ADHD Research Insights: Dyslexia, dyscalculia and subclinical symptoms

Hi, we are the ADHD Skills Lab podcast. My name is Skye. And my name is Sarah. And we will be your hosts chatting to you about practical ADHD strategies you can use, the research behind some of these strategies, as well as interviewing other professionals with ADHD about how they've developed skills and working through struggles in their lives. You might know us from Unconventional Organization, where we talk about this kind of stuff all day long. So we're super excited to have you along and we're going to chat through it together.

Today we have three very interesting papers to talk about. We're going to talk a little bit about ADHD and how it correlates or doesn't with dyslexia and dyscalculia, and then also a little bit about how it is distributed and how it looks in people in general. Could you have, for example, subclinical ADHD and that's what the other paper is going to look at. So lots of interesting ones to dive into today.

Comorbidity and causality among ADHD, dyslexia, and dyscalculia.

The first one we're going to have a look at is, co-morbidity and causality among ADHD dyslexia and dyscalculia. It was really cool to see dyscalculia in a paper because it's something that I personally have struggled with, but it's not as well known. Sarah, what's your sort of knowledge been of dyscalculia? Yeah, I have never heard of dyscalculia until, I think, until I met you, to be honest. You know, I'm one of those people that always sort of struggled with math, but Yeah, that was never something that we heard about, even in any of my psych classes. So it was really cool to read a paper on it. Yeah, I think it's very new. And it was a period where I, I mean, I only found out about it at the same time as I got tested for ADHD. I also got tested for dyscalculia. It was just preliminary testing, so they couldn't give me a final answer. But there was a heavily, heavily implied that basic maths was not my strong suit. Surprisingly didn't help. didn't have any issues with like later programming or using SPSS or any of those kind of statistical programs, but the basic math. So it's a learning disorder that affects a person's ability to do math, disrupts areas of the brain related to number and math related skills in the same way as dyslexia appears to disrupt areas related to reading. So these are two things that you might be thinking, oh, Oh, that's interesting. Or you might know somebody who has it, it might be something in your family. It's something that we talk about a lot being related to ADHD. And this paper wants to know and wants to look at why do ADHD dyslexia and dyscalculia co-occur at such a high rate. And before we go into how they did it, I'd like to talk a little bit about the two models that they said might be factors. They had a causal model. Which was to say that one of the reasons for this correlation could be that there's a direct relationship. So maybe dyslexia causes ADHD or ADHD causes dyscalculia. That was one possibility. The other one is what they call the correlated liability model, which says that maybe there's just an underlying genetic and environmental factors that push a person essentially in the direction. of both dyslexia or dyscalculia and ADHD, but they're not correlated. They're just all being expressed based on these underlying factors. Those were the two things they were looking at, and how did they do that? Do you want to go through that, Sarah? Sure. First of all, we're just going to throw it back to the basics. This is a cross-sectional longitudinal twins study, so study of twins. Their sample size was 19,000 twins. Wow. I've never seen that many twins. That's such a weird thing to say. I don't think they were all in the same place at the same time. That's like all the twins in the Netherlands. Like, yeah, you know what? I think actually it is. I looked up, I wanted to see where they got this sample from, because it is so large and it was just called the Netherlands twins registry. So I'm not sure if it is a massive research project that they do on twins, and if you bear twins then you must donate them to research. Anyway, people listening from the Netherlands, let us know. Yeah, tell us. Is that a thing that happens? Do you get paid? Yeah, all really interesting. While this study was technically longitudinal as they checked in on people twice, there was really only two and a half years in between. Again, they only checked in twice. ADHD diagnosis was self-report, parent survey. ADHD behavior was measured by a teacher report. They were also looking at things like grades, reading, spelling, math scores, that sort of thing. And then basically they defined that you have dyslexia if you score in the bottom 10% on the word fluency or spelling, and you had dyscalculia if you scored in the bottom 10% on... the math tests. Yeah, that's an interesting way of defining those two areas. I can see why they did that from a numbers perspective, and from the fact that often these things aren't actually tested properly. But the math test and how well you did, it's a bit of a narrow sample. I mean, as somebody who struggled with this, I definitely remember being very, very low in some of those basic tests when I was younger. But then sort of figuring out strategies and taking extra classes and doing things to improve my score, not because I was necessarily better at it, but just because that is a thing you can't do. Yeah, that's how a lot of us go undiagnosed. Yeah, yeah, essentially. So, yeah, I can see why they did that, but I definitely wouldn't say that that's a solid, you know, like these people definitely have dyslexia. There's no other reason why they would ever do bad on reading fluency or spelling. You know, good point, good point. So yeah, so again, they were looking to see whether there was, you know, is one thing causing the other? Is that maybe that there's just underlying factors? So what did