(A) HERV-K env levels in FTD (n = 63), ALS (n = 89) and control (n = 21) serum as measured by ddPCR. (B) HERV-W env levels in FTD (n = 63), ALS (n = 89) and control (n = 21) serum as measured by ddPCR. (C) HERV-K ROC curve for FTD v Con. (D) HERV-K ROC curve for ALS v Con. (E) HERV-K ROC curve for FTD v ALS. Data represent individual patients, mean and SE as error bars, **P < 0.01, ***P < 0.001, ****P < 0.000005.