Prevalence of the -308 and -238 Tumor Necrosis Factor Alpha (TNF-α) Promoter Polymorphisms in Mexican Chronic Hepatitis C Patients Trujillo-Murillo, Pérez-Ibave, Muñoz-Mejía, Cordero-Pérez, Muñoz-Espinosa, Martínez-Rodríguez, Bosques-Padilla, Rivas-Estilla