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，高达45%的IH患者有肾结石家族史。定义的高钙尿性肾结石患者亚群包括那些具有常染色体或X连锁遗传的患者，但总的来说，人类IH的表型是一种复杂的多基因疾病。由于IH患者所需的大量家系、饮食变量和代谢亚群的数量，全面调查人类高钙尿症的遗传学将变得困难。然而，遗传性高钙尿性结石形成(GHS)大鼠存在一个动物模型，它现在处于第51代近亲交配。在这个模型中，高钙尿症的生理学已经被广泛地描述，并在许多重要方面与人类IH相似。GHS大鼠群体是由David Bushinsky博士通过有选择地培育每一代中高钙尿量最多的小鼠而建立的，很可能富含导致高钙尿症的基因的等位基因。一种强大的工具，用于在老鼠身上绘制遗传和物理图谱，现在已经可以使用，而且正在迅速扩大。该项目的目标是定位决定GHS大鼠高钙尿症的基因。本项目的第一个目标是通过QTL定位来确定与高钙尿相关的数量性状基因座(QTL)。这项分析将利用简单序列长度多态(SSLP)对GHS和正常钙尿Wistar-京都(WKY)大鼠之间的F2杂交进行选择性基因分型。第二个目的是通过构建和分析大鼠的同源品系，进一步完善QTL定位。我们在对156只大鼠的初始F2进行全基因组扫描方面取得了实质性进展，并在1号染色体上鉴定出一个符合保守意义标准(LOD 4.5)的QTL和两个符合连锁标准的基因座。更精确的定位最终将使物理定位和位置克隆成为可能，这将为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奠定基础。

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.