Expression studies on a novel type 2B variant of the von Willebrand factor gene (R1308L) characterized by defective collagen binding

Abstract

Summary. A novel mutation, R1308L (3923G > T) was present in the heterozygous state in five members of a family with type 2B von Willebrand disease (VWD) characterized by a full set of von Willebrand factor (VWF) multimers in plasma and by the absence of thrombocytopenia before and after desmopressin (DDAVP). The defect (R1308L) was located at the same amino acid position of one of the most common mutations associated with type 2B VWD (R1308C), which is characterized by the loss of high molecular weight VWF multimers (HMWM) in plasma and the occurrence of thrombocytopenia. To understand the mechanisms of this defect, the novel (R1308L) and ÔcommonÕ (R1308C) mutations were expressed in COS-7 cells, either alone or, to mimic the patientsÕ heterozygous state, together with wild-type VWF. R1308L recombinant VWF (rVWF) had a higher affinity for the platelet glycoprotein Iba (GPIba) receptor than wild-type rVWF, R1308C rVWF showing an even higher affinity. A novel finding was that both mutant rVWFs showed a similarly reduced binding to collagen type I and type III in comparison with wild-type rVWF. The latter finding suggests a more important role than recognized so far for the VWF A1 domain in VWF binding to collagen, which may contribute to the in vivo hemostatic defect associated with type 2B VWD.

Clinical and molecular predictors of thrombocytopenia and risk of bleeding in patients with von Willebrand disease type 2B: a cohort study of 67 patients

“…During the 24-month follow-up, platelet count were obtained in all the patients both at baseline and during physiologic or pathologic stress conditions all associated with a short-or long-term rise of plasma VWF. Consistent with previous observations, 9,13,14,33 platelet count were highly variable in VWD2B patients. The prevalence of patients with thrombocytopenia was only 30% at baseline but became almost double (58%) when patients were exposed to stress conditions.…”

“…on May 12, 2018. by guest www.bloodjournal.org From P1266L or R1308L mutations 10,33 : we confirmed that none of them developed thrombocytopenia after administration of the drug. This behavior was strictly correlated to genotype because these patients carried 3 mutations only (P1266Q/L or R1308L).…”

“…Besides mutation R1308L, found in one family (6 patients), 33 more than 1 mutation was found in the remaining 4 families (10 patients), but all shared a substitution of proline 1266. The following nucleotide changes were identified: 3692AϾC (N1231T), 3789GϾA, 3797CϾA (P1266Q) in families 1 and 2, 3686TϾG (V1229G), 3692AϾC (N1231T), 3735GϾA, 3789GϾA, 3797CϾT (P1266L) in family 3, and 3789GϾA, 3797CϾT (P1266L) in family 4, indicating gene conversion with pseudogene.…”

“…Postsurgical thrombocytopenia was observed in 11 of 13 cases; however, platelet count remained normal in 2 patients with the P1266L and R1308L mutations. DDAVP is not recommended in VWD2B, 28 and it was therefore given only to 3 patients with P1266L (formerly diagnosed as type 1 Malmö or New York) or R1308L mutations 10,33 : none of them developed thrombocytopenia after administration of the drug. To sum up, 26 of 34 patients who were exposed to stress situations developed transient thrombocytopenia.…”

Performance and Clinical Utility of a Commercial von Willebrand Factor Collagen Binding Assay for Laboratory Diagnosis of von Willebrand Disease

“…These findings highlight the importance of interpreting VWF:CB activity in the context of all laboratory and clinical data, as is the case with the other VWF tests. We cannot exclude the possibility, however, that low VWF:CB results, in the absence of multimer pattern abnormalities, could point to isolated abnormalities in the VWF gene sequence at domain 1 and/or 3 containing collagen-binding sites (9 ).…”