Values of VWF–GPIb-α/BC and correlation with platelet count. (A) Distribution of the values of VWF–GPIb-α/BC as detected by nanobody in 6 different groups of persons (from the left to the right): 40 normal subjects (indicated as normal controls); 12 VWD1 patients with multimeric pattern A (VWD1 HMWM [A]); 14 VWD2A patients with multimeric patterns C or D (VWD2A no HMWM [C-D]); 16 VWD2B patients with P1266Q/L and R1308L mutations with multimeric pattern A (VWD2B HMWM [A]); 51 VWD2B with multimeric patterns B or C or D (VWD2B no HMWM [B, C, D]); 10 VWD2M patients with multimeric pattern B (VWD2M no HMWM [B]). Note that VWF–GPIb-α/BC is lower than normal in VWD1 and VWD2A with mutations outside VWF A1 domain and is higher than normal in VWD2B and VWD2M with mutations within VWF A1 domain. Interestingly, the gain-of-function P1266Q/L and R1308L mutations characterized by the presence of all the multimers (pattern A) show VWF–GPIb-α/BC values similar to controls. (B) Relationship between VWF–GPIb-α/BC values by nanobody (vertical axis) and platelet count at baseline (horizontal axis) in the 67 patients with VWD2B. Patients with normal HMW multimers and P1266Q/L and R1308L mutations have normal values of VWF–GPIb-α/BC (○), whereas VWD2B patients with loss of HMW multimers and H1268D, R1306Q, R1308C/L, I309V, V1316H, P1337L, and R1341Q/W mutations have increased values of VWF–GPIb-α/BC (●). Note that an inverse relationship is present mainly in the second group of patients.