(ORDO NEWS) — Psychiatric disorders, including depression, schizophrenia and anorexia, are linked to biological markers found on routine blood tests, according to our new study of genetic, biochemical and psychiatric data from nearly a million people.
The study will help us better understand the causes of mental illness and possibly help find new treatments.
Healthy body, healthy mind
People often view mental health as separate from the health of the rest of the body. Far from it, there is clear evidence that many of the biochemicals involved in diseases such as diabetes and autoimmune conditions directly affect our brain function.
Many studies have tried to solve this problem by focusing on substances called biomarkers that can be easily measured in the blood.
A biomarker is simply something in the body that is a sign of a specific disease or process. They often refer to things that are listed on a blood test ordered by a doctor, such as cholesterol, blood sugar, liver enzymes, vitamins, or markers of inflammation.
Biomarkers found in a routine blood test are useful because they are often influenced by diet and lifestyle or drug treatment.
The complex role of genetics in mental health
Studying the role of these blood biomarkers in mental illness is often difficult. Many studies in this area are often not large enough to draw serious conclusions.
One solution is to study the genetic influence on both mental illness and substances measured in the blood. Genetics is useful because today we have data from millions of people who have volunteered for research.
Both mental illness and blood biomarkers are what geneticists call “complex traits.” Complex traits involve many genes and are also influenced by environmental factors.
The wide availability of genetic data has allowed us to study how a huge number of tiny changes in the DNA sequence (or “variants”) are associated with the risk of mental illness. These same variants may be associated with measured levels of biomarkers in the blood.
For example, a variant in a certain gene may increase the risk of developing schizophrenia and may also be associated with a decrease in the level of a vitamin circulating in the blood.
Most of these options individually are associated with very small changes, such as the risk of developing a mental illness, but together they can lead to more significant consequences.
How are blood biomarkers related to mental illness?
In our recent study, we tried to use genetics to study the relationship between nine mental disorders and 50 factors measured in a routine blood test, such as cholesterol, vitamins, enzymes, and indicators of inflammation.
We used data from very large studies conducted by other people, which together included data from nearly a million volunteers.
Our study confirms for the first time the existence of a so-called genetic correlation between blood biomarkers and mental illness, which turned out to be more common than previously shown.
Genetic correlation means that the impact of DNA sequence changes on the risk of developing a mental illness and the levels of this biomarker were more similar to each other than what could happen by chance.
To give one example, in our study, there was a positive genetic correlation between white blood cell count and depression. This may indicate that some process in our body affects both depression and white blood cells.
If we could determine what the overall process is, this could lead to a better understanding of the causes of depression, and it could be a target for treatment.
Correlation vs Causality
Our study showed that there is a correlation between the genetics of mental illness and factors in the blood, but this does not tell us whether blood biomarkers are involved in what causes mental illness.
To distinguish correlation from causation in medicine, the gold standard is to conduct clinical trials in which patients are randomly given treatment or placebo. However, such tests are expensive and difficult to perform.
We did the following: we used DNA variants associated with changes in blood biomarkers as a natural clinical trial. This process exploits the fact that we randomly inherit DNA variants from our parents, just like clinical trial participants randomly receive a treatment or a placebo.
This is a complex method and the results require careful interpretation.
We have found evidence that certain substances measured in the blood may indeed be implicated in the causes of certain mental illnesses. For example, proteins associated with the immune system may be involved in depression, schizophrenia, and anorexia.
More work now needs to be done to determine exactly how these blood counts are involved in these disorders and to see if they can be targeted for treatment.
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