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Genes and mental illness

In a few months I will be a psychologist working with mental health. That seems pretty far from genes in cells, right? It turns out genes are profoundly important to our mental health and the purpose of this post is to give an overview of the topic.

The relationship between genes and mental illness is complex. Researchers call the relationship non-deterministic and subtle. Genes do not tell us exactly who will have a certain disorder and who will not. It is also extremely hard to predict who will later develop mental illness. There may or may not be any signs during development. Nevertheless, this is a ”hot” research topic that has the potential to completely transform our understanding of mental illness.

For adult-onset common psychiatric disorders in particular, development is often within normal limits1

Genes as a risk for mental illness

The interplay between genes (nature) and environment (nurture) has generated debate and controversy for centuries. Most mental illnesses have at least 50 % heritability, which means that genes account for about half of the variation in the population2. This varies quite a lot between individuals. For example, if your family has a history of mental illness, the influence of genes is likely to be higher. It is lower if you don’t have a family history of mental illness but experience bullying or severe neglect as a child.

The genetic architecture for common mental illnesses like OCD consists of many genes that each has a small effect. It is unlikely that we will find a single gene that causes OCD, depression, or any other common mental illness. It will probably be more like 100-200 different genes3. This will help us to understand what OCD is and will keep researchers occupied for a while4. But in order to have implications for clinical practice, we need something simple. This is where polygenic scores become important. Essentially, it is a summary of an individual’s genetic risk for a disease or other outcome. Researchers are now starting to investigate the relationship between polygenic scores and a variety of outcomes, for example educational achievement5, first-episode psychosis6, and obsessive-compulsive symptoms in the general population7. This will not only improve our understanding of complex phenomena, but may also point to effective prevention and treatment strategies.

Using polygenic scores to predict treatment outcomes

Polygenic scores may help us understand which treatment works for whom, and why. CBT for OCD is effective for about 60-70 % of patients. It’s quite remarkable that we are able to influence such a complicated phenomenon in just 14 weeks of treatment. Nevertheless, this also means that 40 % of patients do not benefit from treatment. There is still much to be done. In the new field of therapygenetics, researchers are looking for ways to enhance psychological therapies with information from genetic research. Results from the first large-scale effort was published last year8. They found no common genetic variant that had a large effect on response to CBT in children. The researchers concluded:

Future investigations should maximise power to detect single-variant and polygenic effects by using larger, more homogeneous cohorts.

What will happen within the next few years?

We still have a long way to go before this research has real implications for psychological therapies. Even still, I think this is an exciting field with huge potential. True personalised medicine is on the horizon and I hope that it will result in better treatments for individuals with mental illness.

References

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Oskar Flygare
PhD Student in psychology

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