Is dyslexia genetic?

I’m a graduate student in linguistics. I have a degree in English literature. I love reading, writing and books with the fiery passion of a thousand suns. And I am dyslexic. While I was very successfully academically in secondary and higher education, let’s just say that primary school was… rough. I’ve failed enough spelling tests that I could wallpaper a small room with them. At this point I’m a fluent reader, mainly because no one’s asking me to read things without context. (For an interesting experimental look at the effects of world-knowledge and context on reading, I’d recommend Paul Kolers 1970 article, “Three stages of reading”.) These days, language processing problems tend to be flashes in the pan rather than a constant barrier I’m pushing against. I tend to confused “cloaca” and “cochlea”, for example, and I feel like I use “etymology” and “entomology” correctly at chance. But still, it would be nice to know that my years of suffering in primary school were due to genetic causes and not because I was “dumber” or “lazier” than other kids. And recent research does seem to support that: it looks like dyslexia probably is genetic.

First off, a couple caveats. Dyslexia is an educational diagnosis. There’s a pretty extensive battery of tests, any of which may be used to diagnose dyslexia. The International Dyslexia Association defines dyslexia thusly:

It is characterized by difficulties with accurate and / or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge.

Which sounds pretty standard, right? But! There are a number of underlying causes that might lead to this. One obvious one is an undiagnosed hearing problem. Someone who only has access to part of the speech signal will probably display all of these symptoms. Or someone in an English-only environment who speaks, say, Kola, as their home language. It’s hard to learn that ‘p’ means /p/ if your language doesn’t have that sound. Of course, educators know that these things affect reading ability. But there are also a number of underlying mental processes that might lead to a diagnosis of dyslexia, which may or may not be related to each other but are all almost certainly genetic. Let’s look at a couple of them.

• Phonological processing. I’ve talked a little bit about phonology before. Basically, someone with phonological disorder has a hard time with language sounds specifically. For example, they may have difficulty with rhyming tasks, or figuring out how many sounds are in a word. And this does seem to have a neurological compontent. One study shows that, when children with dyslexia were asked to come up with letters that rhymed, they did not show activity in the Temporoparietal junction, unlike their non-dyslexic peers. Among other things, the Temporoparietal junction plays a role in interpreting sequences of events.
• Auditory processing. Auditory processing difficulties aren’t necessarily linguistic in nature. Someone who has difficulty processing sounds may be tone deaf, for example, unable to tell whether two notes are the same or different. For dyslexics, this tends to surface as difficulty with sounds that occur very quickly. And there’s pretty much no sounds that humans need to process more quickly than speech sounds. A flap, for example, lasts around 20 milliseconds. To put that in perspective, that’s about 15 times slower than a fast blink. And it looks like there’s a genetic cause for these auditory processing problems: dyslexic brains have a localized asymmetry in their neurons. They also have more, and smaller neurons.
• Sequential processing. For me, this is probably the most interesting. Sequential processing isn’t limited to language. It had to do with doing or perceiving things in the correct order. So, for example, if I gave you all the steps for baking a cake in the wrong order, you’d need to use sequential processing to put them in the correct order. And there’s been some really interesting work done, mainly by Beate Peter at the University of Washington (represent!) that suggests that there is a single genetic cause responsible for a number of rapid sequential processing task, and one of the effects of an abnormality in this gene is dyslexia. But people with this mutation also tend to be bad at, for example, touching each of their fingers to their thumb in order. 
  
• Being a dude. Ok, this one is a little shakier, but depending on who you listen to, dyslexia is either equally common men and women, 4 to 5 times more common in men or 2 to 3 times more common in men. This may be due to structural differences, since it seems that male dyslexics have less gray matter in language processing centers, whereas females have less gray matter in sensing and motor processing areas. Or the difference could be due to the fact that estrogen does very good things for your brain, especially after traumatic injury. I include it here because sex is genetic (duh) and seems to (maybe, kinda, sorta) have an effect on dyslexia.

Long story short, there’s been quite a bit of work done on the genetics of dyslexia and the evidence points to a probably genetic common cause. Which in some ways is really exciting! That means that we can predict better who will have learning difficulties and work to provide them with additional tutoring and help. And it also means that some reading difficulties are due to anatomy and genes. If you’re dyslexic, it’s because you’re wired that way, and not because your parents did or didn’t do something (well, other than contribute your genetic material, obvi) or because you didn’t try hard enough. I really wish I could go back in time and tell that to my younger self after I completely failed yet another spelling test, even though I’d copied the words a hundred times each. 

But the genetic underpinning of dyslexia might also seem like a bad thing. After all, if dyslexia is genetic, does that mean that children with reading difficulties will just never get over them? Not at all! I don’t have space here to talk about the sort of interventions and treatments that can help dyslectics. (Perhaps I’ll write a future post on the subject.) Suffice to say, the dyslexic brain can learn to compensate and adapt over time. Like I said above, I’m currently a very fluent reader. And dyslexia can be a good thing. The same skills that can make learning to read hard can make you very, very good at picking out one odd thing in a large group, or at surveying a large quantity of visual information quickly — even if you only see it out of the corner of your eye. For example, I am freakishly good at finding four-leaf clovers. In high school, I collected thousands of them just while doing chores around the farm. And that’s not the only advantage. I’d recommend the Dyslexic Advantage (it’s written for a non-scientific audience) if you’re interested in learning more about the benefits of dyslexia. The authors point out that dyslectics are very good at making connections between things, and suggest that they enjoy an advantage when reasoning spatially, narratively, about related but unconnected things (like metaphors) or with incomplete or dynamic information.

The current research suggests pretty strongly that dyslexia is something you’re born with. And even though it might make some parts of your school career very difficult, it won’t stop you from thriving. It might even end up helping you later on in life.