Identification of endogenous normalizers for serum MicroRNAs by microarray profiling: U6 small nuclear RNA is not a reliable normalizer

We read with great interest the article entitled ‘‘Ethnic Differences in Viral Dominance Patterns in Patients with Hepatitis B Virus and Hepatitis C Virus Dual Infection,’’ recently published by Nguyen et al. in this journal. The study was designed to evaluate and compare the demographic, clinical, and viral characteristics of multiethnic patients infected by hepatitis virus admitted at two large liver centers in the United States. The investigators defined the study design as a matched case-control study, in which the case group included patients with hepatitis B virus (HBV) and hepatitis C virus (HCV) dual infection, and the control group comprised patients with HBV monoinfection. However, in our opinion, there is an important methodological issue in the reported data: The main conclusion of the article was not about the comparison between cases and controls, but rather it underscored a secondary analysis with cases only in which ethnic differences were examined in terms of viral dominance patterns among HBV and HCV dual-infected patients. It is our opinion that the investigators deviated from the scope of the case-control study originally proposed, because it is clear that the investigation was not delineated to test the hypothesis that ended up becoming the core conclusion, including the title of the article. Therefore, the investigators’ conclusions regarding viral dominance were not consistent with the a priori study aims proposed.