What Causes Dyslexia? An Overview of 5 Theories

As you may know, dyslexia is a learning disability that causes reading and language difficulties. These difficulties are the result of the way the dyslexic brain processes graphic symbols (letters) in connection to their sounds (phonemes) in a given language.

Although many of the symptoms of dyslexia have been discovered, it still remains unclear what causes dyslexia. However, there are several theories which help explain the origin of this condition. Most researchers believe dyslexia is caused by a combination of these theories, but the exact combination or specific cause is yet to be discovered.

1. Brain Development

dyslexic brainSome researchers have found clusters of cells in the dyslexic brain that did not make it to the same location they are found in the non-dyslexic brain. In the non-dyslexic brain these cells are found primarily in the left side of the brain, the same area used dominantly for reading and language tasks, thus it is believed that these cell misplacements make it difficult for dyslexics to process language tasks.

2. Wiring of the Brain

In connection with the cell misplacement in the first theory, another theory is that dyslexia is caused by a unique wiring in the brain. Dyslexics have been found to have strong activity in the right side of their brain. Because of the strength of their right brain, they engage this area while performing language tasks. However, as mentioned before, language tasks are typically and most efficiently performed in the left side of the brain. Thus, the wiring of the dyslexic brain is often prescribed as the cause of dyslexia.

3. Genetic Inheritance

These differences in brain structure and development are often found to be generational. Not every child of someone with dyslexia is dyslexic, but it is common for a dyslexic to have a family history of the condition. Also, dyslexia has been found to correlate to left-handedness. Just because someone is left-handed does not mean they are dyslexic, but it has been found that about half of the family members of a dyslexic are commonly left handed.

4. Hearing Problems at a Young Age

Another theory is that dyslexia is caused by hearing problems while a child’s brain is still developing and learning language. Early colds and other infections can cause a child’s ears to get blocked on occasion and thus impair their hearing. By not having clear hearing, a child can have a difficulty learning the sounds of language (phonemic awareness). This early learning period of the sounds of language is very important for developing effective language skills in the future. This problem can be resolved if caught at an early stage. There are treatments available, the most common being a tiny tube that is inserted into the child’s ear to prevent it from getting blocked again. 

evolutionary theory of dyslexia5. Evolutionary Perspective

Lastly, there is a theory that dyslexia is a result of evolution. The theorists supporting this idea claim that reading is an unnatural act that was not required in the past, and has only been used in the recent past. Most societies have been reading for less than 100 years, and thus not all humans have evolved the ability.


Although the experts are still not exactly sure what the cause of dyslexia is, there is evermore research that is being conducted and the cause is still being sought after.

Let us know what theory you agree with. We would love to hear your thoughts!


Bradford, John. "What Causes Dyslexia?"

Kaufman, Lorna N., Ph.D., and Pamela Hook, Ph.D. "The Dyslexia Puzzle: Putting the Pieces Together."

"Theories of Dyslexia." http://en.wikipedia.org/wiki/Theories_of_dyslexia

"What Causes Dyslexia." http://www.the-dyslexia-center.com/what-causes-dyslexia.htm

free dyslexia webinar


  • Luqman Michel

    I am sorry but I completely disagree with your first paragraph where you say the following:"As you may know, dyslexia is a learning disability that causes reading and language difficulties." I teach dyslexic children and I believe that dyslexic children are just wired in a slightly different way, say, like a left hander. There was a time when left handers were treated as disabled.But today we know many left handers who are just as good if not better than right handers. A dyslexic just learns in a different way than a non dyslexic. If they are taught in a way appropriate for them they learn just as fast as any other.(They are like left handers in a right handers world.) I teach dyslexics 3 languages and they can read in 2 languages as fluently as any other kid can. These two languages use the same 26 alphabets as the English language.As such how can it be said that dyslexics have a reading and language problem, unless you take English as the only language in the world.But even English can be taught to them if taught in a proper manner. To say that, "These difficulties are the result of dyslexics brain impaired ability to process graphic symbols (letters) in connection to their sounds (phonemes) in a given language." is also incorrect. All my students do not have a problem with grapheme and phoneme when it comes to Malay and Romanized Mandarin. They also do not have a problem with grapheme and phoneme when it comes to reading phonologically correct English words. Their minds shut down when the grapheme and phoneme do not make sense.If the different phonemes of the English alphabets are clearly explained to a dyslexic child he can and will read as fluently as any other kid. How many teachers actually teach a child that the letter 'a' consists of 6 phonemes (may be more) and that the grapheme 'e' represents at least 7 phonemes.This is why I have seen my dyslexic students giving a blank look when I teach them "A cat" after having taught them the words bat, cat, fat, hat, mat, pat, rat and sat which they learn with ease. (refer my lessons in my blog in March). They are puzzled with "A cat" because the phoneme of the "A" in A cat is different from the phoneme of 'a' in cat. The children however, can accept and understand and continue learning when I tell them that the letter 'a' has more than one phoneme unlike in Malay and Mandarin. The same goes for Finnish, Tamil and many other orthographically consistent languages. Parents with dyslexic children are welcome to use my lessons in my blog to teach their dyslexic children. They have proven effective with my own students and many parents from many parts of the world have also written to say that they are grateful for the lessons.The lessons are all free of charge. I believe that instead of wasting valuable resources in finding out what causes dyslexia (just like it would be a waste of time finding out why left handers use their left hand more efficiently)it would make more sense in finding out how to teach a dyslexic. Instead of fighting over a choice between "whole word" and phonics use both like I have used in my lessons. By using both anyone can learn to read simple sentences from the first lesson. Thank you and kind regards, Luqman Michel http://www.parentingdyslexia.com

