Recently, we have reported that MeV isolates from SSPE patients have hyperfusogenic amino acid changes (e.g., T461I) in the F protein, which enable MeV to spread in the brain by using cell adhesion molecule 1 (CADM1) and CADM2 as cis-acting fusion-triggering molecules. Here, CADM1 is linked to subacute sclerosing panencephalitis.