- Dyslexia has a strong genetic component, with 40% to 70% of the variation in dyslexia risk being hereditary.
- Researchers found that dyslexia risk genes are associated with brain volume reductions, particularly in regions linked to language processing, motor coordination, and visual processing.
- A key finding was that the primary motor cortex is uniquely linked to dyslexia, distinguishing it from other cognitive traits like intelligence and ADHD.
- Changes in white matter pathways, such as the superior longitudinal fasciculus, suggest that dyslexia is not due to a single brain anomaly but rather a disruption in multiple neural networks.
- While genetic screening for dyslexia is not yet viable, combining genetic research with cognitive assessments may lead to more personalized educational strategies in the future.
Dyslexia is a common neurodevelopmental condition that affects reading and spelling abilities. Although it is unrelated to intelligence, it stems from variations in how the brain processes language. A groundbreaking study published in Science Advances analyzed genetic data from 23andMe and MRI scans of over 30,000 individuals in the UK Biobank, uncovering links between dyslexia risk genes and structural brain differences. These findings provide critical insights into how genetic predisposition might shape brain function, affecting regions involved in language, motor coordination, and visual processing.
Dyslexia: A Genetic and Neurological Overview
Dyslexia impacts an individual’s ability to decode written language, making reading and spelling particularly challenging. One of the hallmarks of dyslexia is difficulty with phonological processing, or the ability to recognize and manipulate the sounds in words. Other common challenges include verbal memory issues, slower processing speed, and difficulties with written word recognition.
The Role of Genetics in Dyslexia
Family studies and twin studies consistently show that dyslexia is highly heritable, with an estimated 40% to 70% of the variation in dyslexia risk being inherited (Soheili-Nezhad et al., 2024). This means that individuals with a family history of dyslexia are significantly more likely to develop the condition.
Researchers have identified multiple dyslexia risk genes, many of which are involved in brain development, neural migration, and synaptic plasticity—key processes that shape how brain circuits form and function. However, until recently, science had not clearly established how these genetic variations impact the brain structurally and functionally.
Major Findings: How Dyslexia Risk Genes Affect the Brain
By combining genetic data and neuroimaging, researchers have pinpointed specific brain differences associated with dyslexia risk genes.
Key Brain Differences Found in People with Dyslexia Risk Genes
- Gray Matter Reduction: A notable decrease in overall brain volume, particularly in gray matter, the part of the brain responsible for processing information.
- Disruptions in Language-Related Brain Regions: Alterations in areas crucial for phonological processing and verbal comprehension.
- Influence on Motor Coordination: Unexpected associations between dyslexia risk genes and the primary motor cortex, implicating difficulties in movement and coordination.
- Visual Processing Differences: Differences in white matter tracts involved in visual-spatial recognition, which may explain letter reversals and difficulties recognizing words.
Key Brain Regions Affected by Dyslexia Risk Genes
Language and Phonological Processing
One of the most critical findings involves reduced brain volume in the left temporoparietal junction and the left anterior insula. These regions are essential for processing spoken and written language, playing a key role in phonological processing, reading fluency, and spelling.
Since dyslexia is primarily characterized by weaker phonological awareness, these structural differences provide compelling evidence that dyslexia is rooted in biological variations in brain function rather than environmental factors or poor instruction.
Motor Coordination and Dyslexia: A Surprising Connection
Perhaps one of the most unexpected findings was the involvement of the primary motor cortex in individuals with a high genetic risk for dyslexia (Soheili-Nezhad et al., 2024). This highlights a potential link between dyslexia and motor coordination difficulties, which have been reported by individuals with dyslexia but have not always been widely acknowledged as part of the condition.
Children and adults with dyslexia often struggle with fine motor skills, handwriting, and rapid sequential movements, supporting the idea that brain differences in motor processing may contribute to dyslexia.
Visual Processing Impairments
The ability to process visual information efficiently is essential for reading. The study identified structural differences in the forceps major, a white matter structure responsible for connecting the occipital lobes, which are crucial for visual recognition and letter processing.
Some individuals with dyslexia experience visual crowding, letter reversals, or difficulty recognizing words due to these structural differences in white matter. These findings deepen the understanding of how brain function is altered in dyslexia at multiple levels—not just in language processing but also in visual perception and letter recognition.
Dyslexia’s Neural Signature: White Matter Changes
In addition to gray matter differences, the research highlights changes in white matter—the brain’s connective tissue that links different functional regions.
Key white matter changes related to dyslexia include
- Reduced Density in the Superior Longitudinal Fasciculus
- This structure connects language-processing regions in the brain and is weaker in individuals with dyslexia. The reduced connectivity suggests a neural disconnect between speech and language processing areas, leading to challenges in processing written text.
- Changes in Cerebellum-Cortex Pathways
- The cerebellum plays a role in automating tasks, including reading. Previous studies have hinted at cerebellar involvement in dyslexia, and this study further confirms structural changes in cerebellum-related pathways.
These findings support the idea that dyslexia involves disruptions in multiple neural circuits, rather than being confined to a single brain region.
Dyslexia and Other Cognitive Traits: Overlapping Brain Regions
An especially intriguing aspect of the study was the comparison of brain regions linked to dyslexia, intelligence, ADHD, and educational attainment. There was a significant overlap in regions associated with these traits.
However, the primary motor cortex stood out as being uniquely linked to dyslexia—suggesting that dyslexia may involve motor coordination challenges that do not appear in other reading-related cognitive variations.
This distinction reinforces the idea that dyslexia is not just about struggling with language—it may involve broader neural adaptations affecting multiple cognitive functions.
Limitations of the Study and Future Research Directions
Although the study provides compelling insights, some limitations should be noted
- Bias in Sample Selection: The research relied on UK Biobank data, which may not perfectly represent the broader population.
- Self-Reported Dyslexia Diagnoses: The 23andMe dataset depended on self-reported diagnoses, which could introduce inaccuracies.
- Cross-Sectional Data: The study captured only a single time point, making it difficult to establish causality—whether these brain differences are a cause or a consequence of dyslexia.
Future research should include longitudinal studies, particularly in children, to understand how brain changes emerge over time in individuals at risk for dyslexia.
The Future: Could Genetics Guide Dyslexia Interventions?
While genetic screening for dyslexia is not yet a reality, researchers speculate that in the future, polygenic scores—which assess an individual’s genetic risk—could help identify children at risk for dyslexia earlier.
Early identification could enable
- Personalized education plans tailored to an individual’s cognitive strengths and weaknesses.
- Targeted interventions focusing on phonics, motor skills development, and visual processing exercises.
- More effective teaching strategies that account for neuroscientific insights.
However, genetic screening alone is not enough. As Professor Clyde Francks from the Max Planck Institute for Psycholinguistics noted, cognitive and behavioral assessments will remain the most effective predictors of dyslexia for now.
Conclusion
This research represents a significant step forward in understanding how dyslexia risk genes shape brain structure and function. By examining brain differences in language, motor coordination, and visual processing, the study reinforces the view that dyslexia is a complex neurodevelopmental condition with widespread effects on brain networks.
With further research, these findings could one day influence educational strategies and early interventions, providing more effective support for individuals with dyslexia.
Citations
- Soheili-Nezhad, S., Schijven, D., Mars, R. B., Fisher, S. E., & Francks, C. (2024). Distinct impact modes of polygenic disposition to dyslexia in the adult brain. Science Advances. https://doi.org/10.1126/sciadv.adq2754
- Francks, C. (2024). Genetic contributions to dyslexia: Brain structure and neural networks. Max Planck Institute for Psycholinguistics.
