Hemochromatosis modifier genes

摘要： 单一突变(HFE C282Y)的纯合是导致绝大多数病例的原因 血色素沉着症，但在纯合子中的表型表达差异很大。待检验的假说 这种修正的竞争更新是修饰基因负责表型变异。至 为了识别修饰基因，我们提出了三个具体目标。 具体目标1：确定染色体上影响铁吸收的候选修饰基因。铁代谢 在近亲交配的小鼠中以特定品系特有的方式变化。A/J品系是一种“高铁”小鼠，能吸收更多的铁 与“低铁”C57BL/6J小鼠相比，其肝脏铁含量更高。在之前的资助期间 期间，我们对代表21条小鼠染色体的21条染色体替代菌株(CS)进行了表型鉴定 A/J的遗传背景为C57BL/6J。我们使用重组Cgene菌株(RCS)来 在5号染色体的远端定位修饰区域。候选基因的分层将基于 A/J、C57BL/6J与特定重组同源株组织特异性表达差异的研究 具体目标2：描述吸收肠细胞对铁的吸收、运输和输出的调节。 初步结果表明，在没有红细胞生成剂、铁储存或海普西丁介导的信号的情况下， 小鼠吸收的铁量是由肠道细胞固有的机制调节的。我们将确定基因 在对饮食中铁含量改变的反应过程中，在肠道细胞中差异表达的基因。这些 受调控的基因将成为候选修饰基因。使用这一策略，我们已经确定了至少两个 候选修饰基因，转铁蛋白受体2，氯转运蛋白家族成员。 具体目标3：鉴定影响HFE-/-小鼠铁表型的候选修饰基因 血色素沉着症患者的同源人类基因。老鼠体内的候选修饰基因将是 对基因产物进行测序、克隆、体外表达和产生抗体。西方分析 将用于确认在特定目标1和2中检测到的基因表达差异。候选基因 序列将在其他高铁和低铁菌株中确定。一个独特的人类集合 血色病家系将用于比较同源候选修饰物的序列 同胞配对的基因具有一致和不一致的临床表型。应该找到共同的等位基因 在和谐的兄弟姐妹之间，而不是在不和谐的兄弟姐妹之间。候选基因的功能将被用来测试 铁转运和铁稳态的细胞培养模型。对修饰基因的识别可以提供 血色素沉着症风险评估方法及可能的治疗策略。

Abstract: Homozygosity for a single mutation (HFE C282Y) is responsible for the vast majority of cases of hemochromatosis, yet phenotypic expression in homozygotes varies widely. The hypothesis to be tested in this amended competing renewal is that modifier genes are responsible for the phenotypic variability. To identify modifier genes, we propose three specific aims. Specific Aim 1: Identify candidate modifier genes on chromosomes affecting iron absorption. Iron metabolism in inbred mice varies in a strain-specific manner. The A/J strain is a "high iron" mouse and absorbs more iron and has higher liver iron content compared to the "low iron" C57BL/6J mouse. During the previous funding period, we phenotyped 21 chromosome substitution strains (CSS) that represent the 21 mouse chromosomes of A/J on an otherwise C57BL/6J genetic background. We used Recombinant Cogenic Strains (RCS) to localize a modifier region on the distal end of chromosome 5. Stratification of candidate genes will be based on tissue-specific expression differences between A/J, C57BL/6J and specific recombinant congenic strains. Specific Aim 2: Characterize the regulation of iron uptake, transport and export by the absorptive enterocyte. Preliminary results indicate that in the absence of an erythropoietic, iron stores, or hepcidin-mediated signal, the amount of iron mice absorb is regulated by a mechanism intrinsic to the enterocyte. We will identify genes that are differentially expressed in enterocytes during the response to altered dietary iron content. These regulated genes will become candidate modifier genes. Using this strategy we have identified at least two candidate modifier genes, transferrin receptor 2 and a member of the chloride transporter family. Specific Aim 3: Characterize candidate modifier genes that affect the iron phenotype in Hfe -/- mice and the homologous human genes in patients with hemochromatosis. Candidate modifier genes in the mouse will be sequenced, cloned, expressed in vitro and antibodies generated against the gene products. Western analysis will be used to confirm gene expression differences detected in Specific Aims 1 and 2. Candidate gene sequences will be determined in other high iron and low iron strains. A unique collection of human hemochromatosis pedigrees will be utilized to compare the sequences of homologous candidate modifier genes in sib pairs with concordant and discordant clinical phenotypes. Common alleles should be found among concordant sibs and not among discordant sibs. The function of candidate genes will be tested using cell culture models of iron transport and iron homeostasis. Identification of modifier genes may provide a method for risk assessment for hemochromatosis and possible therapeutic strategies.