Fetal inheritance of chromosomally integrated human herpesvirus 6 predisposes the mother to pre-eclampsia.

Pre-eclampsia (typically characterized by new-onset hypertension and proteinuria in the second half of pregnancy) represents a major determinant of the global burden of disease ^1,2 . Its pathophysiology involves placental dysfunction, but the mechanism is unclear. Viral infection can cause organ dysfunction, but its role in placentally related disorders of human pregnancy is unknown ³ . We addressed this using RNA sequencing metagenomics ^4-6 of placental samples from normal and complicated pregnancies. Here, we show that human herpesvirus 6 (HHV-6, A or B) RNA was detected in 6.1% of cases of pre-eclampsia and 2.2% of other pregnancies. Fetal genotyping demonstrated that 70% of samples with HHV-6 RNA in the placenta exhibited inherited, chromosomally integrated HHV-6 (iciHHV-6). We genotyped 467 pre-eclampsia cases and 3,854 controls and found an excess of iciHHV-6 in the cases (odds ratio of 2.8, 95% confidence intervals of 1.4-5.6, P = 0.008). We validated this finding by comparing iciHHV-6 in a further 740 cases with controls from large-scale population studies (odds ratio of 2.5, 95% confidence intervals of 1.4-4.4, P = 0.0013). We conclude that iciHHV-6 results in the transcription of viral RNA in the human placenta and predisposes the mother to pre-eclampsia.