Mental health conditions and developmental disorders affect hundreds of millions of people around the world.
Disorders such as autism, ADHD, bipolar disorder, schizophrenia, major depression, and chronic insomnia can have profound effects on education, work, relationships, and quality of life. Despite decades of research, scientists still do not fully understand why these conditions develop.
Traditionally, researchers have treated these disorders as separate illnesses because they produce different symptoms. However, growing evidence suggests that there may be important biological links between them. A major international study has now provided new evidence supporting this idea.
Scientists from Fudan University, King’s College London, University Paris-Saclay, and other institutions performed one of the largest investigations so far into the shared biology of psychiatric and neurodevelopmental conditions. Their findings were published in Nature Mental Health.
The researchers focused on genes and the immune system. Although the brain and immune system may seem unrelated, scientists now know that they constantly communicate with each other.
Immune cells release chemical signals that can affect brain development, mood, thinking, and behavior. At the same time, stress and changes in the brain can influence immune responses.
Previous studies have shown that immune system problems are often present in people with psychiatric disorders. People with autoimmune diseases sometimes have higher rates of depression, schizophrenia, or other mental health conditions. This led researchers to wonder whether common biological pathways might connect these seemingly different diseases.
To investigate the question, the scientists examined blood-derived biological information from 1,274 healthy adolescents who participated in the IMAGEN study, a large European research project that follows young people and examines factors that influence brain development and mental health.
The researchers looked for small natural differences in DNA and studied DNA methylation, which works like a dimmer switch that can increase or decrease the activity of genes. They also examined gene expression, which reflects how active specific genes are.
Their analyses uncovered 73 potentially important DNA methylation sites and 62 genes that may contribute to psychiatric and neurodevelopmental disorders. Some of these markers appeared to be linked to only one condition, while others were connected to several different disorders.
Three genes stood out from all the others. These genes were called MAD1L1, MRPL2, and HLA-DRB1. The researchers found evidence that changes affecting these genes may help explain biological processes involved in schizophrenia, insomnia, and possibly other conditions.
The MRPL2 gene appeared to be involved in both insomnia and schizophrenia. Certain chemical changes on DNA reduced the activity of this gene and were associated with increased disease risk. At the same time, increased activity of MAD1L1 and HLA-DRB1 was associated with a greater risk of schizophrenia.
Another important finding was that many of the identified genes were also involved in pathways related to autoimmune diseases. This suggests that some psychiatric disorders and immune disorders may share common genetic and biological mechanisms.
These findings are important because they move researchers beyond simply describing symptoms and toward understanding what may be happening at the molecular level. Discovering biological pathways that are shared by multiple conditions could eventually lead to new therapies that target common mechanisms instead of treating each disorder separately.
However, it is important to remember that this study does not prove that these genes directly cause mental illness. Human behavior and mental health arise from a complex interaction between genes, brain development, family experiences, social environment, and life events. Genes may increase risk, but they do not determine a person’s future.
The study has several strengths. It included a relatively large group of participants and used sophisticated methods to analyze genetics and molecular biology. Nevertheless, the findings still need to be validated in additional populations and in studies that directly examine the brain.
Even with these limitations, the study represents an important step forward. It highlights the possibility that conditions such as autism, ADHD, depression, schizophrenia, and insomnia may not be entirely separate diseases but may share hidden biological roots.
As scientists continue to uncover these connections, new opportunities may emerge for earlier diagnosis, more precise treatments, and a better understanding of how mental health disorders develop.
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Source: Fudan University.
