New research suggests that the genetic links between psychiatric conditions and intelligence vary depending on the specific type of thinking skill involved. Rather than viewing intelligence as a single trait, a new genetic analysis indicates that conditions like schizophrenia and bipolar disorder share different genetic roots with problem-solving skills compared to acquired knowledge. The findings were published in Nature Communications.
People diagnosed with certain psychiatric disorders often experience difficulties with memory, attention, and problem-solving. For instance, a 2023 review detailed how conditions like schizophrenia share overlapping genetic and environmental risk factors with cognitive challenges. Similarly, a study covered by PsyPost in 2024 found that higher general intelligence tends to be associated with fewer symptoms of attention-deficit hyperactivity disorder (ADHD) and autism, a connection partly driven by shared genetics.
Past genetic research generally treated cognitive ability as one broad category. However, human cognition is made up of distinct skills. These include processing speed, often measured by how fast someone reacts to a prompt. Another component is fluid reasoning, which involves solving new problems and processing complex information on the spot. A third area is crystallized knowledge, representing the facts and vocabulary a person learns through culture and life experience.
Genetic studies have historically lacked enough data to analyze these specific categories of thinking, especially crystallized knowledge. Scientists wanted to see if breaking down cognition into these specific domains might provide a more detailed picture of how mental health and intelligence are connected at a genetic level. They also wanted to account for non-cognitive skills, such as motivation and persistence, which help people succeed in educational settings.
The research was led by Diego Londoño-Correa, a PhD and recent graduate of the Department of Psychology at The University of Texas at Austin. “There was a paradox in the behavioral and psychiatric genetics literature that I found very interesting,” he said. “People diagnosed with psychiatric disorders such as schizophrenia often show cognitive difficulties, and these negative associations are observed at both the phenotypic and genetic levels. However, genetic liability for schizophrenia and some other disorders has also been positively associated with educational attainment.”
“In our lab, we wondered whether part of this apparent contradiction came from treating cognition as a single trait,” he explained. “We thought that part of the answer to this paradox might lie in the difference between these domains that previous studies had not accounted for.”
The scientists analyzed genetic data from hundreds of thousands of people. Using existing genetic databases, primarily focusing on individuals of European ancestry, they gathered information on cognitive test performance and educational attainment. The total sample size for the crystallized knowledge analysis reached roughly 439,000 individuals.
To measure specific cognitive skills, the team looked at scores from tests involving reaction time, puzzle solving, and vocabulary knowledge. “Many cognitive tests do not ‘purely’ measure a single domain such as crystallized knowledge,” Londoño-Correa explained. “For example, you still need lower-order cognitive processes such as processing speed to perform well on tests of crystallized knowledge, including vocabulary tests.”
To address this, the researchers used a specialized statistical tool to separate the overlapping genetic influences of reaction time, fluid reasoning, and crystallized knowledge. They also isolated a non-cognitive genetic factor tied to how many years of schooling a person completed, removing any genetic effects related to actual test performance.
The analysis identified 78 genetic regions associated with crystallized knowledge. Eight of these regions had never been linked to any cognitive trait in previous genetic research. The researchers also found that genes associated with fluid reasoning tend to be most active in the brain during early childhood development. In contrast, genes associated with crystallized knowledge show increased activity during adolescence and early adulthood, aligning with the idea that this type of knowledge builds up over time through education and experience.
When comparing these cognitive profiles to the genetic risk for five specific psychiatric conditions, the authors found highly varied patterns. Schizophrenia and bipolar disorder showed the most similarity. The genetic risk for both conditions was associated with slower reaction times and lower fluid reasoning, but positively associated with both crystallized knowledge and non-cognitive educational skills.
“The main takeaway is that the genetic relationship between psychiatric disorders and cognitive abilities is not uniformly positive or negative,” Londoño-Correa said. “Reducing all of cognition to a single general factor of intelligence can hide meaningful differences in how psychiatric genetic liability relates to different cognitive abilities.”
Other conditions displayed entirely different genetic associations. The genetic risk for ADHD was associated with slightly faster reaction times, but it was also linked to lower fluid reasoning, lower crystallized knowledge, and lower non-cognitive skills. Autism spectrum disorder was positively associated only with crystallized knowledge. Alzheimer’s disease was associated only with lower fluid reasoning, matching the clinical observation that dementia often heavily impacts executive functioning and on-the-spot problem-solving.
The researchers also compared the cognitive genetic factors to personality traits. They found that openness to experience, a trait linked to curiosity and a desire to learn, was strongly and positively associated with the genetics of crystallized knowledge.
Londoño-Correa found this specificity particularly striking, noting that openness had a strong correlation with crystallized knowledge but much weaker associations with reaction time and fluid reasoning. “Developmental psychologists propose these genetic tendencies as ‘experience-producing drives’ so people who are more curious may seek out books, conversations, education, cultural experiences, or other cognitively rewarding environments,” he said. “Over time those experiences accumulate into crystallized knowledge, the trait that was correlated with higher risk for schizophrenia, bipolar disorder and autism.”
These findings offer new insights, but they are subject to certain limitations. The genetic overlap between a psychiatric disorder and a cognitive trait does not mean that having a specific gene will automatically cause a mental health condition or guarantee high intelligence.
“The most important caveat is that genetic liability is not the same thing as having a psychiatric disorder,” Londoño-Correa explained. “That is very different from saying that people diagnosed with schizophrenia have higher crystallized abilities. We are studying how genetic variation can relate to multiple traits at the same time, not describing the average characteristics of diagnosed individuals.”
He emphasized that the study should not be interpreted as showing that clinical conditions like schizophrenia or autism improve cognition, as these disorders can have very serious cognitive and functional consequences. Furthermore, the study relied entirely on data from people of European descent to avoid statistical errors that can happen when mixing different genetic backgrounds, meaning the results might not apply to other ancestries.
Looking ahead, the research team hopes to use these insights to explore broader evolutionary questions. “My broader interest is in understanding why genetic variation associated with psychiatric disorders persists across human evolutionary history despite the health and reproductive costs these disorders can impose, particularly for conditions that often begin relatively early in life,” Londoño-Correa said.
He pointed to a concept known as antagonistic pleiotropy, where genetic variants that increase vulnerability to a disorder might also confer cognitive or behavioral advantages. “This study does not test natural selection directly, so we need more sophisticated analyses, for example using ancient DNA, to ask whether psychiatric-risk variants that are also associated with higher cognitive performance increased in frequency during human history,” he added.
The study, “Crystallized and fluid cognitive abilities have different genetic associations with neuropsychiatric disorders,” was authored by Diego Londono-Correa, Javier de la Fuente, Gail Davies, Simon R. Cox, Ian J. Deary, K. Paige Harden, and Elliot M. Tucker-Drob.