1. From the Renal Division and Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA (J.P.F., G.C.C.), and Department of Internal Medicine, Division of Nephrology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands (L.S., P.E.d.J., S.J.L.B., R.T.G.).