they find Sarah? Well, I think the real smoking gun here is that children with ADHD in the sample were twice as likely as those without to have an additional disorder, dyslexia, dyscalculia in this case. And that's a really big point. I think it's really interesting. I have to say my first thought is So what you're saying is children with ADHD were twice as likely to be in the lower 10% of the math test or the English test, which isn't necessarily correlated, but it might be. And it is interesting as well, just because sometimes you might be bad at your spelling, not because you have dyslexia, but because you're just going so fast. And that was something that came up in my diagnosis was whether it was dyslexia or whether I just wasn't paying attention. So that might be a fact. I just wanted to flag that. But in terms of what they find, it was interesting because they found this indication that there was something going on. But then I think the number was, yeah, 86% of people just had one thing. So there was comorbidity and they did find that people with ADHD were twice as likely to have these additional comorbidities. But there was also a huge number of people who didn't have these comorbidities. I think that's worth mentioning. And they go on to mention it as well. If we're defining comorbidity in this case as scoring in the bottom 10%, speaking more on your point, there could be people who actually do have dyslexia or dyscalculia that just don't meet that criteria. Like maybe they got 20%. Yeah. You know? They're still probably struggling. But yeah, so I guess that's the problem with measuring it in that way. Yeah. That number suddenly doesn't seem to hold up as much as it did before. Yeah. We were talking about this and then as we were having this conversation, we started unpacking the paper for the sort of third time and pulling this out. Yeah. But what was it that made them think it's not causal and that it's this, these underlying genetic or environmental factors that are the reason for this correlation? So this is where it gets a little bit gobbledygook. But I'm going to start off by saying that the twins in this case is really important. So they look specifically at identical twin sets compared to fraternal twin sets. And by looking through all that data, they were able to see that it's actually shared genetic effects that are the main cause of co-morbidity among ADHD, dyslexia, and dyscalculia. They sort of go on to say that identical twin types. can be expected to have almost identical environmental influences as well. Whereas fraternal twins would have the same environmental setup, but share less of that DNA, that genetic component. So that's why the authors came away from this being like, yeah, the correlated liability model is what supports our data. Yeah, because identical twins are more likely to have that co-occurring ADHD dyslexia or dyscalculia. Yeah, it is interesting. I don't know if you have, this is a bit of an aside. They've done studies, I remember doing this back in the day in psychology classes, where they found that twins that had been separated for some reason, when they met again, they often like had named their dogs the same name and they had other things that were very, very similar. Yeah, I've read a lot of those stories. Yeah. I'd be interested to see like how much of that is, you know, still holds up today in terms of whether that was the case, but yeah, definitely very, very interesting. Okay, so in terms of like limitations and implications for the study, they didn't have any major limitations. Mostly it was the idea of the gap, the longitudinal study, which they kind of scrapped basically halfway through because they didn't have that real longitudinal effect. Yeah, so they were saying that like they ran the stuff through the causal model, statistical stuff, but it didn't have a good fit. So I'm not exactly sure what that means, but it didn't fit. So basically they were like, it's not causal. Yeah. But then they go on to say that we can't really use a causal model because there's not enough data points. So that's definitely a limitation for measuring that. Yeah. I don't know, but I imagine they would have done some kind of dot point and looked at the spread and seen if the spread was in the direction that it needs to be. Gotcha. Okay. So in terms of practical implications for the study. It's interesting. It basically indicates that if you have ADHD, you might want to check if you also have dyslexia and dyscalculia, especially if you are struggling with one of those areas. And surprisingly, you know, sometimes things will look different on different people. We have different ways of expressing something. We can mask, you know, we have our own experiences. So definitely worth having a look. And feeling like, okay, do I need extra support with this? Do I need extra ways of supporting this? Because similar to ADHD, it's not always about, I need to just work harder at this. It's more about understanding how your brain interprets math or interprets words and how to work with that. Absolutely. And then also if you're the parent of a child who has been diagnosed ADHD. familiarizing yourself with some of these other very common comorbidities could be a good use of your time. Yeah. Just get your kid the best supports. Yeah. Especially, you know, I don't know about dyscalculia. To be honest, when I was younger, it wasn't really something that was discussed. But dyslexia, even back when I was in school, long time ago, it was something that it's easier in some ways to get a diagnosis of things like dyslexia in school. There's more supports for it. It's not a bad time. to figure that stuff out. If you are an adult, and I say this as an adult, who's trying to figure out if they have something like this, there's not a lot of ways to do that. There's not a lot of supports for it, if it is the case. It might change from country to country, but that's sort of been my experience.

