Department of Medical Biochemistry and Immunology, Wales College of Medicine, Cardiff University, Cardiff, CF14 XN, UK.
Sci Prog. 2009;92(Pt 3-4):241-87. doi: 10.3184/003685009X12547510332240.
A staggering 4000 million people cannot digest lactose, the sugar in milk, properly. All mammals, apart from white Northern Europeans and few tribes in Africa and Asia, lose most of their lactase, the enzyme that cleaves lactose into galactose and glucose, after weaning. Lactose intolerance causes gut and a range of systemic symptoms, though the threshold to lactose varies considerably between ethnic groups and individuals within a group. The molecular basis of inherited hypolactasia has yet to be identified, though two polymorphisms in the introns of a helicase upstream from the lactase gene correlate closely with hypolactasia, and thus lactose intolerance. The symptoms of lactose intolerance are caused by gases and toxins produced by anaerobic bacteria in the large intestine. Bacterial toxins may play a key role in several other diseases, such as diabetes, rheumatoid arthritis, multiple sclerosis and some cancers. The problem of lactose intolerance has been exacerbated because of the addition of products containing lactose to various foods and drinks without being on the label. Lactose intolerance fits exactly the illness that Charles Darwin suffered from for over 40 years, and yet was never diagnosed. Darwin missed something else--the key to our own evolution--the Rubicon some 300 million years ago that produced lactose and lactase in sufficient amounts to be susceptible to natural selection.
令人震惊的是，全球有 4 亿人无法正常消化乳糖，即牛奶中的糖分。除了北欧白种人和非洲、亚洲的少数部落外，所有哺乳动物在断奶后都会失去大部分乳糖酶，而乳糖酶正是将乳糖分解为半乳糖和葡萄糖的酶。乳糖不耐受会导致肠道和一系列全身性症状，但不同种族和同一群体内的个体对乳糖的耐受程度差异很大。遗传性低乳糖酶血症的分子基础尚未确定，尽管乳糖酶基因上游解旋酶内含子中的两个多态性与低乳糖酶血症密切相关，因此也与乳糖不耐受相关。乳糖不耐受的症状是由大肠内的厌氧菌产生的气体和毒素引起的。细菌毒素可能在其他几种疾病中发挥关键作用，如糖尿病、类风湿性关节炎、多发性硬化症和某些癌症。由于各种食物和饮料中添加了含有乳糖的产品，而标签上并未注明，因此乳糖不耐受的问题更加严重。乳糖不耐受完全符合查尔斯·达尔文（Charles Darwin）四十多年来所患的疾病，但从未被诊断出来。达尔文还错过了另一件事——我们自身进化的关键——大约 3 亿年前的卢比孔河（Rubicon），它产生了足够多的乳糖和乳糖酶，从而容易受到自然选择的影响。
