A beginner’s guide to genetic studies

One of the aims of the NCMH is to increase our understanding of mental health problems by looking at genetic risks. But why are genetics in mental health important and how do we study them?

Genetics and mental health

For many decades now, research studies have been repeatedly and consistently finding that nearly all mental health problems run in families. All the evidence points to the conclusion that having a parent, sibling or even a more distant relative (such as an aunt/uncle or grandparent) affected with a mental illness increases a person’s chances to also have a mental illness.

That said, we also know that having a relative with mental health problems does not always mean that family members will also have problems. Mental health problems are complicated.

A person’s experiences can also be involved in increasing or even decreasing the risk of mental illness, and we are also conducting psychological and social research to learn more about this area.

We also know that when genetic factors are important, it isn’t just one single gene that causes a mental illness. Studies show that thousands of genes and other types of genetic factors are involved in mental illness in a complex way.

For a well-written and clear explanation of this complex process, see this great post by Professor Marcus Munafo from the University of Bristol.

Family and genetic research is an important clue for our understanding of the causes of mental health problems. Given how much suffering such problems can cause, we need to understand the genetics to help affected individuals. A better understanding of the genetics and biology of a mental illness is likely to lead to future treatments and therapies for patients. It is also likely to lead to better and faster diagnosis of mental illness.

Genetics: the very basics

Our genetic information is stored in the cells of our body in long chains known as DNA. Our DNA is made up of many molecules, including cytosine, guanine, adenine, and thymine. These 4 molecules are known as nucleotides and are referred to by their letters: C, G, A and T. The order of these letters is each person’s genetic profile, or “genome”.

Many sections of a person’s genetic profile will be identical to that of every other person. Sometimes, a small group of people will have a different letter in a part of their genetic profile when compared to the profiles of most other people. Such genetic differences are known as rare “variants”. For other parts of our genetic profiles, there are more common variants – for example, half of a group of people might have a G at a specific part of the human genome and the other half might have a T instead.

Genes (the parts of DNA that make proteins) are made up of many thousands of such letters. However, genes make up only a part our DNA. There is a lot of DNA in between genes that is involved in complicated functions, such as controlling which genes will make proteins, how much and in which cells in the body.

In humans, DNA is separated into 23 pairs of chromosomes. One chromosome in each pair is passed on from your mother and one from your father. Most of your DNA is inherited like this. But sometimes, small new changes happen during early development, which mean that some small fragments of your DNA are unique to you and will not be present in your parents or siblings. These are known as “de novo” variants.

How do we use genetic information to study mental health difficulties?

Two test tubes containing blood samples being held up by somebody wearing blue gloves

After volunteers have given a blood or saliva sample, the DNA is extracted and genotyped in the lab, and each person’s genetic profile is uploaded to a computer database. We then compare specific genetic variants in volunteers who have a particular mental health problem (such as schizophrenia or ADHD) to the genetic profile of healthy volunteers. If the group with mental health problems has more or less of a particular genetic variant than the healthy group, this is evidence for a relationship between that genetic variant and the mental health problem.

Of course, DNA is quite complex and so there are tens of thousands of genes, millions of single genetic variants and many other types of genetic changes we might want to look at. Some of the genetic changes are not very common. Because of this, we need a lot of volunteers to help with this research. The more volunteers are in a study, the higher our confidence to find the genetic variants related to a specific mental health problem.

For example, when a study led by NCMH Principal Investigator Professor Mick O’Donovan found more than 100 genetic variants linked to schizophrenia, researchers examined over 80,000 samples. When we do find such genetic variants involved in a mental illness, this information can be used in further research studies to help us understand the biology of a mental illness.

Genetic research is a very important and growing area, which has a lot of potential to help many patients in Wales and around the world.

Dr Joanna Martin

Dr Joanna Martin is a Sir Henry Wellcome Postdoctoral Fellow researching genetic risks for neurodevelopmental disorders including ADHD and autism spectrum disorder, with a particular focus on differences in females and males affected by these conditions.

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