Is Dyslexia Genetic? Study Identifies 42 Genes Tied to the Learning Disorder
In the largest genetic study of dyslexia to date, researchers uncovered genetic variations linked to the learning disorder and confirmed the genetic correlation between dyslexia and both ADHD and ambidexterity.
November 9, 2022
New research has identified 42 genes responsible for dyslexia, a language-based learning disorder, and confirmed its genetic link to attention deficit hyperactivity disorder (ADHD) in what is considered the largest genome-wide association study (GWAS) of dyslexia to date. Scientists from the Max Planck Institute for Psycholinguistics, QIMR Berghofer Medical Research Institute in Australia, the University of Edinburgh, and the U.S.-based consumer genetics company 23andMe, Inc. conducted the study and published their findings in the journal Nature Genetics. 1
“Family studies of dyslexia suggest heritability up to 70%, yet few convincing genetic markers have been found… meaning that this study changes our perspective on dyslexia genetics in a big way,” researchers said.
Study participants drawn from the customer base of 23andMe, Inc. included 51,800 adults with dyslexia (21,513 male, 30,287 female) and 1,087,070 (446,054 male, 641,016 female) without dyslexia. Their ages ranged from 18 to 110 years.
DNA was extracted from saliva samples and genotyped on one of five genotyping platforms by the National Genetics Institute (NGI). The study scanned genetic markers across the participants’ DNA sets to find genetic variations associated with dyslexia.
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.
“Previous work suggested some brain structures may be altered in people with dyslexia, but we did not find evidence that genes explain this,” said lead researcher Michelle Luciano, Ph.D., of the University of Edinburgh’s School of Philosophy, Psychology, and Language Sciences in Scotland. “Our results also suggest that dyslexia is very closely genetically related to performance on reading and spelling tests, reinforcing the importance of standardized testing in identifying dyslexia.”
ADHD and Dyslexia
The study also found a “moderate genetic correlation” between ADHD and dyslexia (“24% reporting ADHD in our cases versus 9% in controls”). Researchers said this could potentially reflect “shared endophenotypes like deficits in working memory and attention” but cautioned that this correlation does not mean that all or even most people with dyslexia have ADHD.2
“We already knew from prior studies that dyslexia and ADHD often co-occur; our findings show that this may be (in part) because some of the same genes are involved in both conditions,” Luciano said. (According to a 2013 study published in the Journal of Learning Disabilities, 25% to 40% of individuals with ADHD also have dyslexia.) 3
Cheryl Chase, Ph.D., discussed the overlap between ADHD and dyslexia in the ADDitude ADHD Experts webinar titled “When Dyslexia and ADHD Overlap: Symptoms, Misconceptions, and Interventions.” “ADHD and dyslexia both may bring difficulties with focusing and paying attention,” Chase said. “For an individual with ADHD, these challenges are persistent across settings and circumstances. For someone with dyslexia, these secondary signs tend to appear when reading and language demands spike.”
Researchers noted in the study that common genetic differences have very similar effects in boys and girls. They also found a genetic link between dyslexia and ambidexterity — though not between left-handedness and dyslexia — and between dyslexia and pain-related traits, suggesting that individuals with dyslexia may have a lower threshold for pain perception.
“The genetic correlations observed in this study point to other outcomes and aspects of behavior that one might wish to be mindful of when supporting a person with dyslexia,” Luciano said.
These findings, she said, may be of use “to other scientists who are seeking to understand why dyslexia co-occurs with ADHD, for example, or why there is a correlation with heightened pain sensitivity” and that more research is needed “to understand the functions and the potential mechanisms through which the 42 genetic variants influence cognitive processes.”
“Another major limitation of our work is that, for practical reasons, the GWAS was based on individuals with white European genetic ancestry, so more work is needed in populations with other ancestries to understand if the same genes and DNA variations contribute,” Luciano said. “We found that these kinds of genetic variants explain perhaps a third of the heritability of dyslexia. Hence, most of the genetic variation underlying dyslexia is still undiscovered.”
That said, several of the associated genetic variants were significant in a sample of Chinese-speaking study participants, suggesting that the general thinking processes in learning to read are not dependent on a particular language.
Researchers are optimistic that the findings from the study could potentially “expand diagnostic capabilities, facilitating earlier identification of individuals prone to dyslexia and co-occurring disorders for specific support.”
What Is Dyslexia?
Dyslexia is a neurodevelopmental disorder characterized by severe reading difficulties that exists in 5% to 17.5% of the population, depending on diagnostic criteria. 4, 5
“Contrary to popular belief, dyslexia is not reading letters or words backward,” said Roberto Olivardia, Ph.D. “It manifests itself in different ways in different people. Dyslexics may have difficulty with phonemic awareness, which is the recognition and breaking down of the sounds of letters. A difficulty in segmenting words is also common to the disorder…. Rhyming and fast, effortless recognition of sight words (such as ‘the’) are also problems. All these difficulties affect the rate, accuracy, fluency, and comprehension of material that is read.”
“Strictly speaking, dyslexia is not hazardous to the health. But when dyslexia symptoms are left unidentified and interventions missed, it can cause psychological, academic, and professional harm,” Olivardia said. “Yet, studies show that, when symptoms are identified early, children exude a strong sense of control and confidence; their scores on self-esteem rating scales mirror those of their non-dyslexic counterparts.”
View Article Sources
1Doust, 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
2 Willcutt, E. G., Pennington, B. F., Olson, R. K., Chhabildas, N. & Hulslander, J. (2005). Neuropsychological analyses of comorbidity between reading disability and attention deficit hyperactivity disorder: in search of the common deficit. Dev. Neuropsychol. 27, 35–78.
3 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
4 Shaywitz, S. E., Shaywitz, B. A., Fletcher, J. M. & Escobar, M. D. (1990) Prevalence of reading disability in boys and girls: results of the Connecticut Longitudinal Study. JAMA. 264, 998–1002.
5 Katusic, S. K., Colligan, R. C., Barbaresi, W. J., Schaid, D. J. & Jacobsen, S. J. (2001) Incidence of reading disability in a population-based birth cohort, 1976–1982, Rochester, Minn. Mayo Clin. Proc. 76, 1081–1092.