Study Identifies Significant Genetic Overlap Between ADHD, Dyslexia
ADHD and dyslexia share 174 genes, including 121 previously unidentified ones, and 49 genetic regions, the majority of which are newly discovered.
September 30, 2024
ADHD and dyslexia share 174 genes and 49 genetic regions, according to a new study published in Molecular Psychiatry. The findings suggest that ADHD more closely resembles a learning difference than a psychiatric disorder.1
Led by a team of researchers from the University of Edinburgh, UK, the study aimed to find common genes underlying dyslexia and 10 neurodevelopmental and psychiatric conditions, including ADHD, autism, anorexia nervosa, anxiety, bipolar disorder, major depressive disorder, obsessive-compulsive disorder, schizophrenia, and Tourette syndrome.
The researchers identified five genetically linked clusters, known as latent genomic factors, that revealed ADHD to be more significantly associated with attention and learning issues than it is with neurodevelopmental conditions, such as autism and Tourette syndrome.
Further analysis showed that dyslexia and ADHD share 49 genetic regions, 40 of which were newly discovered, and 174 genes, including 121 previously unidentified ones.
Dyslexia and ADHD
Dyslexia is a language-based learning disorder with neurodevelopmental origins. It is characterized by reduced accuracy and speed in reading and spelling. Dyslexia and ADHD are highly comorbid. Roughly one-quarter to 40% of individuals with ADHD also have dyslexia.2
“Considerable overlap exists between dyslexia and ADHD,” said Cheryl Chase, Ph.D., in the ADDitude webinar “When Dyslexia and ADHD Overlap: Symptoms, Misconceptions, and Interventions.” “ADHD and dyslexia are both linked to problems in school and with learning, but for different reasons. Ultimately, these overlapping traits complicate evaluations for ADHD and dyslexia, especially when both conditions are present. Nevertheless, a thorough evaluation that carefully considers each symptom cluster is critical to receive appropriate support.”
Strong heritability exists for both dyslexia and ADHD. Twin studies of dyslexia estimate its heritability at 60% to 70%.3, 4 Heritability for ADHD ranges from 77% to 88%.5
Previous genome-wide association studies have struggled to identify genes common to people with dyslexia and ADHD, largely because such research would require a substantial sample size. The UK study examined large public anonymized datasets of genetic data from the Psychiatric Genomics Consortium genome-wide association study and dyslexia genetic statistics from an analysis of roughly one million people in collaboration with 23andMe, a U.S.-based consumer genetics company.
The researchers also leveraged the findings of a 2022 study that included data from more than 1.1 million individuals (51,800 dyslexia cases). The 2022 study identified 42 genes responsible for dyslexia and confirmed its genetic link to ADHD. Of the 42 genetic variants identified, 15 were in genes linked to cognitive ability/educational attainment and 27 were new, suggesting that individuals with more genetic variants were more likely to have dyslexia.6
The UK study used a combined sample of 453,408 cases and 2,374,026 controls.
“This is the first time that genetic links to dyslexia have been studied in the context of psychiatric traits,” says Austėja Čiulkinytė, a translational neuroscience Ph.D. student at the University of Edinburgh, who led the study. “In the future, other learning difficulties such as dyscalculia or dysgraphia should be included to allow for a more nuanced understanding of their relationships.”
View Article Sources
1 Čiulkinytė, A. et al. (2024). Genetic Neurodevelopmental Clustering and Dyslexia. Molecular Psychiatry. https://doi.org/10.1038/s41380-024-02649-8
2 DuPaul, G.J., Gormley, M.J., & Laracy, S.D. (2013). Comorbidity of LD and ADHD: Implications of DSM-5 for assessment and treatment. Journal of Learning Disabilities; 46(1), 43–51. https://doi.org/10.1177/0022219412464351
3 Hawke, J.L., Wadsworth, S.J., DeFries, J.C. (2006). Genetic Influences on Reading Difficulties in Boys and Girls: The Colorado Twin Study. Dyslexia; 12:21–29. https://doi.org/10.1002/dys.301
4 Hensler, B.S., Schatschneider, C., Taylor, J., Wagner, R.K. (2010). Behavioral Genetic Approach to the Study of Dyslexia. J Dev Behav Pediatrics; 31:525–32.https://doi.org/10.1097/DBP.0b013e3181ee4b70
5 Faraone, S.V., & Larsson, H. (2019). Genetics of Attention Deficit Hyperactivity Disorder. Molecular Psychiatry; 24(4), 562–575. https://doi.org//10.1038/s41380-018-0070-0
6 Doust, C., Fontanillas, P., Eising, E. et al. (2022). Discovery of 42 Genome-Wide Significant Loci Associated with Dyslexia.Nat Genet.https://doi.org/10.1038/s41588-022-01192-y
