Genetic evidence confirms ADHD symptoms cause poorer academic performance in kids

Children who display more symptoms of attention-deficit/hyperactivity disorder (ADHD) tend to earn lower grades in school, and new research provides evidence that these symptoms directly cause poorer academic performance. By applying advanced genetic models to data from twins and siblings, scientists found that ADHD symptoms negatively affect grades, while grades do not appear to influence the severity of ADHD symptoms. The study was published in Behavior Genetics.

Attention-deficit/hyperactivity disorder, or ADHD, is a common neurodevelopmental condition characterized by persistent patterns of inattention, hyperactivity, and impulsivity. These symptoms are highly heritable, meaning that the condition is strongly influenced by genetics. For years, scientists have observed that children with more ADHD symptoms tend to struggle academically. However, determining whether the symptoms directly cause poor school performance or if other shared factors are to blame has been a difficult task for researchers.

In medical science, the ideal setup for establishing cause and effect is a randomized controlled trial. But assigning children to experience mental health symptoms is ethically and practically impossible. To get around this, researchers often use a technique called Mendelian randomization. This method uses genetic variations as a stand-in for the exposure of interest, like ADHD. Because genes are assigned randomly at birth, they are less likely to be influenced by environmental factors that might confuse the results.

But Mendelian randomization has its own weaknesses. One major issue is horizontal pleiotropy, a scenario where a genetic variant influences the outcome through entirely different biological pathways, rather than just through the condition being studied. If a gene associated with ADHD also independently affects how a child learns, the results could be skewed. To address this problem, the authors of the current study combined genetic tools with data from twins and siblings. This approach allowed them to test the direction of the effect between ADHD symptoms and school grades while filtering out the noise of shared family environments and complex genetic overlap.

The research, led by Luis F. S. Castro-de-Araujo of Virginia Commonwealth University, utilized data from the Adolescent Brain Cognitive Development Study. This large-scale, long-term project tracks the development of thousands of children across the United States. For this analysis, the team focused on 1,523 twin and sibling pairs, as well as some individual children, during the third year of the study’s follow-up.

To measure ADHD symptoms, the researchers used a standard questionnaire called the Child Behavior Checklist, which was completed by the children’s caregivers. The caregivers also reported the children’s school grades from the previous year. Additionally, the researchers calculated polygenic risk scores for the participants. A polygenic risk score is a single number that estimates a person’s genetic likelihood of developing a specific trait based on millions of small genetic variants. In this case, the team calculated scores for both ADHD liability and educational attainment, focusing on a subsample of 1,071 children of European ancestry because the reference genetic data available was limited to that population.

The researchers fed these measures into a series of complex statistical models designed for twin data. The most advanced of these models allowed the team to look at causation in both directions at once. They could see if ADHD symptoms reduced grades and if low grades worsened ADHD symptoms, all while accounting for shared genetics, shared home environments, and horizontal pleiotropy.

The analysis provided evidence that ADHD symptoms have a direct, negative effect on a child’s school grades. When looking at the reverse direction, the researchers found that school grades did not have a statistically significant effect on ADHD symptoms. The team also tested whether these patterns differed between boys and girls. Despite ADHD being diagnosed more frequently in boys, the mathematical models showed that the negative effect of the symptoms on academic performance was consistent across both sexes.

The findings are in line with research covered by PsyPost in 2023, which found that higher ADHD symptoms were associated with lower educational attainment across adolescence. In that earlier Dutch study, academic achievement was evaluated through secondary school educational track placement rather than caregiver-reported grades, but both studies point to similar academic hurdles for youth dealing with ADHD symptoms.

As with all research, there are some caveats to consider. First, the data for the third year of the study was collected during the COVID-19 pandemic. The disruptions to daily life and schooling during this period might have affected the grades reported by caregivers, potentially introducing extra noise into the data.

Another thing to keep in mind is the measurement of the symptoms themselves. The questionnaire completed by caregivers is a highly reliable research tool, but it is not the same as a formal clinical diagnosis of ADHD made by a medical professional.

The study’s reliance on genetic data from people of European ancestry also limits how broadly the findings can be applied. Because comprehensive genetic reference data for other populations is currently lacking, the researchers could only run their most advanced causal models on a specific subset of the participants. Future research will need to include diverse genetic data to ensure these findings apply to all populations. The authors also suggest that future studies track individual children over longer periods to see how symptom persistence influences academic performance as they grow older.

The study, “ADHD and Student Grades in Children from the ABCD Study®: A Twin and Siblings Study,” was authored by Luis F. S. Castro-de-Araujo, Daniel Zhou, Mei-Hsin Su, Sydney Kramer, Robert Loughnan, and Michael C. Neale.