The present protocol seeks to advance our understanding of sclerosing glomerular and tubulointerstitial kidney diseases, including but not limited to variants of focal segmental glomerulosclerosis (FSGS) and chronic kidney disease of unknown etiology (CKDu). This protocol will encompass studies of the natural history, pathogenesis and treatment of these chronic kidney disorders. It will also allow us to: (1) provide second opinions to referring physicians about management of subjects with these relatively rare kidney diseases; (2) collect research samples (e.g., blood), urine, and kidney tissue obtained from clinically-indicated or from research renal biopsies); (3) and treat these subjects with standard or other approved therapies; or (4) invite selected subjects patients to participate in limited pilot studies of novel combinations of standard therapeutic agents, such as rituximab and cyclosporine. (5) Agricultural worker chronic kidney disease of undetermined etiology (CKDu) is a growing problem in tropical countries in the Americas and Asia, including Sri Lanka where collaborators are located. We will receive kidney tissue from 25 CKDu cases for pathologic examination and transcriptional profiling and blood, plasma, serum, urine for metabolomic and genetic analysis from 50 cases and controls. Subjects were consented and samples were collected under a protocol approved by the University of Colombo IRB. These studies may provide the opportunity to generate new hypotheses regarding pathogenesis and treatment that would be candidates for testing in other research protocols.