Mutations in the John Cunningham virus VP1 gene could predispose to the development of progressive multifocal leukoencephalopathy in multiple sclerosis patients undergoing treatment with natalizumab

Background: Patients with Multiple Sclerosis (MS) undergoing treatment with natalizumab (NTZ) are at risk of developing progressive multifocal leukoencephalopathy (PML) due to the reactivation of John Cunningham (JC) virus. A relevant characteristic among PML cases is the development of single nucleotide mutations in the VP1 gene of the causal JC virus. The identification of such mutations in timely manner can provide valuable infor-mation for MS management. Objective: To identify mutations along the JC virus VP1 gene in MS patients undergoing treatment with NTZ, and correlate them with anti-JC virus antibody index. Methods: Eighty-eight MS patients, one hundred twenty controls, and six patients with diagnosis of Human Immunodeficiency Virus (HIV) with and without secondary PML were included. JC virus was identified in pe-ripheral blood mononuclear cells and cerebrospinal fluid by PCR. Amplification and sequencing of the entire length of the VP1 gene were performed in all positive clinical samples. Results: In MS cases no mutations were observed in the JC virus VP1 gene, but it was positive in HIV controls with PML. Interestingly, the JC virus VP1 gene sequence derived from the HIV patients exhibited a non-silent sub-stitution in position 186 (G-* C), leading to an amino acid change (Lys-* Asp). We did not find correlation between anti-JC virus antibody index and DNA viral detection. Conclusions: . The identification of single nucleotide mutants in the JC virus VP1 gene might be an early pre-dictive marker to PML for efficient patient treatment and follow-up.