A wide range of mental disorders share common genetic roots, scientists have found, paving the way for simpler and cheaper treatments.
Currently, mental illnesses like bipolar disorder, depression and anxiety are often treated as completely separate conditions, requiring multiple medications that may target different mechanisms and lead to their own side effects.
However, an international team of researchers discovered that many mental health disorders may be genetically connected.
By mapping the entire human genome, which provides a complete blueprint of human DNA, they identified 101 specific regions on human chromosomes where genetic variations contribute to the risk of suffering from multiple psychiatric conditions at once.
Based on this shared genetic architecture, scientists divided the disorders into five distinct groups, including internalizing disorders, which encompass depression, anxiety, and PTSD, and neurodevelopmental disorders such as autism and ADHD.
One key region on chromosome 11 was connected to eight different conditions, including schizophrenia and depression.
Currently, many patients end up taking multiple medications because the first, second or third drug did not work or caused intolerable side effects. Doctors add or switch medications in an attempt to find a combination that manages symptoms. People may also be taking multiple medications because of multiple diagnoses.
By identifying the correct biological cluster from the start, the first treatment choice has a much higher chance of being effective, potentially preventing the need to add more pills to compensate for an ineffective core treatment.
Nearly 48 million Americans have experienced depression or are being treated for it and 40 million suffer anxiety. These conditions often overlap (stock)
For the study, disorders were divided into five distinct groups: Substance Use Disorders, such as alcohol and opioid dependence; Internalizing Disorders, including depression, anxiety, and PTSD; Neurodevelopmental Disorders, like autism and ADHD; Compulsive Disorders, encompassing anorexia, OCD, and Tourette’s syndrome; and the SB group that included Schizophrenia and Bipolar Disorder.
The analysis pinpointed hundreds of individual genetic markers. It identified 238 variants linked to at least one of the five major psychiatric risk categories.
It also found 412 distinct variants that help explain clinical differences between disorders.
Internalizing disorders form one of the most genetically interconnected groups identified in the study, published in the journal Nature.
The three conditions showed the highest level of shared genetic risk among all disorders analyzed, meaning that genetic factors that influence susceptibility to one disorder tend to influence the others as well.
This strong overlap helps explain why people diagnosed with one of these conditions frequently meet the criteria for another, either simultaneously or over their lifetime.
Of the five clusters, the schizophrenia and bipolar disorder group showed the most genetic overlap, about 70 percent, suggesting that a large, shared set of genetic risk factors influences a fundamental set of brain functions and development pathways seen in both bipolar and schizophrenia.
This could explain the well-documented clinical overlap, including shared symptoms like psychosis, frequent misdiagnosis and the occurrence of both disorders in families.
The percentage of adults who report having been diagnosed with depression has reached 29 percent, which is almost 10 percentage points higher than in 2015
Substance-use disorders are characterized by physical and emotional dependence on a substance, like drugs or alcohol.
The shared genetic underpinnings of the addiction disorders likely influence common underlying mechanisms of the disorders themselves, including reward processing, impulse control, response to stress, and, potentially, the metabolic pathways involved in processing the drugs.
The neurodevelopmental disorders cluster encompasses disorders rooted in early brain development. This cluster is primarily defined by a strong shared genetic foundation between autism spectrum disorder (ASD) and ADHD.
This strong genetic overlap suggests that a core set of genes influences early brain development, shaping connectivity, synaptic function, and the regulation of attention and social behavior.
This could explain why, according to findings in the journal Research in Autism Spectrum Disorders, autism and ADHD frequently co-occur and why they share symptoms like challenges with executive function and social interaction.
Tourette’s Syndrome showed a weaker genetic link to the neurodevelopmental cluster, suggesting it shares some risk factors with ASD and ADHD, likely in motor control and impulse regulation, but is driven more by its own distinct genetic mechanisms.
The compulsive disorders cluster has a shared genetic component for disorders centered on intrusive thoughts and repetitive behaviors. This group is defined by a strong link between anorexia and obsessive-compulsive disorder (OCD).
Past research has indicated this overlap suggests that inherited biological pathways related to cognitive control, perfectionism, behavioral rigidity and reward processing contribute to both the ritualistic behaviors seen in OCD and the restrictive, compulsive eating patterns central to anorexia.
The graph from the CDC shows the percentages of adults 18 and up who experienced anxiety symptoms over the past two weeks by severity, according to the most recent CDC data
In the future, a simple blood test could reveal a person’s genetic risk for mental health conditions. By analyzing a patient’s genetic profile, doctors could pinpoint their specific risk patterns, like a high genetic tendency for depression, anxiety or PTSD.
Doctors could use this result to choose a medication or therapy that is most likely to work for them right away, instead of guessing.
Developing a patient’s genetic profile can pinpoint the root of severe anxiety, for example.
If a patient’s genetic profile links their anxiety to the Internalizing cluster, it would point a doctor toward one set of preferred treatments.
If, however, their anxiety is genetically tied to the Compulsive cluster, it would indicate a completely different approach.
The most applicable tests available today are pharmacogenetic tests such as GeneSight or Genomind, which are often offered by psychiatrists.
These analyze how one’s genes affect their metabolism of specific psychiatric medications, helping to predict which drugs they may tolerate better or process poorly, thereby reducing side effects and shortening the trial-and-error period.
So far, no test can say whether someone’s depression is biologically of the ‘Internalizing’ type or the ‘SB’ type. That level of biological subtyping is still in the early research phase.
