Autism, ADHD and Schizophrenia May Share Genetic Roots

New genetics research indicates that these conditions may be more closely related than previously thought.

New work by US researchers has identified a possible shared biological basis across several familiar psychiatric diagnoses. The findings could alter how clinicians interpret these conditions, assess risk and, in time, treat them.

One genetic network across eight psychiatric diagnoses

Published in Cell in early 2025, the study explored the genetics of eight psychiatric conditions that commonly occur within the same families:

• Autism
• Attention deficit hyperactivity disorder (ADHD)
• Schizophrenia
• Bipolar disorder
• Major depressive disorder
• Tourette syndrome
• Obsessive-compulsive disorder (OCD)
• Anorexia nervosa

The researchers focused on genes previously associated with these conditions, investigating how alternative forms of those genes function as the brain develops.

They found 683 distinct genetic variants that affect gene regulation in brain cells, influencing which genes are activated or silenced, as well as the timing of that activity. Rather than belonging to only one diagnosis, many of these variants were common to several of the eight conditions.

The study suggests that autism, ADHD, schizophrenia and other major psychiatric diagnoses may partly arise from the same sets of genetic switches going awry at key moments in brain development.

How shared genes can produce different conditions

An international research group had previously identified 109 genes, in 2019, that appeared in differing combinations among these eight disorders. That earlier research suggested genetic overlap; the latest study examines more closely what the shared genes do in developing brain cells.

The researchers examined almost 18,000 versions of genes that were either shared between conditions or specific to individual disorders. They introduced these variants into human precursor cells - immature cells that eventually develop into neurons - and assessed how each version changed gene activity.

This laboratory method enabled the team to observe in detail how particular DNA changes can affect both the strength and timing of gene expression. The variants with the greatest effects were then assessed in neurons from developing mice to establish whether the same patterns occurred in a living brain.

The shared variants were associated with a large number of protein–protein interactions. Put simply, the proteins produced by these variants have highly active roles within the brain's molecular network.

Changes in these heavily connected proteins can send ripples through entire cellular systems, potentially nudging development toward several different psychiatric outcomes, not just one.

Pleiotropy: one gene, multiple effects

Geneticists describe this pattern as pleiotropy: a single genetic variant that affects more than one trait or condition.

In this research, pleiotropic variants showed greater connectivity, activity in a wider range of brain cell types, and involvement in regulatory systems functioning across several phases of brain development. Their influence was not confined to one narrow stage of development.

This prolonged activity may help explain why the same genetic change could be linked with autism in one individual, ADHD in another, or both conditions in the same person. The outcome depends on timing, the broader genetic background and environmental influences that affect the brain over time.

Why mental health diagnoses overlap so often

Clinicians have long recognised that psychiatric diagnoses overlap, and many people do not fit cleanly into one diagnostic category.

• Up to 70 percent of people with autism also meet criteria for ADHD.
• Depression is common in people with bipolar disorder or schizophrenia.
• OCD and Tourette syndrome often occur in the same families.

The shared genetic variants identified by the study provide a biological rationale for this pattern. When the same group of genes can shape multiple brain-development pathways, it follows that related conditions may frequently occur together.

The findings may also explain why psychiatric conditions can “run in families” without always taking the same form. A parent with depression may have a child with ADHD or OCD, not because the disorders are identical, but because they share parts of the same genetic architecture.

Rethinking psychiatric diagnostic categories

For many years, pleiotropy has been a challenge for researchers seeking to place mental illnesses into clearly separated diagnostic groups. Genetic overlap has made the lines between conditions such as schizophrenia and bipolar disorder less distinct, prompting difficult questions about whether current categories truly match the underlying biology.

The new study presents a more positive interpretation. Instead of viewing pleiotropy as an obstacle, its authors suggest that understanding it could support therapies aimed at common underlying mechanisms rather than symptoms alone.

If many conditions share the same core genetic vulnerabilities, a single treatment strategy might help patients across several current diagnostic labels.

This has worldwide importance. The World Health Organization estimates that approximately one in eight people globally live with a psychiatric condition. That amounts to nearly a billion people, many of whom do not receive sufficient care.

Finding shared molecular targets could make drug development more efficient and potentially lead to treatments that help several groups at once, rather than demanding an entirely separate therapy for every diagnosis.

Autism, ADHD and schizophrenia in the developing brain: timing, cells and networks

The research identifies three central features of the way these risk genes operate.

Feature	What the researchers found
Timing	Shared variants stay active for longer periods during brain development, rather than acting at only one point.
Cell types	They affect gene activity in several types of brain cell, rather than one specialised cell population.
Networks	The proteins they produce are highly connected and interact with numerous other proteins.

Together, these characteristics mean that the variants may shape broad cascades in brain development, including how neurons grow and how they form connections with one another. Minor changes at an early stage can build up over time.

What the findings do - and do not - mean for patients

The results do not point to one “mental illness gene”, nor do they provide a straightforward test capable of diagnosing conditions at birth. Psychiatry remains much more complex than that.

Most psychiatric disorders result from a combination of many genes, each contributing a small increase in risk, alongside life experiences including stress, trauma, infections, substance use and social factors. Genes can create a background of vulnerability, but they do not determine anyone's future.

The study's main impact may be on the way researchers plan future studies and treatments. Rather than concentrating solely on pathways linked to one diagnosis, drug developers could seek molecular targets positioned at the intersection of several conditions.

For instance, a medicine that restores normal activity in a highly connected protein involved in early neuron development could plausibly be tested in people at risk of autism, ADHD and schizophrenia, instead of in one group only.

Key terms patients may encounter

People reading about this research in clinical letters or news coverage may come across several technical terms. Here is a brief guide:

• Genetic variant: a difference in a DNA sequence that may change the way a gene functions. Most variants are harmless, although some influence disease risk.
• Gene regulation: the process that determines when genes are switched on or off in a cell, and how strongly they are expressed.
• Precursor neuron: an immature cell that has not yet become a fully developed neuron but is progressing towards that state.
• Protein–protein interaction: a physical or functional connection between proteins that forms part of a complex cellular network.
• Pleiotropy: one genetic change affecting several traits or conditions at the same time.

Where the research may go next

Future studies are likely to examine how these shared variants interact with real-world experiences. Two people may carry the same risk variant yet have very different life histories: one may develop severe illness while the other does not. Explaining that difference could help shape prevention approaches as well as medicines.

Another probable next step involves brain organoids - miniature brain-like structures grown from stem cells - which can model how particular psychiatric risk variants affect developing neural circuits in the laboratory. This could offer researchers a controlled setting for testing new medicines or combinations of therapies.

For clinicians and families, the most significant development may be a shift in perspective. Rather than viewing conditions as isolated labels - “this is autism”, “that is bipolar” - psychiatry could gradually move towards a spectrum model based on shared biology. Such a change would not remove the lived reality of any diagnosis, but it could make more flexible, cross-cutting care possible.

People living with a psychiatric condition, and those supporting them, should not expect immediate change from one paper. However, the study makes the scientific picture of how different conditions are connected clearer. That picture will underpin future treatments.