Neurocognitive Profile in Children with Attention Deficit/Hyperactivity Disorder and Dyslexia.

Okay, so the next paper is also similar. They wanted to look at the neurocognitive profile of children with ADHD and dyslexia. Basically, the purpose of the study. was to figure out where the deficits in ADHD and dyslexia, what was going on, and then compare them to control groups, which they called healthy control groups, but we're not going to do that because we don't like to. So what did they do to get this information, Sarah? How they did a bunch of tests. So first of all, they were just interested in just seeing what was going on in this ADHD and dyslexia. both separately, you have ADHD or you only have dyslexia, you have combined and then comparing that to a control group, they threw a bunch of tests of people to see what was going on. Do you want to take us through some of the more interesting ones? I don't think we can go through all of them. First, I'm going to start off by saying that this is taken from an outpatient sample, an outpatient psych facility. So they had 132 participants, 33 with dyslexia, 32 with ADHD, 37 with both, and 30 controls. So it was quite a well-rounded group. You could be included in this study if you had dyslexia and or ADHD, and an ID or above on the IQ scale. So since they were taken from outpatient psych clinics, the diagnosis was done by clinicians, which is always great. They excluded people with other comorbidities, you know, things like vision and hearing difficulties because they wouldn't have been able to do the tests. And then, which might have been an indication. Sorry. I'm just going back to our previous paper. I'm like, that might be why you've got like the lower 10% as well. If you had vision or hearing difficulties. Oh my goodness. Anyway, sorry. I'm going to stop talking about that. So the two tests that they used were the strip color test and. color and word test and the trail making test, which we've talked about other times. They also did something called a verbal cancellation test. So we'll get through those in a second, but they were specifically looking for your ability to control your body, like impulse control, being able to filter out extra stimuli, being able to sustain your attention over periods of time, even when faced with other stuff and then transitions. retaining info. Yeah, I think the first thing just to mention is that all the things you mentioned are things that people with ADHD are historically not very good at. So what we'd be looking for is to see that we're just struggling with all of these different areas with working memory, etc. And yeah, so they did a couple of tests. And do you want to give us just a quick rundown of what those three tests looked like? So the Stroop Color and Word test is basically they give you a color and it's letters they say red and maybe the color is blue and you either have to decide, okay, the color of that word is blue or you're supposed to read the word that it says. And sort of getting an incorrect versus a correct response in this case would be sort of sifting through the important stimuli. Yeah, no, definitely. And then we had the trail making. I believe that was the one where you had to connect the different pieces. Either they wanted you to go linearly like one, two, three, or maybe you had to connect only the even ones. You had to just whatever directions they gave you and do that thing. And then they would run multiple trials. Yeah. And you had to switch between numbers and letters as well. Right. Yes. So again, there was a bit of that switching. It was a bit of that ability to focus on a particular set. And then the one I know less about is the voice cancellation test, which sounds a bit Ominous. So the voice cancellation test is basically having to find the target word amongst other stimuli. So they basically like play a bunch of stuff for you and then push a button when you hear the word that they wanted you to find. Alternatively, they might have given you like a set to look through and then you like highlight the word again. Interesting. So again, it's like. Can you remove extraneous stimuli and just really focus on the one that you