The sequence consisting of 7 amino acids may be a sequence including any one or more polypeptides selected from the group consisting of RMSRRSN (Arg-Met-Ser-Arg-Arg-Ser-Asn), RRRLNRT (Arg-Arg-Arg-Leu-Asn-Arg-Thr), RMRIRRN (Arg-Met-Arg-Ile-Arg-Arg-Asn), HPHPRPR(His-Pro-His-Pro-Arg-Pro-Arg) and MRNRPKR (Met-Arg-Asn-Arg-Pro-Lys-Arg), but the type of the sequence to be recognized by the autoantibody o