Ancestry-enriched and shared polygenic signals associated with high IQ in a Japanese extreme-phenotype cohort

For decades, scientists have known that intelligence is not determined by a single gene, but by thousands of tiny genetic variations working together. Most of our understanding of these variations comes from studying people of European ancestry, creating a massive gap in knowledge about how genetics influence intelligence in other parts of the world. Because genetic patterns differ across populations, a discovery made in one group does not always translate to another. This limitation means that important genetic clues specific to other groups, such as people of East Asian descent, might remain hidden if researchers only look at data from Europe. To fill this gap, a team of researchers turned their attention to a specific group of Japanese individuals with exceptionally high cognitive abilities, aiming to see if they could find unique genetic signals that had been missed by previous studies, while also checking if the general genetic rules for intelligence found in Europe still applied to them.

The researchers began by assembling a very specific group of participants. They recruited 91 Japanese individuals who had scored 140 or higher on a specialized test designed to measure fluid reasoning, a core component of intelligence. This score places them well above the average, which is set at 100. These participants were drawn from a community of high-ability individuals, many of whom were members of Mensa, an organization for people with high intelligence scores. To compare this group, the team used genetic data from 41,528 Japanese people who had taken commercial genetic tests but had not been tested for intelligence. This massive difference in group size—91 people with high scores versus over 41,000 without—allowed the researchers to look for genetic markers that were significantly more common in the high-scoring group. They analyzed nearly 363,000 genetic variants across the entire genome to see which ones stood out.

The study uncovered one specific genetic change that reached the highest level of statistical significance. This change, located in a region of DNA that helps control a gene called PPP2R1A, was found to be much more common in the high-IQ group than in the general control group. In the people with high scores, this genetic variant appeared about five times more often than in the control group. What made this finding particularly interesting was its distribution across different populations. When the researchers looked at global genetic databases, they found that this specific variant is rare in European populations but appears much more frequently in East Asian populations. In fact, it was nearly forty times more common in East Asian genomes than in European ones. This suggests that if scientists had only looked at European data, they would have likely missed this clue entirely because the variant is too rare there to be detected. The gene involved, PPP2R1A, is known to be important for brain development, and mutations in it are linked to various neurodevelopmental conditions, making it a biologically plausible candidate for influencing intelligence.

Beyond this single, unique discovery, the researchers also investigated whether the thousands of tiny genetic effects that influence intelligence in Europe also play a role in Japan. They took the genetic data from the European studies and applied it to their Japanese participants to see if the same patterns held true. They found that the genetic signals did align in a meaningful way. When they looked at the top genetic variants identified in Europe, they found that these same variants tended to point in the same direction in the Japanese high-IQ group. While the effect of any single variant is very small, the combined weight of these shared signals was strong enough to be statistically significant. This indicates that while there are unique genetic factors specific to East Asian populations, there is also a shared biological foundation for intelligence that crosses population boundaries.

To test how well these shared signals could predict high intelligence, the researchers created a composite score based on the European findings and applied it to their Japanese participants. They found that people with higher scores on this composite measure were more likely to be in the high-IQ group. The predictive power of this score was modest but clear, suggesting that the genetic architecture of intelligence is partly universal. However, the researchers were careful to note that this score is not a tool for diagnosing or predicting intelligence in individuals. The study was designed to understand the biology of intelligence at a group level, not to provide a test for individuals. The small size of the high-IQ group and the fact that most participants were men mean that the results need to be confirmed in larger, more diverse studies before they can be considered definitive.

The study concludes that intelligence is shaped by a mix of shared genetic factors and population-specific ones. By focusing on an understudied population, the researchers were able to find a genetic variant that is common in East Asia but rare elsewhere, highlighting the importance of studying diverse groups to get a complete picture of human genetics. At the same time, the confirmation that European genetic findings largely apply to Japanese populations suggests that the fundamental biological mechanisms of intelligence are consistent across different human groups. This work does not solve the mystery of intelligence, but it adds a crucial piece to the puzzle, showing that while the specific genetic clues may vary by ancestry, the overall story of how genes influence the mind is a shared human experience.