MOLECULAR BASIS OF HIGH DENSITY LIPOPROTEIN DEFICIENCY

冠心病（CHD）是导致人类死亡和残疾的主要原因之一。血浆高密度脂蛋白胆固醇（HDL-C）浓度低于35 mg/dl已被定义为主要的独立冠心病危险因素。HDL-C浓度的变化大约有一半是由环境因素决定的，比如饮食、酒精摄入量和运动，但也有很强的遗传成分。据报道，参与血浆HDL-C浓度调节的关键酶基因发生了许多突变，包括胆固醇酯转移蛋白（CETP）、肝脂肪酶（HL）、卵磷脂：胆固醇酰基转移酶（LCAT）和脂蛋白脂肪酶（LPL）。然而，只有LPL在普通人群中发现了常见的突变。其中两个，Asn291产生Ser和Asp9产生Asn突变，降低LPL活性，升高甘油三酯和降低HDL-C，而相反，第三个突变，Ser447X，增强LPL活性，降低甘油三酯和升高HDL-C。尽管这些突变已被证明会影响冠心病的风险，但它们在高密度脂蛋白缺乏患者中的发生频率尚未得到评估。因此，本研究项目的目的是：1)从2531名参加前瞻性退伍军人管理局HDL干预试验（HIT）的男性中分离DNA，这些人的HDL- c水平均低于40 mg/dl，并已确诊为冠心病；2)确定该人群中三种常见LPL突变的频率，并将这些数据与Framingham后代研究（FOS）中没有冠心病证据的年龄匹配男性的数据进行比较；最后3)评估这三种LPL变异与HIT受试者对gemfibrozil （n=1265）和/或口服脂肪激发（n=600）的反应之间的关系。我们假设，与FOS组相比，HIT研究组中Asn291产生Ser和Asp9产生Asn突变的频率要高得多，Ser447X突变的频率要低得多。在FOS对照中，我们发现在杂合状态下，这些LPL突变的频率分别为0.026、0.028和0.168。此外，我们假设具有前两种突变中的任何一种的HIT受试者在降低甘油三酯和升高HDL-C方面对吉非齐齐治疗的反应较差，并且在处理口腔脂肪挑战方面效率较低，而具有后一种突变的患者在这方面反应更强，效率更高。这项研究将为我们提供关于LPL突变在测定低血浆HDL-C浓度中的作用的重要信息。

Coronary heart disease (CHD) is a major cause of death and disability in our society. A plasma high density lipoprotein cholesterol (HDL-C) concentration of less than 35 mg/dl has been defined as a major independent CHD risk factor. Approximately half of the variation in HDL-C concentrations is determined by environmental factors, such as diet, alcohol intake, and exercise, but there is also a strong genetic component. A number of mutations have been reported in the genes for key enzymes involved in the regulation of plasma HDL-C concentrations, including cholesteryl ester transfer protein (CETP), hepatic lipase (HL), lecithin:cholesterol acyltransferase (LCAT), and lipoprotein lipase (LPL). However, only for LPL have common mutations been identified in the general population. Two of these, the Asn291 yields Ser and Asp9 yields Asn mutations, decrease LPL activity, raising triglycerides and lowering HDL-C, while, conversely, the third mutation, Ser447X, enhances LPL activity, reducing triglycerides and elevating HDL-C. Although these mutations have been shown to affect CHD risk, their frequency in patients with HDL deficiency has not yet been assessed. Hence, the purpose of this research project is to: 1) isolate DNA from 2531 men participating in the prospective Veterans Administration HDL Intervention Trial (HIT), all of whom have an HDL-C level of less than 40 mg/dl and established CHD, 2) determine the frequencies of the three common LPL mutations in this population and compare these data with those of age-matched men in the Framingham Offspring Study (FOS) having no evidence of CHD, and, lastly 3) assess the relationships between these three LPL variants and response to gemfibrozil (n=1265) and/or an oral fat challenge (n=600) in HIT subjects. We hypothesize that there will be significantly higher frequencies of the Asn291 yields Ser and Asp9 yields Asn mutations and a significantly lower frequency of the Ser447X mutation in the HIT study group relative to the FOS group. In FOS controls, we have shown the frequencies of these LPL mutations to be 0.026, 0.028, and 0.168, respectively, in the heterozygous state. Moreover, we hypothesize that those HIT subjects with either of the former two mutations will be less responsive to gemfibrozil therapy in terms of triglyceride lowering and HDL-C raising, as well as less efficient at handling an oral fat challenge, whereas those with the latter mutation will be more responsive and more efficient in this regard. This research will provide us with important information about the role of LPL mutations in the determination of low plasma HDL-C concentrations.