Shared genes explain why ADHD, dyslexia, and dyscalculia often occur together, study finds

A recent study involving a large group of children has shed light on why attention-deficit/hyperactivity disorder (ADHD), dyslexia, and dyscalculia frequently appear together. Researchers discovered that the likelihood of developing ADHD overlaps genetically with the likelihood of developing dyslexia and dyscalculia. This shared genetic basis helps explain why children with ADHD are more prone to experience difficulties in reading, spelling, and mathematics.

The research was published in Psychological Science.

ADHD is a condition that affects a person’s ability to pay attention, control impulsive behaviors, and manage hyperactivity. Children with ADHD may find it hard to concentrate on tasks, sit still, or wait their turn. Dyslexia is a learning difficulty primarily affecting reading and spelling skills. Individuals with dyslexia often struggle with recognizing and manipulating sounds in words, which makes reading fluently and spelling accurately challenging. Dyscalculia is a learning difficulty that affects the ability to understand and work with numbers. Children with dyscalculia may have trouble with basic arithmetic, understanding mathematical concepts, and solving math problems.

Scientists have long observed that these three conditions—ADHD, dyslexia, and dyscalculia—tend to occur together more often than would be expected by chance. For instance, a child diagnosed with ADHD is more likely to also be diagnosed with dyslexia or dyscalculia compared to a child without ADHD.

To understand the reasons behind this co-occurrence, researchers from the University of Amsterdam and the Vrije Universiteit Amsterdam in the Netherlands embarked on a detailed investigation. They wanted to move beyond simply noting that these conditions often appear together and explore the underlying causes. Specifically, they wanted to determine if this co-occurrence was due to one condition directly causing another, or if there was a different explanation, such as shared risk factors.

“ADHD, dyslexia, and dyscalculia frequently co-occur, but why? Many assume that one condition causes the other. For example, children with learning difficulties may struggle to follow class instructions, which could make it harder for them to pay attention—potentially leading to ADHD symptoms,” explained study author Elsje van Bergen, an associate professor at Vrije Universiteit Amsterdam and a visiting professor at the University of Oslo.

“Conversely, ADHD-related behaviors, such as difficulties with focus and impulsivity, might interfere with learning to read and do maths. However, this assumed causality had not been thoroughly tested. Understanding the underlying causes of these learning difficulties is crucial for designing effective support strategies.”

To conduct their study, the research team utilized data from the Netherlands Twin Register, a comprehensive database that includes information on twins and their families from across the Netherlands. They examined information from 19,125 twins, originating from 10,365 families. This large sample size provided a robust foundation for their findings. The researchers collected data at two different time points when the twins were around 7 years old and again when they were around 10 years old.

To assess ADHD symptoms, the children’s teachers completed questionnaires. These questionnaires asked about behaviors associated with ADHD, such as difficulty paying attention and hyperactivity, in the school setting. It is important to note that these questions focused on ADHD symptoms and did not include items related to learning or academic performance, ensuring a clear distinction between ADHD and learning difficulties.

To measure academic achievement, the researchers used scores from the national Pupil Monitoring System, a standardized testing system used in Dutch schools. This system provided objective measures of the children’s abilities in reading, spelling, and mathematics. Reading ability was assessed by measuring how fluently children could read words from a list. Spelling ability was measured through dictation tests where children had to spell words they heard. Math ability was evaluated using tests covering different areas of mathematics, including numbers, operations, ratios, fractions, measurement, and geometry.

The study revealed that a significant proportion of children experienced more than one of these difficulties. Specifically, the researchers found that 37% of children who met the criteria for ADHD also showed signs of dyslexia or dyscalculia. Looking at the individual conditions, they found that children with ADHD were approximately 2.7 times more likely to have dyslexia and 2.1 times more likely to have dyscalculia compared to children without ADHD. Similarly, children with dyslexia or dyscalculia were also more likely to have ADHD.

However, the most striking finding was related to the underlying causes of this co-occurrence. Through sophisticated statistical analyses, including examining data from twins, the researchers were able to explore the role of genetics. Twin studies are valuable for this type of research because identical twins share nearly all of their genes, while non-identical twins share only about half, similar to regular siblings. By comparing similarities and differences between identical and non-identical twins, researchers can estimate the influence of genes and environment on various traits.

The analyses revealed that the genetic factors that increase the risk for ADHD also overlap with the genetic factors that increase the risk for dyslexia and dyscalculia. In other words, there is a shared genetic predisposition. This means that individuals can inherit genetic variations that make them more susceptible to developing not just one, but potentially all three of these conditions.

The study’s findings strongly suggest that the reason why ADHD, dyslexia, and dyscalculia often occur together is not primarily because one condition directly causes another. Instead, it is because they share common genetic roots. The learning problems seen in children with ADHD are not simply a direct consequence of their attention difficulties, but rather a reflection of this shared genetic vulnerability that affects both attention and learning abilities.

“Our findings suggest that one condition does not directly cause the other one,” van Bergen told PsyPost. “Instead, these conditions often co-occur because they share genetic risk factors. This means that if a child has a genetic predisposition for ADHD, they are also at increased risk for dyslexia and dyscalculia. As a result, treating ADHD alone won’t necessarily improve academic skills, and vice versa.”

“About 75% of differences among children in learning to read, spell, and do math are influenced by genetics. Similarly, differences among children in ADHD symptoms are about 75% due to genetic differences among them. This is not surprising to me, as it confirms earlier findings, but it may be surprising to readers new to behavioral genetics research.

“It is important to stress that this heritability figure refers to differences among children in, for instance, how easily they pick up learning to read,” van Bergen continued. “However, children learn these skills because of high-quality education, so that remains crucial. Teachers will recognize that even with high-quality instruction, pupils vary in the effort needed to learn these skills.”

While this study focused on genetic factors, the findings shouldn’t be misinterpreted as suggesting that environmental factors play no role in the co-occurrence of ADHD, dyslexia, and dyscalculia. Understanding how genes and environment interact could provide a more complete picture.

“While genetics plays a large role, it does not mean that learning difficulties are fixed—early interventions and good teaching can still make a big difference,” van Bergen noted. “In another study, we found that children with a family history of dyslexia also benefit from reading intervention.”

Looking ahead, the researchers aim to further investigate the factors that shape educational outcomes in children. “I aim to better understand how genetic and environmental factors interact to shape children’s educational outcomes,” van Bergen explained. “By including genetics, we can get a clearer picture of what in the environment matters most. This knowledge can then inform research on tailored approaches to support children’s cognitive development.”

“I’d like to emphasize that recognizing the genetic basis of learning difficulties is not about labelling children, but about understanding their needs. Schools and clinicians should be aware that while ADHD, dyslexia, and dyscalculia can co-occur, each requires targeted support. At the same time, most children (77%) with one of these conditions do not have another. This challenges the common assumption that developmental conditions always come in clusters.”

The study, “Co-Occurrence and Causality Among ADHD, Dyslexia, and Dyscalculia,” was authored by Elsje van Bergen, Eveline L. de Zeeuw, Sara A. Hart, Dorret I. Boomsma, Eco J. C. de Geus, and Kees-Jan Kan.