1. Doctorate Program in Medical Research, Research Department, Escuela Superior de Medicina, Instituto Politécnico Nacional, Mexico City 07320, Mexico
2. Masters in Health Sciences, Postgraduate Studies and Research Section, Escuela Superior de Medicina, Instituto Politécnico Nacional, Mexico City 07320, Mexico
3. Departament of Gastroenterology, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City 14080, Mexico