Dyslexia is caused by differences in how the brain processes written and spoken language, rooted primarily in genetics and brain development rather than intelligence, effort, or vision problems. It affects roughly 5 to 15 percent of the population, and while no single gene or brain region is solely responsible, researchers have identified a consistent set of genetic, neurological, and cognitive factors that converge to make reading unusually difficult.
Genetics Play a Central Role
Dyslexia runs in families. If one of your parents has dyslexia, your chances of having it rise significantly, and studies of identical twins show that when one twin has dyslexia, the other almost always does too. This strong heritability points to genetics as the most important upstream cause.
Researchers have identified several specific genes linked to reading difficulty, including three that have received the most attention: DYX1C1, DCDC2, and KIAA0319. All three influence how neurons develop and migrate during early brain formation. DCDC2 plays a role in neuronal development, while KIAA0319 is involved in neuronal migration, the process by which brain cells move into their correct positions during fetal development. A study published in Biological Psychiatry found that variations in all three genes were significantly associated with differences in white matter volume in the left side of the brain, specifically in a region where pathways connect areas critical for language processing. Less white matter in those pathways means weaker connections between the parts of the brain that need to work together during reading.
These aren’t “dyslexia genes” in the simple sense. They’re normal genetic variants that influence brain development in ways that make reading harder. Many people carry some of these variants without ever being diagnosed. The genetic picture is complex, involving dozens of genes that each contribute a small amount of risk.
The Brain Reads Differently in Dyslexia
Brain imaging studies have consistently shown that people with dyslexia use different neural pathways when they read. The core finding, replicated across many studies, is reduced activation in two left-hemisphere regions that are essential for skilled reading.
The first is a left parietal region involved in connecting the sounds of language to their written forms. When you see the letters C-A-T and mentally hear the word “cat,” this region is doing much of that work. In dyslexia, it’s consistently underactive. The second is a region in the left fusiform gyrus sometimes called the visual word form area. This is the part of the brain that, in skilled readers, recognizes whole words almost instantly, the way you recognize a friend’s face without having to analyze each feature. In dyslexia, this region also shows reduced activity, which helps explain why reading remains slow and effortful even after years of practice.
To compensate, people with dyslexia show increased activation in the left frontal lobe, a region associated with articulation and speech production. Researchers at the Proceedings of the National Academy of Sciences found that this frontal hyperactivation reflects a workaround: the brain recruits extra resources to consciously sound out words that other readers process automatically. It’s as if skilled readers have a highway for word recognition, while people with dyslexia are rerouting through side streets.
These differences aren’t just functional. The physical wiring is different too. Studies of children aged 8 to 11 with dyslexia have found atypical structure in the arcuate fasciculus, a major white matter tract that connects the brain’s language-processing regions. Think of it as the cable that lets the sound-processing and meaning-processing parts of the brain communicate quickly. When that cable is less organized, the whole reading system slows down.
The Phonological Processing Problem
If genetics and brain structure are the biological foundations of dyslexia, the phonological deficit is where those foundations meet the act of reading. Phonological processing is your ability to recognize, manipulate, and recall the individual sounds (phonemes) in spoken language. It is the most well-established cognitive explanation for why dyslexia makes reading so hard.
Reading in an alphabetic language requires you to map written letters onto speech sounds. During early reading, a child has to break a printed word into its letters, assign each letter its corresponding sound, and then blend those sounds together to produce the spoken word. Spelling demands the reverse. A deficit in how the brain represents speech sounds disrupts both processes at their core. This is why the hallmark symptom of dyslexia, beyond slow or inaccurate reading, is difficulty with phoneme awareness: tasks like identifying the first sound in “dog” or saying what “plant” would be without the “l.”
The phonological deficit also shows up in two other ways. First, people with dyslexia are often slower at rapid automatized naming, where you look at a series of familiar images, colors, or letters and name them as quickly as possible. This task relies on the same brain systems that create quick connections between what you see on a page and its spoken form. Second, phonological short-term memory is often weaker, making it harder to hold verbal information (like a phone number or a sequence of instructions) in mind long enough to use it. These aren’t separate problems. They’re different expressions of the same underlying difficulty with how the brain codes and retrieves language sounds.
Prenatal and Environmental Risk Factors
While genetics account for the largest share of dyslexia risk, the environment a child develops in, both before and after birth, can raise or lower that risk. Prenatal exposures including alcohol, drugs, maternal stress, and environmental pollutants have all been linked to reading and learning difficulties. These exposures can interfere with the same neuronal development and migration processes that the dyslexia-associated genes regulate, which means prenatal environment and genetics may sometimes amplify each other.
Premature birth and low birth weight are also associated with higher rates of reading difficulty, likely because the brain’s language circuitry is still forming rapidly during the final weeks of pregnancy. None of these environmental factors are guaranteed to cause dyslexia on their own, but they can push a child who already carries genetic risk over the threshold into noticeable reading impairment. It’s worth noting that environmental disadvantage, lack of adequate reading instruction, and conditions like hearing or vision problems can look like dyslexia but are considered separate causes of reading difficulty under current diagnostic standards.
Dyslexia Often Occurs Alongside Other Conditions
Dyslexia rarely exists in isolation. It frequently co-occurs with ADHD, and this overlap is large enough to be clinically significant. According to 2022 CDC data, about 36.5% of children with ADHD also have a learning disability, with dyslexia being the most common one. The overlap runs in both directions: children diagnosed with dyslexia are also more likely than average to have attention difficulties. Researchers believe shared genetic risk factors influence both conditions, which is why they cluster together in families.
Other conditions that commonly co-occur with dyslexia include dyscalculia (difficulty with math), developmental language disorder, and anxiety or depression, often as a secondary consequence of years of academic frustration rather than a shared biological cause.
The Brain Can Change With the Right Support
One of the most encouraging findings in dyslexia research is that the brain differences associated with the condition are not fixed. A systematic review of brain imaging studies found that targeted reading interventions produce measurable changes in both brain function and brain structure. After intensive phonological training, children with dyslexia show increased activation in the left-hemisphere regions that were previously underactive, a pattern researchers call “normalization” because it brings activity closer to what’s seen in typical readers.
Some children also show increased activation in regions outside the typical reading network, suggesting the brain develops alternative support pathways alongside the more conventional ones. Changes aren’t limited to how the brain fires during reading tasks. Studies have documented intervention-related increases in gray matter volume, cortical thickness, and white matter organization. These structural changes confirm that the brain physically reorganizes in response to effective instruction, not just functionally but in its actual tissue.
This doesn’t mean dyslexia goes away. Most people with dyslexia continue to read more slowly than average throughout their lives, even after successful intervention. But the brain’s capacity to rewire itself means that the severity of the difficulty is not predetermined by genetics or early brain development alone. The timing and quality of support matters enormously.
What Dyslexia Is Not
Dyslexia is not caused by laziness, low intelligence, or “seeing letters backwards.” The letter-reversal myth persists, but reversals are common in all beginning readers and are not a defining feature of dyslexia. The condition is also not caused by poor parenting or insufficient reading at home, though a language-rich environment can help buffer genetic risk.
Boys and girls develop reading skills through essentially the same cognitive and neural mechanisms. Despite a longstanding belief that dyslexia is more common in boys, research published in the Cambridge Handbook of Dyslexia and Dyscalculia found that behavioral differences between genders are few and small. Boys are more likely to be referred for evaluation, often because they’re more likely to show disruptive behavior in the classroom, but this reflects referral bias rather than a true biological difference in susceptibility.