  • angela

    We appreciate your opinion. Although you disagree with the definitions of dyslexia used, our program does support your findings. For example our program gives teachers a systematic approach for teaching the very concept you highlighted: "How many teachers actually teach a child that the letter 'a' consists of 6 phonemes (maybe more) and that the grapheme 'e' represents at least 7 phonemes." Our program provides teachers and individuals concrete strategies for teaching and learning these sound relationships. That is why our program does work for dyslexics. I admire your distaste for the definition of dyslexia as a learning disability. The more I learn about dyslexia, the more I admire their mind and abilities and know that they have a lot of valuable skills and that they do just need to be taught in a different way to overcome their reading difficulties.

  • Allan Hytowitz

    While there may still not be a definitive answer as to the cause of visual dyslexia-type symptoms, we seem to discovered a chromatic perception test that definitively correlates as to who does and does not have visual dyslexia-type symptoms.

    The test is free at http://www.dyop.org/color.htm or specifically at http://www.dyop.org/documents/ColorScreening.html.

    We would love to have feedback from those who know they have dyslexia and those who do not as to their responses in preferentially being more able to see the Green-on-White Dyop™ images (non-dyslexic) or the Blue-on-Black Dyop™ images (indicating dyslexia-type symptoms).

    Please send your observations and results to Allan@Dyop.org.

    What we have discovered so far is that not only IS the Dyop™ color/contrast test successful in screening for visual dyslexia-type symptoms, but a lot of the "false positives" are from people who have dyslexia-type symptoms and have managed to overcome them using self-developed methods similar to the Orton-Gillingham process.

    Your feedback would be greatly appreciated.

  • Kildonan School

    Teaching students with dyslexia is no easy task. I do agree with Luqman, however, about dyslexic children comprehending foreign languages at the same level of their peers.

  • Stephanie Pauline

    The idea that those with dyslexia (me) are somehow less evolved is ludicrous. A non-dyslexic came up with that one. I simply think differently than others. Turn things over in my mind differently and need more holistic information to absorb and retain knowledge. I have found that, in more areas than just reading, (which was a real struggle for me until I was identified and the teaching process was tailored to my way) I need to UNDERSTAND, not merely memorize and regurgitate. I want to be able to synergize the principles BEHIND any new information with my prior knowledge base so I can effectively use them to enable my own creative impulses. So often early education doesn't offer THAT kind of learning. I've had to overcome an insatiable need to know why - for me as a child if you couldn't tell me why - you were no longer perceived as credible and the information you were giving was not helpful to me. I was simply different in the way I perceived and integrated the whole. Also, the diagram you show above of the brain is named "nonimpaired" and then "dyslexic" - again labeled by a non-dyslexic I surmise. Please. What makes people so blindly arrogant? My ability to write with my left hand, cut vegetables with my right, create fluidly - seeing endless possibilities, and then bring a vision to pass through project management is directly related to my so-called impairment. I have limits as does everyone, (like having to spell check this every fourth sentence) and some of mine are more unique than perhaps some others, but that only means that the ways I am LESS limited than YOU are just as unique, and therefore truly valuable. I am different. I am not disabled. The relationship between my left hemisphere and my right is different than yours. I would say - it is better. So now whose arrogant? I reject any notion that we can't process information and verbalize through rhyme too. Things may take us longer, but once we overcome the way we are being taught then we can embrace and use all these seeming weaknesses as wonderful expressions. I am a songwriter and I LOVE words. Ridiculous arbitrary spelling rules don't love ME, but I love words and mostly the associations I can impart to you through them when I string them together well with an inspiring thought. So glad people who taught me didn't regard me as disabled, or less evolved. So glad my tutor in kindergarten and 1st grade, who sat beside me day in and day out, answered my many why's tirelessly. So thankful she let her finger follow along beneath every letter and let the calm, lilt of her voice sound each syllable as slowly as I needed her to, over and over…until my voice replaced hers. Can you hear it now?

  • angela

    Thanks for adding your perspective Stephanie! I absolutely agree that those with dyslexia are extremely gifted and intelligent... and the fact that their intelligence and viewpoint is different from the majority of individuals is a huge gift to society!

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Oct 04 2010

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