Gut microbes can influence numerous aspects of human biology. Alterations in the function and composition of gut microbial flora (gut microbiota ) have been linked to inflammatory bowel disease, chronic inflammation, dyslipidemia, diabetes mellitus, atopic disorders, cardiovascular disease, neoplasms, and obesity. However, little is known whether renal failure alters the composition of gut microbiota and whether an alteration in the gut microbiota of patients with renal failure impacts on the development of co-morbid conditions such as accelerated atherosclerosis, abnormal bone mineral metabolism, and chronic inflammation that are associated with renal failure. Nonetheless, several lines of evidence suggest that renal failure alters the chemical environment of the intestinal lumen, which could impose a selective pressure on the growth of certain gut microbes. The investigators hypothesize that the gut microbiota of patients with renal failure is different from those without renal failure. To test this hypothesis the investigators are conducting a cross-sectional study of gut microbiota in patients with different degrees of renal failure due to polycystic kidney disease (PKD).