ACTN3: why some people shiver better
Biologists have recently discovered why some people don’t gasp and shiver in the cold as much as others: a small genetic change in a gene called ACTN3 means they’re missing a crucial protein, which in turn makes their muscles better adapted for frosty weather. And this change is much more common in people who live in colder parts of the world - suggesting it evolved to help us deal with the climate. Phil Sansom spoke to Victoria Wyckelsma, a researcher at Finland’s Karolinska Institute...
Victoria - There's about 20% of people who lack this protein which is called alpha-actinin-3. And when we put these guys, about 40 men, in cold water, they had this amazing ability to maintain their temperature at a certain level.
Phil - Is that - about a fifth of people are extra-special-good at handling the cold?
Victoria - Yeah, it seems like it. So the guys who have this mutation - 70% of them could actually finish the cold challenge, so they could last the whole two hours no problem in the cold. And only about 30% of the guys with the protein could last.
Phil - I mean, I want to ask you about the biology, but first why on earth did these 40 people agree to sit in a really cold bath or something for an hour?
Victoria - It's a very good question. I think now actually it's quite topical, and it's quite popular to go swimming in such cold water. I mean, I know in Scandinavia, it's quite a new trend; I have an Australian friend who's moved to Sweden and she loves it, she's always in icy cold water. I guess they wanted to test themselves! And they weren't in for 3 hours or 2 hours straight; what we did was we put them in for 20 minutes, and then they're allowed out for 10 minutes. Then we put them back in, then we took them out. So they repeated that.
Phil - How did you connect this ability with a gene and a protein?
Victoria - It's been known for a while that there's this mutation that happens when people lack this gene. And one of the hypotheses was maybe these people have a higher tolerance to cold because they're more found in colder climates, and so we wanted to test this. And so all we had to do was take a blood sample and then we sent it to a lab. And then from that, they were able to tell us if this person was deficient in the gene, or they did have the gene.
Phil - Is the gene called alpha-actinin-3, just like the protein?
Victoria - Good question, we call it the ACTN3. So yeah, I mean, basically, yeah.
Phil - Okay, so what's going on?
Victoria - What's going on is the actinin-3 protein is actually a structural protein, and it sits within your muscle fibres; it's highly expressed in your fast muscle fibres. So you have fast muscle fibres, which help you in like athletic events such as sprinting; and then you have slow muscle fibres, which are good for endurance, so marathon running and things like that.
Phil - And where are my fast muscle fibres and where my slow ones, if I look at my body?
Victoria - They're in all your muscles.
Phil - Oh, okay.
Victoria - Your muscles are made up of a mix, and depending on which muscle group... so in the thigh muscle, you're meant to have about a 50:50 mix. So if you don't have alpha-actinin-3, your muscle acts more like a slow muscle, so you may have more of these slow fibres and they're bigger; whereas your fast fibres are actually smaller.
Phil - So alpha-actinin-3 makes the fast stuff, and when you lose it, it's less fast. Your muscles have more slow twitch; they're more of the slow type.
Victoria - Well, your muscle is far slower, we would say.
Phil - How does that help me stand the cold though?
Victoria - What happens is when you're put in a cold environment, your muscles will generate body heat for you. And one way they can do that is by shivering, and shivering is quite common in a fast muscle fibre type, but this also takes a lot of energy and it's quite exhausting, and your muscles fatigue much more quickly. And we actually associated that with the population who do have this protein. Whereas the population who are lacking this protein, they undergo more of like a low level muscle contraction to be able to generate body heat.
Phil - That seems so counterintuitive - that the standard type of shivering that you get with your fast twitch fibres is actually hindering these people in the cold.
Victoria - Yeah, absolutely. I mean, that was our main conclusion, that how we thought this was influencing these guys' ability just to stay in the cold bath for longer.
Phil - So has this been something that's really useful for people across the world that have gone up into the north, into the nouth, into colder parts of the land?
Victoria - Yeah, so they think the prevalence of this gene is far higher in areas where it's a cold climate. And they think it's more of a survival mechanism back in days before we had really nice warm apartments, and we had a large amount of food always available. The guys who were more likely to survive didn't need to make as much energy to survive and to keep themselves warm.
Phil - But then if I lived somewhere hot, is it helpful to me to have alpha-actinin-3?
Victoria - We don't know, actually. And that's probably one of the next things that we'll look towards is - what the advantages? Because apart from being a really good sprinter, we don't actually know what the positive benefits are from this.
Phil - Is there any way for me to tell if I have alpha-actinin-3?
Victoria - You could come to our lab in Sweden, have a muscle biopsy, and I could look at it for you. Or I think it's quite easy if you wanted to have a blood sample...
Phil - But there's no way you could tell from me just being... okay, so I've never been a good sprinter. I'm also not a great long distance runner! Is there any way that you could tell from what I'm like as a person? Or are there too many other factors?
Victoria - No, there's too many other other factors I think.
Phil - Okay!
Victoria - I actually have no idea because I am a terrible sprinter but I hate the cold. I don't know if that is because I am Australian and that contributes!