Gene mutation provides resilience to cold
基因突变带来了抗寒能力
Skeletal muscle comprises fast-twitch muscle fibers that fatigue quickly and slow-twitch muscle fibers that are more resistant to fatigue.
人体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。
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.
辅肌动蛋白α-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.
瑞典卡罗林斯卡学院的研究人员发现，这些人的骨骼肌更多是由慢缩肌纤维构成，它们比快缩肌纤维更耐用、更节能，对低温的耐受性更好。该研究结果发表在《美国人类遗传学杂志》上。
"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 Hakan 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：“这表明缺乏辅肌动蛋白α-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 Celsius degree) until their body temperature dropped to 35.5 Celsius degree.
在这项研究中，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，直到他们的体温降至35.5℃。
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.
在冷水浸泡期间，研究人员用肌电图测量肌肉电活动，并进行肌肉活组织检查，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.
结果表明，缺乏辅肌动蛋白α-3的人骨骼肌中含有较大比例的慢缩肌纤维。在降温时，这些人能够以更节能的方式保持体温。
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.
他们并没有激活快缩肌纤维，从而导致明显的颤抖，而是通过增加肌肉收缩来激活慢缩肌纤维，从而产生热量。
"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。”
“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,” Marius Brazaitis, a scientist at the Lithuanian Sports University says.
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，携带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。”
(标红单词为考研重难点词汇)
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