JC virus antibodies in Portuguese multiple sclerosis patients: JUSTIFY study results

Abstract Objective To confirm anti–JC virus (JCV) antibody seroprevalence in Portuguese patients with relapsing-remitting multiple sclerosis (RRMS) and to determine their anti-JCV antibody index. Methods JUSTIFY was a retrospective, multicentre study that included 655 RRMS patients tested at least once with the anti-JCV antibody assay STRATIFY JCV DxSelect. Demographic data, multiple sclerosis history and results of the anti-JCV antibody test were collected, along with physicians' reasons for requesting the test and the impact of the results. Results Overall anti-JCV antibody seroprevalence was 60.8% (95% confidence interval, 56.9–64.5). Seroprevalence was associated with higher age (P = .030) and was lower in natalizumab-treated patients (P  Conclusions The study confirmed the high anti-JCV antibody prevalence in Portuguese RRMS patients and its association with age. These data can be used to better understand the benefit-risk profile of natalizumab treatment in Portuguese patients and to support progressive multifocal leukoencephalopathy risk management strategies.