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We observed a 55-year-old Italian man who presented with mucosal and cutaneous bleeding. Results of his blood analysis showed low levels of von Willebrand factor (VWF) antigen and VWF activity (both VWF ristocetin cofactor and VWF collagen binding), mild thrombocytopenia, increased ristocetin-induced platelet aggregation, and a deficiency of high-molecular-weight multimers, all typical phenotypic hallmarks of type 2B von Willebrand disease (VWD). The analysis of the VWF gene sequence revealed heterozygous in cis mutations: (1) c.2771G>A and (2) c.6532G>T substitutions in the exons 21 and 37, respectively. The first mutation causes the substitution of an Arg residue with a Gln at position 924, in the D′D3 domain. The second mutation causes an Ala to Ser substitution at position 2178 in the D4 domain. The patient’s daughter did not present the same fatherly mutations but showed only the heterozygous polymorphic c.3379C>T mutation in exon 25 of the VWF gene causing the p.P1127S substitution, inherited from her mother. The in vitro expression of the heterozygous in cis VWF mutant rVWFWT/rVWF924Q-2178S confirmed and recapitulated the ex vivo VWF findings. Molecular modeling showed that these in cis mutations stabilize a partially stretched and open conformation of the VWF monomer. Transmission electron microscopy and atomic force microscopy showed in the heterozygous recombinant form rVWFWT/rVWF924Q-2178S a stretched conformation, forming strings even under static conditions. Thus, the heterozygous in cis mutations 924Q/2178S promote conformational transitions in the VWF molecule, causing a type 2B–like VWD phenotype, despite the absence of typical mutations in the A1 domain of VWF.

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy caused by a hereditary or immune-mediated deficiency of the enzyme ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13). TTPs are caused by the following pathophysiological mechanisms: (1) the presence of inhibitory autoantibodies against ADAMTS13; and (2) hereditary mutations of the ADAMTS13 gene, which is present on chromosome 9. In both syndromes, TTP results from a severe deficiency of ADAMTS13, which is responsible for the impaired proteolytic processing of high-molecular-weight von Willebrand factor (HMW-VWF) multimers, which avidly interact with platelets and subendothelial collagen and promote tissue and multiorgan ischemia. Although the acute presentation of the occurring symptoms in acquired and hereditary TTPs is similar (microangiopathic hemolytic anemia, thrombocytopenia, and variable ischemic end-organ injury), their intensity, incidence, and precipitating factors are different, although, in both forms, a severe ADAMTS13 deficiency characterizes their physiopathology. This review is aimed at exploring the possible factors responsible for the different clinical and pathological features occurring in hereditary and immune-mediated TTPs.

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