need to focus on? Can you prioritize? Well, can we? What were the results? Well, they found that overall, if you had ADHD or dyslexia, you perform significantly worse. If you had both. So if you had both ADHD and dyslexia, you perform significantly worse on all the tests. Yeah. Um, so, you know, not what we weren't expecting definitely a struggle with ADHD, but they did find that as well. It's important to note that while they did the worst, they didn't perform significantly worse compared to the ADHD only or the dyslexia only groups. So we're all sort of in this cognitive deficit boat together. ADHD only participants performed worse specifically on reaction inhibition. So like folding on. to your response until it's the right one. Mm-hmm. The visuospatial one, or I'm sorry, short-term memory test, which is the trail-making one. It's being able to remember a space. You know, like walking into a room and remembering what the layout was when you walk out of it and think about it. Yeah. People who are bad at that also struggle with maps. Interesting. And estimating distance and size. Yeah, so that was a particular struggle if you had only dyslexia, but like Sarah said, if you had both, it was a struggle as well. So we were all struggling with these executive functioning tasks. Yeah, so they found what they were looking for, essentially, which was that it was a difficulty for everybody. Before we go on to the limitations, I would like to know what you think the practical implications are of the study. Because it does... feel a little bit like a study to find a thing that everyone expected. You know, like, we've got a sample, let's do it. There's a paper to be had here. But what was the reason behind this study? They were trying to figure out a neuropsychological profile specific to dyslexia and ADHD. So basically what they wanted to do was they wanted to get a sense of what the actual struggles of ADHD and dyslexia were. I don't know whether it was, I mean, look, I haven't read all the papers by any means, but it is interesting. I feel like the neuropsychological profile has been somewhat mapped at this point. So it is interesting that they were looking for it anyway. But in terms of practical implications, it's more of a confirmation of what we already know, rather than a solution to any of those deficits basically. Yeah, definitely. I mean, this study doesn't do anything in the way of offering next steps or treatment suggestions or anything like that. Yeah, I think you're right. It's sort of just to combine the knowledge in one place. I'd be interested to see what they could do with your cognitive profile like that. Like, yeah, they could argue for more supports in a school setting or maybe something for assessments in the future. Yeah, because it is a very specific piece of information. So there is a space where you could say, OK, let's say this is it. And we've kind of got it on some level. You know, more studies need to be done to confirm. But, you know, we know now that people with ADHD and dyslexia struggle with these particular executive functioning deficits. It would be great to then talk about what supports can be put in the workplace or in the school space to help with that. You know, we do some of that already, but it would be great to see more of that. And just to get the awareness out that these things do coexist. Yeah, definitely. I think that's a really good reminder for both this study and the previous study is that, yeah, these things do coexist. And previously, I know we've talked about it before. There's been some resistance to the idea of things coexisting, like for example, ADHD and autism. Yeah, exactly. In terms of limitations, you know, they said there was a small sample size and also that they're working with a psychiatric sample. So symptoms generally are more severe. It's not the community sample that we saw in the previous study. And so the amount of people who struggle with these things and how they struggle might look a little bit different.

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Mechanisms of cognitive disinhibition explain individual differences in adult attention deficit hyperactivity disorder traits.

