GENETIC MAPPING IN THE HYPERCALCIURIC STONE-FORMING RAT

特发性高钙尿症（IH）是人类最常见的与肾结石相关的代谢异常，多达45%的IH患者有肾结石家族史。高钙尿酸肾结石患者的定义亚群包括常染色体或X连锁遗传的患者，但总体而言，人类IH的表型是一种复杂的多基因疾病。由于需要大量的家族、饮食变量和IH患者所描述的大量代谢亚群，对人类高钙尿的遗传学进行全面调查将变得困难。然而，在遗传高钙尿酸结石形成（GHS）大鼠中存在动物模型，该大鼠目前已进入第51代近交。在这个模型中，高钙尿的生理学已经被广泛表征，并且在许多重要方面与人类IH相似。David Bushinsky博士通过选择性地培育每一代高钙血症最多的窝鼠，建立了GHS大鼠群体，并且可能富含导致高钙血症的基因等位基因。现在有了一套强大的工具来对大鼠进行遗传和物理定位，而且还在迅速扩大。该项目的目标是绘制决定GHS大鼠高钙尿症的基因图谱。本项目的第一个目的是通过QTL定位鉴定与高钙尿相关的数量性状位点（QTL）。该分析将利用简单序列长度多态性（SSLPs）对GHS和正常钙量Wistar-Kyoto （WKY）大鼠之间的F2杂交进行选择性基因分型。二是通过构建和分析大鼠同源菌株，进一步完善QTL定位。我们在156只大鼠的初始F2全基因组扫描方面取得了实质性进展，并在1号染色体上发现了一个符合显著性保守标准（LOD 4.5）的QTL和两个符合“暗示”连锁标准的位点。更精确的定位最终将使高钙尿症基因的物理定位和位置克隆成为可能，这将允许未来研究这些基因的同源物，以确定它们在人类特发性高钙尿症中的作用。

Idiopathic hypercalciuria (IH) is the most common metabolic abnormality associated with kidney stones in humans, and as many as 45 percent of patients with IH have a family history of nephrolithiasis. Defined subsets of patients with hypercalciuric nephrolithiasis include those with autosomal or X linked inheritance, but overall the phenotype of human IH is that of a complex, polygenic disease. A full-scale investigation of the genetics of human hypercalciuria would be made difficult by the large number of families required, dietary variables, and number of metabolic subsets described in patients with IH. However, an animal model exists in the genetic hypercalciuric stone-forming (GHS) rat, which is now in its 51st generation of inbreeding. The physiology of hypercalciuria in this model has been extensively characterized and resembles human IH in many important respects. The GHS rat colony was established by Dr. David Bushinsky by selectively breeding the most hypercalciuric littermates of each generation, and is likely to be enriched in alleles for genes that contribute to hypercalciuria. A robust armamentarium of tools for genetic and physical mapping in rats is now available, and expanding rapidly. The goal of this project is to map genes determining hypercalciuria in the GHS rat. The first aim of this project is to identify quantitative trait loci (QTL) linked to hypercalciuria through QTL mapping. This analysis will make use of selective genotyping of an F2 intercross between GHS and normocalciuric Wistar-Kyoto (WKY) rats, using simple sequence-length polymorphisms (SSLPs). The second aim is to refine the QTL localization further by constructing and analyzing congenic strains of rats. We have made substantial progress towards a whole-genome scan in an initial F2 of 156 rats, and have identified one QTL on chromosome 1 that meets conservative criteria for significance (LOD 4.5) and two loci that meet criteria "suggestive" of linkage. More precise localization should eventually make possible physical mapping and positional cloning of genes contributing strongly to hypercalciuria, which will allow for future work in which homologues of these genes can be studied to determine their role in human idiopathic hypercalciuria.