A new study published in Molecular Psychiatry has uncovered genetic connections between dyslexia and attention deficit hyperactivity disorder (ADHD), offering the strongest evidence yet of shared genetic influences between the two conditions. Scientists analyzed vast datasets encompassing millions of participants, providing a clearer picture of how genetic factors may contribute to the frequent co-occurrence of these neurodevelopmental traits. The findings not only confirm the genetic overlap between dyslexia and ADHD but also identify novel genetic variants associated with both conditions.
Dyslexia is a learning difficulty characterized by persistent challenges with reading, spelling, and writing despite normal intelligence and adequate education. It affects how the brain processes language, often leading to difficulties in recognizing written words, decoding sounds, and spelling accurately.
ADHD is a neurodevelopmental condition marked by persistent patterns of inattention, hyperactivity, and impulsivity that interfere with daily functioning. Individuals with ADHD may struggle with maintaining focus, organizing tasks, or controlling impulses, which can impact academic, occupational, and social activities.
Dyslexia and ADHD often co-occur, with approximately 25-40% of individuals diagnosed with one condition also meeting the criteria for the other. While previous research has pointed to genetic influences in both disorders, the exact nature of their genetic relationship remained unclear. Most genetic studies on neurodevelopmental and psychiatric disorders have focused on individual conditions, neglecting the broader connections among traits.
“At the outset of this study, we had solid evidence suggesting a genetic link between dyslexia and ADHD. However, it was far less clear whether dyslexia might also share genetic links with other childhood traits, particularly autism,” explained study author Austėja Čiulkinytė, a PhD student in the Translational Neuroscience PhD program at the University of Edinburgh.
“Previous genetic studies have focused on comparisons of two traits, such as studying dyslexia and ADHD or dyslexia and autism. We wanted to take a broader approach by using a technique that examines the underlying genetics of multiple traits together. This allowed us to investigate whether there might be a shared set of genes across all neurodevelopmental traits, or whether they form genetically distinct categories.”
To investigate the genetic overlap between dyslexia and ADHD, the researchers utilized publicly available genetic data from large-scale studies. The datasets included information on over 453,000 individuals diagnosed with one of ten neurodevelopmental or psychiatric conditions, such as autism, anxiety, and schizophrenia. Dyslexia-related genetic data came from an analysis of over one million participants, conducted in collaboration with the genomics company 23andMe.
The research team used advanced statistical methods to build a genetic model that clustered these conditions based on shared genetic influences. They employed genomic structural equation modeling, a technique that identifies patterns of genetic correlations among multiple traits. The analysis focused on identifying latent genetic factors—underlying clusters of traits with shared genetic liability—and pinpointing specific genetic variants that influence both dyslexia and ADHD.
“By studying many related behaviors together, we are able to boost the statistical power for gene discovery,” said senior author Michelle Luciano, a professor of psychology and language sciences at the University of Edinburgh.
The researchers identified a new genetic factor that clusters dyslexia and ADHD together, which they referred to as the “attention and learning difficulties” factor. This latent factor represents the genetic commonalities that underlie traits related to challenges in reading, attention, and cognitive performance. This factor was separate from other clusters of traits, such as neurodevelopmental disorders, internalizing disorders (e.g., anxiety and depression), and psychotic disorders (e.g., schizophrenia and bipolar disorder).
Dyslexia and ADHD displayed a moderate genetic correlation of 0.40, indicating a substantial overlap in genetic influences. This finding is consistent with previous twin and family studies, which have shown that these two conditions often co-occur and may share common biological pathways.
Interestingly, the study found no significant genetic correlation between dyslexia and autism, despite some overlapping traits, such as difficulties with sensory processing. This suggests that dyslexia and ADHD are more closely related genetically than dyslexia and autism.
“Our original hypothesis was the opposite of what we found,” Čiulkinytė told PsyPost. “Initially, we thought that dyslexia, ADHD, and autism would all fall under the same genetically correlated cluster. However, the data showed that this was not the case.”
“In this study, we show that dyslexia and ADHD in fact share a distinct set of genetic influences, which are different from those of other neurodevelopmental traits. We propose that in the context of genetics, ADHD might be better understood as an attention and learning difficulty (like dyslexia) rather than a purely neurodevelopmental trait (like autism).”
One of the most groundbreaking aspects of the study was the discovery of 49 genomic regions associated with both dyslexia and ADHD, 43 of which had not been previously identified. These regions were mapped to 174 protein-coding genes, many of which play crucial roles in brain development, synaptic signaling, and cognitive processes.
Among these genes, SORCS3, TRAIP, AMT, and TCTA emerged as particularly noteworthy candidates. For example:
- SORCS3 is involved in neural signaling and synaptic plasticity, processes critical for learning and memory. It has been linked to reduced spatial learning abilities, which are often affected in both dyslexia and ADHD.
- TRAIP is essential for maintaining genome integrity and has been associated with cognitive function and intelligence in previous studies.
- AMT plays a role in neuronal development and has been strongly associated with educational attainment, a trait negatively impacted by both dyslexia and ADHD.
- TCTA has been implicated in cognitive performance and problem-solving abilities, further highlighting its relevance to attention and learning processes.
The attention and learning difficulties factor identified in the study showed strong correlations with traits related to academic and cognitive performance. For example, individuals with genetic predispositions to dyslexia and ADHD were more likely to struggle with linguistic and mathematical tasks, such as reading comprehension and problem-solving. The factor also negatively correlated with measures of educational attainment, such as the likelihood of obtaining higher qualifications or completing formal education.
The study sheds light on the complex genetic connections between dyslexia and ADHD, offering a new framework for understanding their frequent co-occurrence. However, there are some limitations. The genetic datasets included primarily individuals of European ancestry, which may limit the generalizability of the findings to other populations. Future studies should incorporate more diverse genetic data to ensure broader applicability.
The study also did not include conditions such as dyscalculia or developmental language disorders, which often co-occur with dyslexia and ADHD. Including these traits in future research could provide a more comprehensive understanding of the genetic architecture of learning difficulties.
“In the future, it would be great to extend this analysis by including datasets on genetic influences of other learning difficulties, particularly dyscalculia and dyspraxia,” Čiulkinytė said. “This will help us to better define the set of genes affecting attention and learning difficulties in the broad sense.”
“I think it is important to highlight that our study focuses on population genetics of complex traits: we are studying millions of small genetic changes, each with a tiny effect, across thousands of individuals,” she added. “This type of study allows us to better understand the overall pattern of how dyslexia and ADHD manifest, uncover potential genetic causes, and suggest that they both might benefit from similar management approaches. However, it does not mean that every individual with ADHD is also dyslexic or vice versa.”
The study, “Genetic neurodevelopmental clustering and dyslexia,” was authored by Austeja Ciulkinyte, Hayley S. Mountford, Pierre Fontanillas, 23andMe Research Team, Timothy C. Bates, Nicholas G. Martin, Simon E. Fisher, and Michelle Luciano.