So our last paper and one that Sarah, you've done a bit more deeper dive into than I have, is looking at the mechanisms of cognitive disinhibition, explaining individual differences in ADHD traits. Essentially what they're looking at here is, are ADHD traits most optimally represented by a continuous and normally distributed phenotype? And I went to Abby, who if you've listened to previous episodes is our resident genetics expert and said, I, okay, I know what a phenotype is, but what does it mean that they're continuous and normally distributed? And basically it's how these traits are expressed. So how ADHD is expressed. But also the idea that there's so many different variations and ways that ADHD can come across that it might be that there is a large number of genetic factors and environmental factors involved, and this could be represented on a continuum, so a bell curve, and also might be seen as a continuum in general. So you might go from sort of moderate or minimal ADHD symptoms or traits to severe ADHD traits. So this introduces the idea of subclinical ADHD. It's a really interesting concept to think about ADHD symptoms in terms of like a bell curve, but just crash course for anyone who hated statistics and like doesn't wanna know what a bell curve is. You're gonna learn. It's basically just a bell shaped curve and the normal distribution means that most people are in the middle sort of. in the middle of the curve. And then there are people off to either side, but there are less people there. And it sort of tapers as you would expect from the shape of a bell. We talked about this a little bit earlier. I feel like this is sort of what they did with the autism diagnosis, although they usually represent that spectrum in like a pie graph, where like each symptom is sort of its own chunk. And then the severity. is sort of ranked in each section. I really like that. Anyway, really interesting. I would love to talk about how they did this though, because they did a really good job with this study. Their aim is sort of a little bit suspicious. That's fine. No, no, definitely. Go ahead. Tell me about this paper because I've read this paper, but I feel like I didn't get it as well as you did. So what did they do? It's a correlational study. You know, they're just looking at like things that are related. They had 650 adults, 329 of which, so about half of which were previously diagnosed with ADHD. This is also a clinical sample from a psych, you know, outpatient psych facility, but diagnosis was not corroborated by a clinician in this case. They basically just asked the people, have you ever been diagnosed with ADHD? And then they also had just their control group. So they were looking at ADHD traits and a cognitive battery assessment. So those were like the tests that they have them go through. So the ADHD traits were self-reports, basically like, how's your inattention? Are you organized? And then- Self-report, yeah. Yeah, I mean, basically they were just looking at like the symptoms spread again, trying to look at that continuum. And then the cognitive- battery assessment was basically, what was it, three or four different computer tests that were measuring things like, can you control your attention? Can you accurately gather and remember information? Can you revise? A very similar to our last paper. Yeah, exactly. Can you like keep track of and revise the information that you've taken in and things like that? So it was really interesting and Honestly, as I was reading this, they put these people through so many different trials of each one. It wasn't like you could just do it one time and you were done. Like I want to know how many hours were put in on these tests. They don't say. Yeah. Yeah, they had so many computer games, bounty hunters, shoot the robber, caravan. Some of these look a little bit like when you're trying to log in to something and it says like you can log in, but first you have to tell me how many stairs are in these pictures. Yeah. But you know what, they were probably really super basic games. I'm picturing like Oregon Trail version of graphics and things like that. So yeah, let's talk about it. So the bounty hunter game was looking for can you control your attention? So they would say you have to shoot the robber, not the cop, and you'd earn or lose money based on your accuracy. I'm guessing we didn't do great at that. sort of changed a bunch through each different trial. They're really trying to mess with you. The caravan spotter was interesting. So it was like they showed you a picture, but it was super pixelated, like couldn't make it out. And then gradually it would sort of reveal itself to you and you'd have to pick what the image showed correctly as quickly as possible. And you'd sort of earn or lose points based on how well you did that. And then the prospector's gamble was really super confusing. So it worked. on me. So basically, from what I could understand, basically, you had to pick between two guys, like who's going to find the most gold? And they would say like, well, this one's luckier. And then sort of each trial, it would revise like which person is luckier. it said they would give you false reinforcement. So like tell you were right, even if you were wrong and see if you like pick up on that, and things like that. It was a very cruel task to trying to measure your ability to make decisions and process and adapt to feedback, even when it's wrong. That's rough. Very cool. Yeah. Man, these poor people, I hope they got like something good out of this. Yeah, compensated. That's what I mean to say. Yeah. Okay, so They put them through all these tests. Sounds like it was a long afternoon. What did they find? Yeah. So they ran a ton of different statistical