Short Wave - Have a Stutter? It Could Be Inherited

Episode Date: September 3, 2025

For a long time, scientists have suspected that stuttering — a common speech condition that affects an estimated 1 in every 100 people — could be heritable. Despite how common it is, it's still a remarkably understudied condition. Geneticists Piper Below and Dillon Pruett were determined to fix that. With the help of 23andMe data, they recently identified 57 genetic regions linked to stuttering in the human genome. Their findings represent a new breakthrough in how researchers think about speech conditions, genetics and the conditions that are linked to them. They're what some are calling a "quantum leap" in the field.Interested in more human biology and genetics episodes? Email us your question at [e-mail] to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, shortwaver's Emily Kwong here. And today we're going to meet Dylan Pruitt, a genetics researcher at Florida State University in the School of Communication Sciences and Disorders. And the particular condition Dylan studies, it's been with him most of his life. I started stuttering around age three

throughout elementary school, was in speech therapy. And estimated one in 100 people have a stop. according to the National Institute of Health. That's 3 million Americans, but it is still an understudied condition. Dylan told us that even in college, there wasn't a lot of robust scientific knowledge about stuttering, what causes it, and why some people who start stuttering in childhood eventually stop, while others do not. I had kind of heard like, oh, there was some new studies that were looking at genetics of stuttering and reached out to a professional. and asked some questions, and he was like, you know, honestly, this is a very new area.

I don't know a lot about it, but it's an area that needs a lot more research. So Dylan decided this was it. This was the research he wanted to pursue. And while it was frustrating that there were very few answers. It was another way kind of inspiring, realizing that I could take action and pursue this field of study and really contribute to the field. Alongside geneticist Piper B. Loe and her team of researchers at Vanderbilt University, Dylan recently released a paper that is making waves within the field.

Published in the journal Nature Genetics, the study identifies 57 genetic regions linked to stuttering and what other conditions stuttering may be related to. Today on the show, a breakthrough in stuttering research. How a simple 23-and-me survey led to new genetic research, insights and directly challenges misconceptions about what causes stuttering in the first place. I'm Emily Kwong and you're listening to Shortwave, the science podcast from NPR. Okay, so to learn about the genetics of stuttering, I called it both Piper Bilo and Dylan Pruitt, who worked on this study.

I started by asking them, okay, you guys, what's the main research question you were hoping to answer? Yeah, there has been an awareness for a very long time that stuttering is a trait that is very enriched in families. meaning that if you are a person who stutters, you have a much higher likelihood of having a second or third individual in your family who also stutters, then you would expect by chance. But another really common explanation is that there's some environmental exposure that is common to everyone within a family or within a household. And so in this case, we were really interested in tackling this question of whether or, or not, we see this clustering of stuttering within families as a result of genetic factors. Yeah. And so we were very excited to be able to try to pinpoint the specific genes and variants

that were contributing. And to pursue this question, you needed a massive data set that connected stuttering to genetics. You can't just like find one out there with a search on the internet. Where did you get one? Yeah, that's a great question. So we have been. been working on this question for, gosh, 15, 20 years now. But after years and years and years, had only amassed about 1,500 or 2,000 people who stuttered. It became apparent to me that in order to give this research the same sort of power for discovery as what we see being published every day for traits like diabetes or Alzheimer's disease or obesity, we would need to find a biobank that we could tap into that could provide both data on stuttering and genetic

information at a really large scale. And it was so exciting when a colleague of mine sent me a message. She was at a research conference. She saw a poster being presented that had a snapshot of some questions from the 23 and Me survey for people that can send to research. This being the genetic ancestry testing service for people to figure out, like, where are their families from? Secret cousins they never knew they had kind of stuff. Exactly. Exactly. So this direct-to-consumer genetic testing company, 23 and me, had a question on their survey that was, you know, have you ever had a stutter or a stammer? It's pretty incredible. You really got the granddaddy of biobanks when it comes to stuttering research. No, really. And I understand that this study, what also makes it unique in addition to having access to 1.1 million users via 23 and me who reported whether they had ever had a stutter or had not.

What also makes your study unique is that it was a genome-wide association study. Dylan, what does that mean a genome-wide association study? So it's a approach that is looking at areas of the research. the genome that are kind of known to vary and then analyzing them to see if they are associated with a trade. You know, when we look at everybody that has this trade, everybody that does not have this trait, what are the handful of variants that are associated with that trait? Of like genetic variance? Correct, correct. So you're saying that through this process you'd be able to see every single gene that's potentially linked to stuttering. Exactly right. Exactly

right. And that led us to hypothesize maybe this is a trait that is more like the diabetes, obesity, height, kinds of traits. And the genetic architecture of those have all been shown to be highly polymorphic, meaning there's a large number of variants from all across the genome that all, you know, some might increase your risk a little bit, others might decrease your risk a little bit. You can almost think of it like you're putting sand on either side of a teeter-totter and eventually, If one side becomes heavy enough, then it flips and, you know, you have a higher risk for this trait. And indeed, what we found was completely consistent with that hypothesis. We ended up revealing nearly 60 genomic regions across the whole human genome that were, you know, contributing small bits of additional risk of developing a stutter.

