Molecular Basis of Autosomal Dominant Hypercholesterolemia in a Multiethnic Cohor

项目简介：常染色体显性遗传性高胆固醇血症(ADH)是一种从出生起就存在的主要遗传性疾病，会导致血浆低密度脂蛋白胆固醇(LDL-C)显著升高和早发冠心病(CHD)。尽管降低低密度脂蛋白在预防冠心病方面有明显的好处，但只有不到10%的ADH患者被诊断出来，只有5%的ADH患者得到了适当的治疗。ADH在遗传上是异质性的，至少与三个基因的变异有关，包括低密度脂蛋白受体(LDLR)、载脂蛋白B-100(APOB)和前蛋白转换酶枯草杆菌素样kexin 9(PCSK9)。几个国家已经通过全国性的筛查计划和脂肪诊所网络进行了系统的筛查，以确定这些基因突变的ADH患者。这些研究发现，在临床表型为ADH的患者中，大约5%-53%的患者在这三个已知基因座中的任何一个都没有突变。大多数这些研究是在来自欧洲或日本的种族和种族相同的人群中进行的。因此，关于ADH在多种族人群中的分子基础的数据很少，特别是非裔美国人。我们在93名无关ADH患者的多种族队列中的初步数据显示，LDLR、APOB和PCSK9(“原因不明的ADH”)患者中没有任何变异的患者比例高得惊人(66%)。有趣的是，非裔美国人患“不明原因的ADH”的频率(77%)远远高于非西班牙裔白人(57%)或拉美裔美国人(53%)。因此，我们推测，新基因的突变可能是多民族人群中ADH的很大比例的基础，特别是非洲裔。该项目的总体目标是在ADH病因不明的患者中确定导致高胆固醇血症的新的基因缺陷。为了达到这个目标，我们建议对400名ADH患者进行研究。患者将从专门的血脂诊所确定，并招募他们的整个家庭。将使用标准测序技术对LDLR、APOB和PCSK9的外显子和共同剪接点的突变进行DNA筛查，或通过使用这些基因座上的信息标记进行连锁分析。LDLR外显子的缺失和复制将通过多重连接依赖的探针扩增技术进行检测。根据初步数据，我们预计将建立240名病因不明的ADH患者的队列。为了在这群“不明原因的ADH”患者中快速识别新的ADH基因，我们将利用一种结合下一代测序和位置克隆的混合方法。对脂代谢有重要影响的新基因的阐明将有助于阐明导致高血浆低密度脂蛋白-C水平和过早冠心病发生的分子过程。该项目中概述的研究将为开发预防这种潜在威胁生命的慢性疾病的新的治疗方案提供基础。

PROJECT DESCRIPTION: Autosomal dominant hypercholesterolemia (ADH) is a dominantly inherited disorder present from birth that causes marked elevation in plasma low-density lipoprotein cholesterol (LDL-C) and premature coronary heart disease (CHD). Despite the clear benefit of LDL-C lowering with regards to CHD prevention, less than 10% of cases with ADH have been diagnosed, and only 5% of ADH patients are adequately treated. ADH is genetically heterogeneous and has been associated with variants in at least three genes including LDL receptor (LDLR), apolipoprotein B-100 (APOB), and proprotein convertase subtilisin-like kexin type 9 (PCSK9). Systematic screenings to identify ADH patients with mutations in these genes has been undertaken in several countries through nationwide screening programs and lipid clinic networks. These studies have found that approximately 5%-53% of patients with a clinical phenotype of ADH do not have mutations in any of the three known loci. Most of these studies were performed in ethnically and racially homogenous populations from Europe or Japan. Thus, there is paucity of data about the molecular basis of ADH in multi-ethnic cohorts, especially African Americans. Our preliminary data in a multi-ethnic cohort of 93 unrelated ADH patients revealed a strikingly high percentage (66%) of patients without any variants in LDLR, APOB and PCSK9 ("unexplained ADH"). Interestingly, the frequency of "unexplained ADH" was much higher among African Americans (77%) than among non-Hispanic whites (57%) or Hispanics (53%). Therefore, we hypothesize that mutations in novel genes may underlie a large proportion of ADH in multi-ethnic cohorts, especially of African descent. The overall aim of this project is identify new genetic defects responsible for hypercholesterolemia in patients who have an undetermined etiology of ADH. To address this aim, we propose to study 400 patients with ADH. Patients will be ascertained from specialty lipid clinics, and their entire families will be recruited. DNA will be screened with standard sequencing techniques for mutations in the exons and consensus splice sites of LDLR, APOB and PCSK9 or by linkage analysis using informative markers at these loci. Deletions and duplications of LDLR exons will be detected with multiplex ligation-dependent probe amplification technique. Based on preliminary data, we expect to establish a cohort of 240 patients with ADH of unknown etiology. To rapidly identify new ADH genes in this cohort of "unexplained ADH" patients, we will utilize a hybrid method that combines next generation sequencing with positional cloning. Elucidation of new genes with major effects on lipid metabolism will shed light on the molecular processes that lead to development of high plasma levels of LDL-C and premature CHD. The studies outlined in this project will provide the basis for the development of new therapeutic options for the prevention of this potentially life-threatening chronic disease.