weak associations. One of them was related to the sense of smell. And one of the other associations was with male pattern baldness, which again speaks to some sort of hormone interaction.

people, homosexuality, same-sex marriage, gay and love concept - close up of happy lesbian couple holding hands over rainbow flag background

Photo: 123RF

Some lifestyle genetics have been exploited by different companies that are going direct to consumers. I refer to these as genetic horoscopes: they may be interesting, they may be real, but they are not always based on robust science.

So, we’ll move now to the claim that genetics could predict the age that you lose your virginity. At face value, this seems sensational. But if you really were to think about it, the age at puberty is very well-defined event in people’s lives.

If you go back 200 years people went through puberty aged 18 or 19, now aged 12 or 13. There are clearly some factors that are at play there, probably related to good health and body weight that’ll allow puberty to happen earlier. By contrast, the age at which menopause begins is fixed; it hasn’t changed for thousands of years.

So what this study was really doing in asking nearly 400,000 people about what age they lost their virginity, –which is probably a marker for puberty – was establishing a few hundred gene variants that seemed to be clearly associated.

Some of them were related to reproductive factors (eg hormone levels), and some with behavioural and psychiatric traits such as risk seeking-behaviour, sociability, and ADHD. Some of the things they found sound really interesting to an academic like me, but still aren’t terribly important. These findings are not diagnostic. You’ll never be able to reliably predict by gene tests the age that you’re going to lose your virginity at. It’s just fun and interesting.

I’ll finish by giving two examples about nature versus nurture.

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Photo: 123RF

I read in the notable medical journal the NZ Herald several years ago that if you have both parents that smoke you’ve got a 25% chance of smoking yourself. If only one parent smokes, you only have an 11% chance, if no parents smokes only a 4% chance.

So doesn’t that make you think, “Oh my goodness, you just copy what your parents do and that familial influence dictates your behaviour. Surely this lands firmly in the area of nurture?” However, since that article appeared, gene variants have been found in a gene called CYP2A6 related to nicotine metabolism. It seems very clear that based on their genetics, some individuals find cigarette smoking much more enjoyable, and a lot harder to give up. So I would argue that even though it looks like it’s all nurture, there is always going to be a genetic influence.

My final example – showing how genetics is sometimes over-hyped – was a very interesting study done a few years ago, looking at Japanese who moved from Japan to Hawaii. And what they found was that in two generations, a doubling in breast cancer, and for stomach cancer, they saw the exact opposite, a halving.

You can’t argue that genetics is at play in that example because it doesn’t change in one or two generations. Instead, it probably shows that there is always some influence from the environment. We know that moving away from a soy-based diet may limit the role of phytoestrogens that seem to be protective against breast cancer. With stomach cancer there’s possibility of H. pylori, a bacteria in the stomach, reducing because of the move to a different country.

Graphic of Andrew Shelling

Photo: University of Auckland

About the speaker

Andrew Shelling

Professor Shelling is Associate Dean (Research) at the Faculty of Medical and Health Sciences, and Acting Director for the Centre for Cancer Research. His research is primarily interested in understanding the molecular changes that occur during the development of genetic disorders, focusing on breast and gynaecological cancer, and reproductive disorders

Raising the Bar is presented in association with the University of Auckland


Photo: University of Auckland