models. They were using Bainsey and anyway, it doesn't matter. Um, sort of a bunch of different statistical models. And basically what they really wanted to identify was to what degree each of those cognitive functions contributed to the expression of ADHD traits. So they were looking basically at the self-report data that people gave and then the results of these tests just to see how it all lined up basically. And they looked at it from different ways. And what they found was that while yes, these cognitive measures did explain some of the variation among the participants ADHD traits, it actually only explained under 16% of the variance. in how people experience ADHD symptoms. So that was really interesting because it sort of was like a throwback to last week's conversation that we had with Abby, where we talked about how genetic expression accounts for an estimated one third of our ADHD. In terms of what that means, maybe for people who didn't listen to last week's, what would that mean? Yeah, so basically what we were talking about last week was that your genes are responsible. You know, they sort of send messages to our body to be something, do something. And they've actually found that basically one third of the genes in your body are at play in your expression of ADHD. So like if you struggle more with hyperactivity, that's going to be coded in your genes. sort of if you struggle more with the impulsivity or the inattention, like that's going to just be different genes working together to express that, to basically create you and your behavior. And the cognitive tests that they did here on attention and set switching, information gathering, that only captures 16% of the picture. So basically there's a lot more to understand you know how people's ADHD expresses itself in real life. Like what does that mean? Like has anybody asked you ever asked you like oh well what symptoms of ADHD are you struggling with you know and you're likely to say oh well you know I lose like I lose track of time and stuff like that and then they'll say no but like how does that affect you in real life? Oh well I snooze my alarm 20 times. Yeah you know 100% yeah. Oh I have to close all my notifications without looking at them. Like those are real things. but the underlying issue is a cognitive dysfunction. Yeah. It's interesting. We talk about this genetic factors and it is interesting because we think, oh, this is just who I am. This is just a problem that I have. We never think this is something that could be being expressed in our DNA. It's interesting to think about this from a genetic perspective. It's something I haven't really done before. Yeah. That's a really good point. Neither have I. Yeah. I'm trying to integrate it now, alive on air. I mean, that's like a whole other level of self-acceptance, really, which is something that we struggle with. Yeah, 100%. So in terms of kind of the implications of this study, it was interesting that they did a study of discussing the possibility that you could have subclinical ADHD basically, and what that would look like in terms of that. normal distribution curve. What were the other kind of practical implications of the study? One of the implications was that they wanted to figure out whether they could discern earlier intervention. So they were sort of saying, look, if somebody doesn't meet the clinical thresholds for ADHD, but we know enough about the spectrum of ADHD that we can identify that they could meet those thresholds in the future, would that then allow us to identify and support them? earlier. I mean, there's sort of arguing in that case that their ADHD might get worse. Preventative mental health. Yeah. I don't know whether that is an accurate way of discussing it. It's how they discussed it. But that was one of the practical implications. I think it ties into also the variability of symptoms over the lifespan. So we've talked about this in another paper where basically over the course of time, you might struggle more with certain symptoms than others. Sometimes you might not need really any supports at all. And sometimes you might need all the supports. So I think it kind of makes sense that like the symptomology would exist on a spectrum like this. And definitely identifying people who are at risk would for sure help. All it takes is your biology to change a little bit or like a certain gene to get turned on. And now you're experiencing something new and challenging. Maybe you like lose your whole support structure. So now you're struggling. Yeah, I love that conversation. That's why I was so excited by this study. Yeah, yeah, definitely. Definitely. I know very, very interesting as are all of these studies actually, um, this week, very, very interesting studies, sort of not necessarily giving us a solution this week, but more tapping into a bit of the why we are the way we are, what are we, what is it related to? Yeah. So very, very interesting. Is there anything else you wanted to mention about these studies before we head off today, Sarah? Yeah, I think I'm just going to say that ADHD isn't all cognitive. Not everything about ADHD is going to be like, oh, my working memory is bad or my time blindness is bad. You know, I struggle to transition. And this study in particular, you know, only 16% explained the symptoms. So that just shows how much more there is to ADHD than struggling to control attention, et cetera. And I think that's a great reminder for everyone. Yeah, definitely. Definitely something to keep thinking about and keep mapping out. Awesome. Well, really good to chat about these. Thanks for coming along. If you have any thoughts, feel free to email us. Otherwise we'll see you next week. 

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