你的DNA能告诉你什么

像23andMe这样的公司提供的服务是否弊大于利?最近，分析健康风险的基因测试受到了抨击。2013年11月，基因筛查成为一个热门话题，当时FDA致信23andme公司，称该机构“担心结果不准确对公共健康造成的后果”。FDA表示，23andMe的产品构成医疗器械，必须得到该机构的批准。自从发出警告以来，23andMe已经停止销售这种筛查测试。去年12月，《纽约时报》发表了一篇题为《我拍了我的DNA照片，结果各不相同》的文章，揭示了基因筛查测试潜在的准确性问题。提交人发现，她将DNA样本寄给的三家公司对她各种疾病的健康风险有所不同。这些测试筛查了肥胖、类风湿性关节炎、乳腺癌和阿尔茨海默病等疾病。不幸的是，由于23andMe这样的公司令人不安，关于筛查的信息变得混乱，更普遍地用于各种基因筛查。并不是所有的基因筛查都是一样的，也不是所有的基因筛查都充满了《纽约时报》作者所经历的准确性问题。 Genetic screening for breast cancer involves looking at two specific genes; BRCA1 and BRCA2. The screening looks for genetic abnormalities in those particular genes, and the results of the test can yield a positive result, a negative result, or an ambiguous or uncertain result. Many women with a familial history of breast cancer choose to screen for these mutations, and research indicates that the presence of these mutations significantly increases a woman’s risk for breast cancer1. In this case, researchers know the specific genes they need to look at closely, and so this makes genetic screening for breast cancer very different from the genetic screening done for overall disease markers. For pregnant women, prenatal screenings have become an important and routine part of prenatal care.

自20世纪70年代以来，产前检测技术有了很大的进步。产前检查已经开发出800多种遗传疾病。羊膜穿刺术的新技术逐步提高了产前诊断的安全性和准确性。羊膜穿刺术利用羊水样本检测染色体异常、神经管缺陷和遗传疾病，准确度高(98-99%)2。唐氏综合症，或21号三体，是最常见的染色体异常。

遗传性疾病包括囊性纤维化等疾病。最常见的神经管缺陷是脊柱裂。这种手术是侵入性的，确实有一些风险，但对于有遗传问题或有任何这些遗传疾病的家族史的女性来说，这通常是一个推荐的行动方案。亨廷顿氏症(HD)是一种遗传性神经系统疾病，会导致不自主运动、严重的情绪障碍和认知能力下降。一个异常基因会产生HD, 1993年科学家在4号染色体上分离出了这个基因。在基因的一端，一种由三个DNA碱基(CAG)或核苷酸组成的模式在所有情况下都会重复。使用血液样本，基因测试通过计算亨廷顿基因中CAG重复的数量来分析HD突变的DNA。在正常人中，这种三核苷酸或三联体重复出现11到29次。在患有亨廷顿舞蹈症的人身上，这种重复不断地发生，从40次到80多次。这种基因筛查的结果要么是阳性的，要么是阴性的，而且准确率接近100%——如果结果是阳性的，如果你还没有出现HD症状，那么你在以后的生活中就会开始出现HD症状。 A positive result early in life enables individuals to make decisions about careers, marriage and families. While the tests 23andMe and other companies like them offer an overall snapshot of your future disease risk, much of what those screenings look for in the genetic code is not well known yet. The 23andMe test looks at only small segments of the DNA, called SNPs, and the test is limited to looking at less than a million SNPs (whereas the human genome has around 10 billion SNPs identified so far). To have your entire genome decoded would cost around $3,000 with current technology. The 23andMe test is different from looking at a specific gene, like BRCA1 or the gene that causes HD. It is important to know the differences between various types of genetic screenings, and understand the implications of the results.