青春期主要特征:苗条身材原来是与生俱来的！

  Those annoying people who claim that they can eat what they like but never put on weight may have had a second helping of a newly discovered 'skinny gene'. 

While many genes have been identified as leading to obesity, this is the first time a genetic explanation for 'extreme thinness' has been unveiled. 

以前找到的很多都是能够导致人肥胖的基因，而“瘦身”基因是首例发现的可以让人变得异常苗条的遗传因子。

According to a study published in the journal Nature, the genes in question are a group of 28 that form part of chromosome 16.

Last year the same research team found that people without these genes are 43 times more likely to be morbidly obese. 

However, it has now been revealed that people in whom these particular genes are duplicated are more likely to be skinny. 

根据一项发表在《自然》杂志的研究，这类“瘦身”基因由人类第16号染色体上的28个基因构成。这个课题组在去年的研究中发现，不携带这些基因的人群患肥胖症的几率是常人的43倍；而最新的研究结果发现，如果这些基因在染色体中出现重复，人的体型会更为苗条。

It mean that fatness and thinness could be two sides of the same coin.

Researchers at Imperial College London and the University of Lausanne in Switzerland said around one in 2,000 people have the duplicated genes, making men 23 times more likely to be underweight, and women five times more likely. 

这意味着，胖与瘦只是一枚硬币的两个面，因为它们可能被同一类基因所控制。

伦敦帝国理工学院和瑞士洛桑大学的研究者声称，在每两千个人当中会有一个人带有复制的“瘦身”基因，如果这个人是男人，他偏瘦的可能性是平常人的23倍；如果是女人，偏瘦的可能性是平常人的5倍。

Normally, each person has a copy of each chromosome from each parent, giving them two copies of each gene. 

But sometimes sections of a chromosome can be duplicated or deleted, resulting in an abnormal 'dosage' of genes, the researchers explained in their study. 

人有23对染色体，每对染色体有一条来自于父亲，一条来自于母亲，所以染色体上的基因通常也都是两个拷贝。但有时候，一条染色体的某些区段会发生重复或者缺失，导致位于这些区段上面的基因数量发生改变，研究者这样解释。

'This is the first genetic cause of extreme thinness that has been identified,' said Professor Philippe Froguel from Imperial's school of public health, who led the study. 

'It's also the first example of a deletion and a duplication of one part of the genome having opposite effects.'          

“这是首次鉴定到会使人非常苗条的遗传因子，”项目负责人，帝国理工大学公共卫生系的菲利普·弗罗盖尔教授说：“基因组一段的缺失和重复对人体产生截然相反的效果，这也是一个崭新的发现。”

The discovery has important implications for diagnosis in children's health

A non-specific condition in children known as 'failure to thrive' - where their rate of weight gain is significantly lower than normal - has been diagnosed in half of all children with the genetic duplication, the study showed. 

It means 'failure to thrive' can be genetically driven. 

这一发现可能会对儿科诊断产生积极影响。某些儿童在成长过程中体重的增加速度显著低于正常儿童，这种先天性疾病被称作“生长不良”。而在这项研究中发现，半数“生长不良”的儿童携带有重复的“瘦身”基因，这说明这种疾病可能是由遗传因素所导致。

'If a child is not eating, it's not necessarily the parents' fault,' said Prof Froguel.  He added that scientists still have much work to do to find out more about the genes in this region, but their discovery could eventually lead to new potential treatments for obesity and appetite disorders.    

'If we can work out why gene duplication in this region causes thinness, it might throw up new potential treatments for obesity and appetite disorders,' he said.

'We now plan to sequence these genes and find out what they do, so we can get an idea of which ones are involved in regulating appetite.               

 

                        Froguel's team examined the DNA of more than 95,000 people for their study for which being underweight was defined as having a body mass index (BMI) below 18.5 kg per metre squared.          

The research also showed a quarter of people with the duplication had microcephaly, a condition in which the head and brain are abnormally small and which is linked to neurological defects and shorter life expectancy.

弗罗盖尔教授的研究小组检测了超过9万5千个偏瘦个体（身体质量指数BMI低于18.5 kg/m2）的DNA，结果显示具有重复“瘦身”基因的人当中，有四分之一患有小头症。其患者头部和脑的体积异常的小于平均水平，而且这种病还与神经功能缺陷和短寿有联系。

Genes are stretches of DNA that provide the coded instructions for making proteins.

They generally come in pairs and are housed in the chromosomes, the packaged bundles of DNA inherited from each parent.

However sometimes parts of either chromosome in a pair can be deleted or duplicated. 

When this happens, there can be too many copies of a certain gene or too few.

As a result, a gene might be abnormally active or not active enough.

基因是编码蛋白质的DNA序列，通常它们在染色体中成对出现，而染色体是两条凝缩的DNA链，分别来自于父亲和母亲。但有些时候，一条染色体中的某个区段可能发生丢失或者重复，这样就会导致位于这一区段上面的基因数量减少或是增加，最后的结果就是这个基因可能会异常的沉默或者活跃。

As regards the 'skinny gene', Prof Froguel said: 'The dogma is that we have two copies of each gene, but this isn't really true.

'The genome is full of holes where genes are lost, and in other places we have extra copies of genes. In many cases, duplications and deletions have no effect, but occasionally they can lead to disease.

再回到“瘦身”基因上，“理论上，每个基因都要两个拷贝，但实际上不完全是这样。”弗罗盖尔教授说，“基因组中有缺失的区段，上面基因就会缺失，而在其他位置的基因也可能存在多余的拷贝。大多情况下，基因的重复和缺失并不会造成影响，但某些情况下它们会导致疾病。”

'So far, we have discovered a large number of genetic changes that lead to obesity. 

'It seems that we have plenty of systems that increase appetite since eating is so important - you can suppress one and nothing happens. 

“迄今为止，我们找到了很多导致肥胖的遗传突变。毕竟，人是铁饭是钢看起来，所以人体内好像有很多体系可以增强食欲，某一个体系被抑制了并无影响。”

'This is the first genetic cause of extreme thinness that has been identified.'

Duplications in the same region have also been linked to schizophrenia, while deletions are associated with autism.

“这是首次鉴定到会使人非常苗条的遗传因子。”“瘦身”基因所在的染色体区段，如果发生重复还会导致精神分裂症，而缺失则会引起孤独症。