Genetic determinants of urine lithogenicity

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DESCRIPTION (provided by applicant): Nephrolithiasis (NL) affects up to 10% of the population producing significant pain and suffering, as well as great economic costs (up to $5.3 billion per year in the United States). Treatment strategies are imperfect and have not improved substantially over the last 30 years, in part because the key pathogenic steps remain poorly defined. Therefore, we have assembled a multidisciplinary team to define genetic risk factors for NL. A key and unique resource of our application is the Rochester, MN cohort of the Genetic Epidemiology Network of Arteriopathy (GENOA), which has conducted genome-wide linkage and association studies to identify genes influencing blood pressure and end-organ complications of hypertension (HTN). Members of the well-characterized GENOA cohort will be phenotyped for kidney stone risk via 24-hour urine measurements of lithogenic factors including calcium, oxalate, citrate, and uric acid excretion, as well as overall crystallization inhibition (upper limit of metastability, ULM). Extensive pre-existing genotyping data of the GENOA cohort will be analyzed via genome-wide linkage, together with selected NL candidate gene associations (vitamin D receptor, soluble adenylate cyclase, intracellular protease with no lysine WNK4, chloride channel CLCN5, calcium sensing receptor, urinary prothrombin fragment 1, urate anion transporter 1, oxalate-formate exchanger Slc26a6, Tamm-Horsfall Protein, osteopontin, and bikunin). These studies will determine if specific loci or candidate genes associate with corresponding urinary lithogenic factors (e.g., 24-hr excretion of calcium, oxalate, citrate, or uric acid; ULM). Genetic linkage and association analyses will control for diet and other environmental factors, and assess potential gene-environment and gene-gene interactions. These will be the first studies to assess genetic determinants of urinary lithogenic factors other than calcium in a population-based cohort, taking into account the important covariate of diet. Specific Aims are: Aim #1: Use variance component methods for univariate and multivariate quantitative trait linkage analyses to determine if urinary lithogenic measures (24-hr excretion of calcium, oxalate, citrate, and uric acid; crystallization inhibition) map to specific genomic regions in the GENOA cohort, controlling for dietary factors; Aim #2: Use family-based association methods to determine if urinary lithogenic measures (24-hr excretion of calcium, oxalate, citrate, and uric acid; crystallization inhibition) associate with polymorphisms in selected candidate genes in the GENOA cohort, adjusting for dietary factors, and determine if gene-environment and gene-gene interactions are present. Our goal is to establish genetic associations with urinary NL risk factors in a community- based cohort. The vast experience and infrastructure of GENOA investigators and use of pre-existing genotyping data will allow completion of these studies at a fraction of the cost otherwise required. Results should provide new insight into the pathogenesis of NL, and may lead to identification of new potential treatment targets.Kidney stones are common, and it is known that specific changes in the urinary composition are important risk factors, for example higher than normal calcium excretion. However, the genetic factors that cause these urinary changes have not been well defined. Therefore, in this grant we determine if specific genetic loci or candidate genes associate with kidney stone risk factors in a well-studied population for whom vast amounts of genetic data are already available, the Olmsted County GENOA cohort.