In all cases the expressed BCRs were encoded by VH1-69/Vk3D-20 genes whose light chains carried complementarity determining region 3 (CDR3) sequences homologous to canonical RFs of MC patients as well as to antibodies against the E2 envelope protein of HCV (Supplementary Table 2), a signature of BCRs expressed in lymphoproliferative disorders secondary to HCV infection (3, 4). The gene discussed is ERVW-1; the disease is lymphoproliferative syndrome.