That must have been so gratifying. Were any genes real standouts for you as like playing an outsized? role in contributing to the emergence of stuttering? Yes, absolutely. The day we got the summary results released by 23 and me and transferred over to us, and I opened the file to look at the results, I actually had to sit down because the number one gene that emerged from our study was this gene, VRK2. And the reason why that made me actually took my breath away was because that Gene had just come out a few months prior as the number one hit in a very large analysis of rhythm ability, people's ability to clap to a beat. And so this was the first time anybody

actually had found a shared genetic underpinning, underlying both developmental stuttering and this sort of rhythmicity, rhythm and musicality phenotype or trait. Yeah, I mean, I think it was really intriguing and not only was it found as a top hit in the musical beat synchronization, but it was also the top hit in a couple of other independent studies that were looking at language as well. And so knowing that speech and language is so intricately tied and knowing that essentially the primary deficit in the, And stuttering is really the timing of speech. It really blew me away. I think this gives us a really unique direction to explore. I love this discovery because it suggests one of the potential genetic causes is a rhythmic difference.

Like just the musicality of someone's speech is different. Not bad. Just different. Yeah. Yeah. And I think that when you. you are caught in a moment of stuttering, it does feel like the inability to move forward or to push past a sound. And so having these external timing mechanisms that can increase fluency, that might be generating some external cue that is lacking internally to a degree or is misaligned to a degree.

Okay. Are there any other notable genetic tidbits that emerged from this study, any other associations beyond misalignment around rhythm? Yeah. We observed positive correlation in males and females with depression. We also found correlations with autism and negative correlations with the beat synchronized. And so those are all features that we sometimes see associated with stuttering clinically. And so the genetic correlation is showing that there might be a genetic basis for this clinical associations that we see. Do you think, do you now think there might be different subtypes of stuttering? Oh, so there are different subtypes of stuttering. And this actually leads me back to what I was alluding to before about these really fascinating sex differences. So when kids turn, you know, about three, the onset of stuttering is approximately equal between girls and boys. But what's

really interesting is that 80% of kids who stutter go on to recover, whether through therapy or spontaneous recovery. But most of those that recover are... girls. And if you don't recover as a child, you are very likely to stutter for life. And this is what we call a persistent stutter versus a recovered stutter, which typically happens in fairly early childhood. So are you saying the subtypes fall along biological sex lines? Yeah. Yeah, they do. And we don't understand why. You know, what is different about girls and boys, especially as they go through this transition around age seven or eight that explains this difference. Dylan, going back to you, why does this research matter so much? And how can it support people

who stutter? I think that for decades, we've been trying to look at the stuttering puzzle by looking at the pieces in isolation. And so that's the behavioral patterns, the neural circuits for speech, the role of language. And each of these have given us valuable clues, but they haven't been able to connect the dots. And so one of my hopes is that genetics could offer a mechanistic framework or a way to see how these kind of separate domains are all interconnected and shaped by the underlying biology. Yeah, that's so interesting. Well, I got to ask you this then too. How do you hope this research then shapes treatment. Dylan, is this about finding a cure for stuttering? Yeah, I don't really see our research as being about finding a cure for stuttering.

I view our work is really about demystifying it. I think that stuttering is a beautiful and, in my view, underappreciated example of neurodiversity. And so our work helps us understand the genetic script behind that diversity. I think that instead of a one-size-fits-all approach, perhaps we could move towards more personalized support strategies to tailor towards an individual's unique neurobiology. And this can be really powerful and maybe empowering for people who stutter and their families.

Yeah, absolutely. I don't think of this as a discovery that is sort of closing the door on a chapter in stuttering. I feel like we just threw every door and window open. Right. This is us approaching a starting line, not a finish line. Dylan and Piper, thank you so much for talking to us. Thank you. It's really been a pleasure. Yeah, it's been really great to talk to you. This episode was produced by Hannah Chin and edited by our showrunner Rebecca Ramirez. Tyler Jones checked the facts. Coyce Lee was the audio engineer.

Special thanks to John Hamilton. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Emily Kwong. Thank you for listening to Shorewave from NPR.