(SOUNDBITE OF MUSIC)
EMILY KWONG, BYLINE: You're listening to SHORT WAVE...
(SOUNDBITE OF MUSIC)
KWONG: ...From NPR.
REGINA BARBER, HOST:
Identical twins are identical, right? Well, not completely. And especially not when it comes to autism spectrum disorder. Here to chat about this is NPR's resident brainophile (ph), Jon Hamilton. Hey, Jon.
JON HAMILTON, BYLINE: Hey, Gina.
BARBER: OK. So I understand you've been reporting on autistic twins as part of the NPR series on The Science of Siblings.
HAMILTON: I have. And I was lucky enough to spend some time with a pair of identical twin brothers who are at really different places on the autism spectrum. Their names are Sam and John Fetters. They are 19. They are very tall. Sam is 6'5". John is 6'4".
BARBER: Wow.
HAMILTON: Here's how Sam describes John, who is sitting right beside him on the couch while we talk.
SAM FETTERS: He's so smart. He knows, like - you know, like, every single episode of "Sesame Street."
JOHN FETTERS: Yeah.
S FETTERS: And "The Muppet Show."
J FETTERS: Yes.
S FETTERS: He has them all, like, stored in here in a way that is, frankly, extremely impressive to me.
HAMILTON: And here is what John says when I ask him to describe his brother.
J FETTERS: He's Sam.
HAMILTON: He is definitely Sam. And what does Sam like to do?
J FETTERS: He - using his computer.
HAMILTON: What does he do on his computer?
J FETTERS: Using his games.
BARBER: They're different for sure, but has that difference affected their lives?
HAMILTON: It has. Sam is a sophomore at Amherst College. John goes to a school for people with special needs. Sam loves to talk. He can carry on a conversation about pretty much anything. For John, autism has made language a real challenge. He also tends to repeat the words he's just heard, and he flaps his hands. Sam told me those behaviors make his brother really vulnerable when people are cruel.
S FETTERS: Someone compared me to Rain Man once. And one of the ways you avoid that is trying to, like, present much more neurotypical. And I can do that. My brother can't.
BARBER: OK. So they have the same genes but a different result. Do scientists know why?
HAMILTON: Not yet, but they've got some ideas. And the hope is that understanding the difference between identical twins like Sam and John will help show what changes in the brain result in autism.
BARBER: Today on the show, what scientists are learning from identical twins on the spectrum. I'm Regina Barber. You're listening to SHORT WAVE, the science podcast from NPR.
(SOUNDBITE OF MUSIC)
BARBER: OK. I know identical twins have exactly the same genes, but what does that mean for an autism diagnosis?
HAMILTON: Autism is this highly genetic condition that seems to involve multiple genes. It runs in families quite often. And in a given family, if one sibling is autistic, there's a much greater chance that the other siblings will be as well. Where you really see the difference, though, is in identical twins.
BARBER: Because, I mean, if something is genetic, you'd see it in both people, right?
HAMILTON: Not always is the answer there. You know, if one identical twin is on the spectrum, it is really, really likely the other twin will be as well. At least one study showed there was more than 90% what they call concordance. What's interesting is that these genetically identical siblings can have really different levels of autism - you know, like Sam and John, the twins we heard from before the break.
BARBER: Does that mean that it's not just about genes, but there's, like, other factors involved in how autism manifests?
HAMILTON: That's what scientists think. They're still trying to understand which factors, though. You know, one may be that one twin experiences an injury or an illness that somehow makes their brain react differently to the genetic factors that are involved in autism.
BARBER: Could any of those things explain why Sam and John are different, like, when it comes to autism?
HAMILTON: Maybe. I mean, there's no way to be sure. But this is something I talked about with their mom. Her name is Kim Leaird.
KIM LEAIRD: John was born with a congenital heart defect, and it turned out he needed heart surgery to close his - the hole in his heart was that big. So he got through that, and he developed a really bad staph infection in his incision scar. And he had to have a central IV and really strong antibiotics.
BARBER: That's a pretty harrowing way to start life. I mean, does their mom think that's what made John's autism so different than Sam's?
HAMILTON: Kim isn't sure, but she told me that the difference between Sam and John really wasn't that apparent when her boys were toddlers.
LEAIRD: They were very similar. They both did not wave. They didn't respond to their name. They both had a lot of repetitive, you know, movements. They would line things up and open and close doors. It was only when Sam started talking, and we were like, well, what's going on with John?
BARBER: So do scientists have any idea of how something like infection could make autism more severe?
HAMILTON: They have some hypotheses, right?
BARBER: OK.
HAMILTON: Scientists always do. There's some thinking that maybe something like that could limit the brain's ability to adapt to genetic differences, you know, that influence things like language. That's speculation, of course. But what is clear is that identical twins offer this amazing window on the interaction between the DNA that you start out with and what happens to you early in life, and how it affects brain development and where you fall on the autism spectrum.
