If Something is “Genetic” it Can Still be Influenced by the Environment

Learning that a disorder is influenced by your genes can be a frightening and confusing experience. People may think that because your DNA doesn’t change, it also means that we can’t do anything about “genetic” disorders. Meg and Kirstin [EDIT lab PhD students] explain how the environment and genes can work together to change the course of disorders.

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Many people have probably heard the phrase “the nature nurture debate”, usually when talking about the origins of human behaviour or psychology. The troublesome thing about this phrase is that it pitches “nature” (or genes) against “nurture” (the environment, which includes parenting and life events). It makes it seem as if only one or the other can lead to any given outcome. This assumption might be mostly valid for a lot of things. For example, imagine a nature v nurture scorecard for some relatively straightforward traits:

                                                        Nature      Nurture

I have a South African accent                            |

My eyes are green                          |

I have a weird left toe *                 |

I have a weird left toe **                                    |

*Because I was born with it

**Because I dropped something really heavy on it when I was young (and let’s not get into how much of this is due to a genetic propensity to clumsiness!)

But what happens to that scorecard when we add more complex traits?

                                                        Nature      Nurture

I’m good at school                                     ?

I sometimes struggle to sleep                 ??

I’m scared of flying                                   ???

Therapy really works for me                  ????

We now know that for most traits, nature and nurture work together. Just because your DNA cannot change does not mean that the way it is expressed or the role it plays is unalterable. One of the key determinants of how your DNA comes to play a role in who you are (your traits, thoughts and behaviours) is the environment. As a research group, we are interested in mental health disorders that are influenced by many genes, as well as the environment. To make it easier to think about exactly how the environment can have an effect, let’s use an example of a simple single gene disorder where the environment has a direct influence.

Phenylketonuria (PKU) is a rare inherited metabolic disorder affecting the metabolism of the amino acid phenylalanine. In the past, individuals born with the single gene mutation that causes PKU would develop intellectual disabilities, mental and behavioural disorders, to the extent that some adults with untreated PKU are unable to speak or walk. But these severe impairments can be completely avoided through an environmental modification – a special diet. Since the 1960s it has been standard to check for PKU in newborns via the ‘heel-prick test’. A baby that screens positive for PKU can be put on a modified life-long diet of low-phenylalanine foods and supplements, which allows them to develop typically. This is why you may have seen warnings on products like chewing gum and diet drinks, which contain phenylalanine.

Short-sightedness, or myopia, is a highly heritable trait (e.g. Teikari et al., 1988), which provides another clear (pun intended) example of an environmental intervention having an effect on a partially genetic trait – glasses!

Hopefully these examples clearly demonstrate how the environment or “nurture” can influence a trait or illness that is primarily thought of as “genetic”. Unlike PKU, mental health problems such such as depression and anxiety are not caused by a single gene, but by a vast number of genetic variants. Whilst individually these have small effects, cumulatively they have a significant influence, acting alongside and in combination with environmental factors. By discovering genetic variants that increase the likelihood of developing a mental illness, and what environmental factors interact with those variants, we can develop environmental interventions for treatment or prevention. For depression and anxiety, these could include having a supportive social network, psychological therapy, sleep and exercise.