Relapsing-remitting multiple sclerosis and human herpesvirus 6 active infection

Background: Recent studies have focused on the relationship between human herpesvirus 6 (HHV-6) and multiple sclerosis (MS). Objective: To analyze HHV-6 messenger RNA expression in patients with relapsing-remitting (RR) MS vs healthy blood donors (HBDs). Design: One hundred fifty-four subjects were enrolled in the study: 105 patients with RRMS (32 in relapse) and 49 HBDs. Total DNA and messenger RNA were extracted from serum and blood samples, respectively, and analyzed by quantitative real-time reverse transcription-polymerase chain reaction for the detection of 3 HHV-6 immediate-early genes (U16/U17, U89/U90, and U94) and both HHV-6 variants (HHV-6A and HHV-6B). Results: Active HHV-6 infection was detected in 16% of patients with RRMS vs 0% of HBDs (P=.003). Seven patients with RRMS with exacerbation had HHV-6 active replication, and the virus remained latent in only 1 of them. We did not find any statistically significant difference between HHV-6 active or latent infection for patients in remission (P=.12). Among patients with RRMS with HHV-6 active replication, viral load was higher when they experienced an acute attack than when in remission (P=.04). In those patients with RRMS who had an active infection only, HHV-6A was found. Cell-free HHV-6 DNA detected in serum samples confirmed the results. Conclusions: The results show that a subset of patients with RRMS experience HHV-6 active infection, and there likely is an association between the viral active replication and relapses; therefore, HHV-6 active infection may imply a greater risk of exacerbations in a subgroup of patients with RRMS.