Even though my son has both these diagnoses (amongst others) I’m not asking this rhetorically: is it correct that someone can have both autism and dyslexia? The answer to this depends on a variety of considerations, including understanding the changes in diagnostic criteria for both autism and dyslexia over time, and understanding the challenges that autism creates in the areas of literacy and how those differ from dyslexia challenges. I’m not a diagnostician, just a mum of a child who has been given both labels, who wanted to better understand this sort of statement: “Officially … ASD is an exclusionary criterion for diagnosis of dyslexia and vice versa“. So, I decided to dig deeper into their cooccurrence / comorbidity, and see if I could find a consensus.
I want to briefly start by pointing out something that I do think is significant: my son’s autism diagnosis came first and his autism diagnostician (a developmental paediatrician) was the first to officially suggest he may have dyslexia, so she clearly didn’t see the two as exclusionary; and then the educational psychologist who ended up diagnosing him with dyslexia was fully aware of his existing autism diagnosis. So, we have two experts in their various diagnosis fields who are clearly of the view that these two conditions can co-exist and indeed did co-exist in my son.
Why then do we have such a statement as I shared above, about them being officially viewed as exclusionary (there were other reputable sources which made the same claim)?
In part this reflects changing diagnostic criteria. The latest diagnostic criteria for dyslexia were updated in 2013 for the DSM-5 and 2019 for the ICD-11 (the two most popular manuals for defining such conditions). Under the DSM-5, dyslexia comes under the term “Specific Learning Disorder”, and under the ICD-11, it’s “Developmental Learning Disorder.” It is understood that both of these capture dyslexia (amongst other conditions) and when you read through the descriptions you can see significant cross-over. Part of the cross-over is that both want to make sure that the issues present are not due to a neurological disorder or intellectual disability. Does this mean autism is an exclusionary condition?
Not necessarily. I believe it becomes a matter of professional judgement, which I’ll try to explain: Autism doesn’t present hand-in-hand with difficulties in reading, in fact some autistics have hyperlexia, where they can decode/read well beyond their years but may not be able to comprehend what they are reading. Reading comprehension is a recognised issue for autistics, especially in the area of fiction, even for those who are “high-functioning, ” as it requires dealing with non-literal language and sub-texts and similar social-based language challenges. But there is another aspect of how autism can impact on literacy abilities that seems to be of crucial importance here: if the autism so severely affects the child that it is interfering significantly with their ability to learn, then the cause of not being able to read may indeed be rooted in the autism rather than something that can be independently identified as dyslexia. This is my layman’s understanding of the relevance of autism to a dyslexia diagnosis and the complexities it brings, based on what I’ve been able to find on the issue, and this brings us to the next point:
One of the most common statements I came across in trying to get my head around this, was that there has been very little research done into the comorbidity of autism and dyslexia. A couple of reasons given for this do make sense: (1) if you want to study dyslexia, you should remove those with autism from the study because it would complicate the results and the interpretation of the results, and vice versa for dyslexia impacting on studies about autism, and (2) both of the conditions happen across a spectrum of severity and without clear cut-off marks, complicating their mutual comparison and finding participants that you can draw clear results from. Trying to study the two together certainly poses challenges.
This is not to say there are no studies on the comorbidity. I have found references to the comorbidity of autism and dyslexia that range from 6% (in a 2006 and 2018 study) to 30% (in a 2010 study). Given that the other most common statement I’ve come across on comorbidity is that they can co-occur but would do so infrequently, it seems the 6% figure is more likely to be the accurate one (if we’re going for a consensus approach here).
Both dyslexia and autism, as distinct conditions, are well-known to have high comorbidities with a range of other conditions. Depending on what you include as a psychiatric or medical condition (and depending on the study and whichever diagnostic criteria was being used) dyslexia comorbidity rates sit around 50-60% (with a large chunk of that being ADHD) and autism comorbidity rates also sit around 50-75% (and up to about 88% if you include some more controversial conditions such as Sensory Processing Disorder on the list). The spectrum aspects and shifting definitions of these two conditions, dyslexia and autism, and the high comorbidities that come with both (albeit with other conditions) with the added complexity that brings to teasing apart what condition is causing what symptom, add so this picture of why it is hard to get clear guidance on how linked or separate they are from each other.
So, where does all this get us? I’ll give you my view, and I’d certainly be interested to hear yours: The two can co-exist, and they bring different sets of challenges that can generally be distinguished, but there is enough potential cross-over areas (such as autism’s impact on learning and impact on comprehension) that a diagnosis would have to be done very clearly with the two in mind, to avoid misdiagnoses. Here is New Zealand (I don’t know if it’s the same overseas but I suspect it is) you need to see different professionals for the two diagnoses, so when choosing a diagnostician it will be important to find someone with a good understanding of the other (confirmed or suspected) diagnosis.
Some of the readings I found useful towards writing this post:
Dyslexia Diagnosis Criteria (DSM and ICD)