BARBER: Yeah. I mean, what have scientists learned so far from studying twins?
HAMILTON: One thing they've learned is that the conventional wisdom about autism from 50 years ago was completely wrong.
BARBER: Wow. OK.
HAMILTON: Keep in mind, that was a time when, you know, psychoanalysis was big and a lot of disorders were attributed to your experience as a young child.
BARBER: Right.
HAMILTON: All went back to that, right?
BARBER: Yeah.
HAMILTON: I talked about that with Dr. Stephanie Morris. She's a pediatric neurologist at the Kennedy Krieger Institute in Baltimore.
STEPHANIE MORRIS: The earliest, earliest twin studies really helped to debunk this theory that autism was caused by parenting, by these - what were referred to as refrigerator mothers, right? Which is this concept that autism was a direct result of moms in particular who were cold and emotionally detached and distant from their child.
BARBER: Like, I've never actually heard of refrigerator moms, but, of course, it must be the mom's fault, right?
HAMILTON: Yeah, tempting for a lot of those researchers. But no, it's - that's not how it played out. The twin studies were really critical to showing that because they let scientists study kids at the same age who'd been raised by the same parents. And guess what? Parenting doesn't make kids autistic. But when scientists began studying identical twins, they realized that genes aren't the complete explanation either. There's got to be something else going on.
BARBER: So with Sam and John, it could have been this heart surgery or the infection or all those antibiotics. But what are the other things scientists are looking at?
HAMILTON: One thing is the condition in the womb, you know, the environment of the womb during pregnancy.
BARBER: Right. That's what I was thinking.
HAMILTON: Well, I mean, 'cause twins aren't necessarily the same. One might get more oxygen or more nutrients than the other during pregnancy. Then, either before or after birth, maybe one twin is exposed to a toxin or something, you know, while the other isn't. And Stephanie says, even though identical twins start out with identical genes, this doesn't mean all their cells turn out exactly the same way.
MORRIS: There's also this concept of other non-shared genetic factors that could be influenced. So things like epigenetics, which is the modification of our DNA that happens over time as a result of both gene-gene interaction, as well as gene-environment interaction.
HAMILTON: So as you can hear, you know, scientists are still trying to figure out how all of these factors change brain development in autism. And it's tough because when you compare the brain of an autistic person with the brain of a neurotypical person, the differences are really subtle, you know, if they're detectable at all.
BARBER: Wow.
HAMILTON: So, for example, there seems to be a slightly different growth pattern in the brain with autism, and the connections between brain areas seem to be slightly different.
BARBER: So are twins going to be the best way to find these brain differences?
HAMILTON: That's one way. I think scientists would love to know precisely how Sam's brain and John's brain are different and when that difference occurred. You know, understanding that might be really useful in figuring out how to help someone like John acquire more language. It might make it easier for him to communicate with his mom and his brother.
BARBER: I mean, how does John communicate now, like, when he can't find, like, the right words?
HAMILTON: Sometimes he points to a favorite episode of "Sesame Street." Other times, he communicates physically. When he and Sam were together - and I was with them quite a bit - John stayed really close to his brother, and he often wanted to be in physical contact. He likes to have Sam hold his hand when they go places. Here's what Sam told me about this.
S FETTERS: Touch is a way of, like, communicating too. If language isn't as much a method of communication, then all the other senses become a lot more kind of important and meaningful.
BARBER: Sam sounds like a great brother.
HAMILTON: He really is. And he is also really good at - I don't know what to say - translating from John. You know, for example, I was there when Sam kind of stepped in when I asked John to name his favorite episode of "Sesame Street."
J FETTERS: Abby makes the seasons change.
HAMILTON: Say that again.
J FETTERS: Abby Cadabby makes the seasons change.
S FETTERS: There's an episode with Abby Cadabby, Rosita and Zoe where they dance around with, like, the seasons changing, and I think that's the one he's referring to.
HAMILTON: And Sam told me that he does wish it was easier for his brother to express all the thoughts and feelings he's having. But he also said, you know, that's kind of a small thing.
S FETTERS: He still means the world to me, and I wouldn't have him any other way.
BARBER: Thanks, Jon. I'm really glad I got to know these brothers at least a little bit.
HAMILTON: Me, too, Gina.
BARBER: This episode was produced by Rachel Carlson and edited by our show runner, Rebecca Ramirez. Jon checked the facts. The audio engineers were Phil Edfors and Gilly Moon. Beth Donovan is our senior director. And Colin Campbell is our senior VP of podcasting strategy. I'm Regina Barber. Thank you for listening to SHORT WAVE from NPR.
Copyright © 2024 NPR. All rights reserved. Visit our website terms of use and permissions pages at www.npr.org for further information.
NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.