The broad interest of our laboratory are genetic causes of renal diseases. We investigate the function of disease-causing genes using genetically modified mouse models. Our ultimate goal is to identify molecular mechanisms driving renal dysfunction in pediatric patients. Our work so far has provided important insights into the role of claudin-16 in renal divalent cation homeostasis and how mutations in CLDN16 cause FHHNC (Familial Hypomagnesemia, Hypercalciuria and Nephrocalcinosis). In the course of the analysis of the mouse model, we identified a renal gene involved in magnesium homeostasis and subsequently could show that mutations in this gene (CNNM2) cause familial Hypomagnesemia. We elucidated the role of claudin-10 (CLDN10) in the sodium absorption in the thick ascending limb, which led to a discovery of CLDN10 as the genetic cause of the HELIX syndrome. Currently, we are investigating how mutations in claudins trigger the development of nephrocalcinosis and affect concentration ability of kidney and the role of CNNM2 in renal magnesium homeostasis and in brain development.