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Gene mutation provides resilience to cold
寒潮来袭！为什么有人冬天穿短袖都不冷？
Skeletal muscle comprises fast-twitch muscle fibers that fatigue quickly and slow-twitch muscle fibers that are more resistant to fatigue. The protein α-actinin-3, which is found only in fast-twitch muscle fibers, is absent in almost 20 percent of people — almost 1.5 billion individuals — due to a mutation in the gene that codes for it.
人的骨骼肌由快缩肌纤维和慢缩肌纤维组成，前者易疲劳，而后者更耐疲劳。α-辅肌动蛋白-3是一种只存在于快缩肌纤维内的蛋白质。由于基因突变，全球近20%的人（约15亿人）体内完全没有这种蛋白质。
Researchers at Karolinska Institute in Sweden now show that more of the skeletal muscle of these individuals comprises slow-twitch muscle fibers, which are more durable and energy-efficient, and provide better tolerance to low temperatures than fast-twitch muscle fibers. The results are published in the American Journal of Human Genetics.
来自瑞典卡罗林斯卡学院的研究人员表示，这些人的骨骼肌更多由慢缩肌纤维构成。与快缩肌纤维相比，这一肌纤维更加持久，所需能量较少，而且对低温的耐受力更强。该研究结果发表于《美国人类遗传学杂志》。
"This suggests that people lacking α-actinin-3 are better at keeping warm and, energy-wise, at enduring a tougher climate, but there hasn't been any direct experimental evidence for this before," says H?kan Westerblad, a professor of cellular muscle physiology at the Department of Physiology and Pharmacology.
卡罗林斯卡学院生理学和药理学系的细胞肌肉生理学教授霍坎?维斯特布拉表示：“这表明缺乏α-辅肌动蛋白-3的人更擅于保暖，能够在极端天气中调节自身能量。但此前没有发现任何直接的实验证据。”
For the study, 42 healthy men between 18 and 40 were asked to sit in cold water (14 °C) until their body temperature dropped to 35.5 °C. During cold water immersion, researchers measured muscle electrical activity with electromyography (EMG) and took muscle biopsies to study the protein content and fiber-type composition.
在实验时，42名年龄在18岁至40岁之间的健康男性被要求坐在14℃的冷水中，一直持续到他们的体温下降至35.5℃。在浸入冷水的过程中，研究人员用肌电图测量受试者的肌电活动。另外他们还进行了肌肉活检以研究蛋白质含量和纤维类型组成。
The results showed that the skeletal muscle of people lacking α-actinin-3 contains a larger proportion of slow-twitch muscle fibers. On cooling, these individuals were able to maintain their body temperature in a more energy-efficient way. Rather than activating fast-twitch muscle fibers, which results in overt shivering, they increased the activation of slow-twitch muscle fibers that produce heat by increasing baseline contraction.
结果显示，这些缺乏α-辅肌动蛋白-3的人的骨骼肌中含有较大比例的慢缩肌纤维。在降温中，这些人能够通过节省能量来维持自身的体温。快缩肌纤维会靠颤抖来对抗低温，而这些人则是通过增加肌肉收缩（肌紧张），激活慢缩肌纤维来产生热量。
"The mutation probably gave an evolutionary advantage during the migration to a colder climate, but in today's modern society, this energy-saving ability might instead increase the risk of diseases of affluence, which is something we now want to turn our attention to," says Westerblad.
维斯特布拉说：“这一基因突变很可能是为了满足向寒冷地域迁徙的进化需要。但在现代社会中，这种储存能量的能力反而会增加患多种疾病的风险，这是我们目前需要关注的问题。”
Marius Brazaitis, a scientist at the Lithuanian Sports University says，"It is our hypothesis or assumption at this point that people with the gene variant who consume more calories and are physically inactive could be at a higher risk of obesity, type-2 diabetes, and other metabolic disorders."
来自立陶宛体育大学的科学家马吕斯?布雷扎伊蒂斯表示：“我们目前推测，具有这种变异基因的人会摄入更多的卡路里，同时还缺乏锻炼，这可能会增加患肥胖症、2型糖尿病及其它代谢紊乱疾病的风险。”
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