DNA methylation mediates the multiple sclerosis onset risk associated with HHV-6 DNA positivity

In Ausimmune, an Australian multicenter incident case-control study, Epstein-Barr virus (EBV)-related measures, including anti-EBNA antibodies and infectious mononucleosis, show multiple sclerosis (MS) associations mediated by DNA methylation (DNAm). Human herpesvirus-6 (HHV-6) DNA has also been linked to increased MS onset risk, though its mechanisms remain unknown. Therefore, we examined an expanded set of human herpesvirus indices including HHV-6 indices. We first tested associations with MS-associated DNAm modules, then assessed whether HHV-6 DNA contributes to MS onset through DNAm pathways. Serological (serum) and viral load (whole blood) measures of EBV (DNA, viral capsid antigen, early antigen diffuse and restricted), HHV-6 (DNA, IgM, IgG), cytomegalovirus (CMV) (IgG), and varicella zoster virus (DNA, IgG) were collected. DNAm was measured from whole blood (Illumina Infinium Human Methylation EPIC v1). DNAm-module (A1-A5) scores were derived using an epigenome-wide association study for MS onset risk and dimension-reduction methods. A total of 206 cases and 348 matched controls were analyzed. Multivariable linear regression demonstrated associations between HHV-6 DNA positivity and the A2-module, and between higher CMV IgG and the A4 module. Counterfactual mediation analysis indicated that 45% of the positive association of HHV-6 DNA positivity with MS onset risk was mediated through the A2 module (P _indirect = .008). The A2 module showed enrichment for lymphatic and immune pathways. These results provide evidence for a distinct DNAm module as a plausible mechanism underlying the associations of HHV-6 with MS onset. Importantly, these epigenetic pathways appear to mediate associations with human herpesviruses beyond EBV. These findings provide further insights into how environmental factors relate to MS onset through epigenetic programming.