Although monomeric IgG at therapeutic levels are able to saturate low-affinity FcγR in a dose-dependent manner, it has been suggested that the small amounts of dimeric IgG bind with higher avidity to FcγRs, and therefore constitute the main active component of IVIg mediating FcγR blockade, explaining the immunomodulatory function of high-dose IVIg in ITP, GBS, and CIDP patients (47–51). The gene discussed is FCGR2A; the disease is Guillain-Barre syndrome.