Exposure to IgGs from patients with PV having AuAbs against the ITFGT epitope (i.e., patients ##1, 2 and 3 on Fig. 4) caused significant elevation of PLC, IP3 and DG, i.e., produced a strong agonist-like effect that was similar to that of muscarine. Here, HSPG2 is linked to acquired polycythemia vera.