1. Pediatric Nephrology Unit, Hospital Exequiel Gonzalez Cortes, Ramón Barros Luco 3301, Santiago, Chile
2. Faculty of Medicine, University of Chile, Av. Independencia 1027, Santiago, Chile
3. Faculty of Medicine, Catholic University, Av Libertador Bernardo O Higgins 340, Santiago, Chile
4. Institute of Maternal and Child Research, Faculty of Medicine, University of Chile, Casilla 226-3, Santiago, Chile