Human endothelial cells synthesize and release ADAMTS-13

A functional calcium-binding site in the metalloprotease domain of ADAMTS13

ADAMTS13 regulates the multimeric size of von Willebrand factor (VWF). Its function is highly dependent upon Ca(2+) ions. Using the initial rates of substrate (VWF115, VWF residues 1554-1668) proteolysis by ADAMTS13 preincubated with varying Ca(2+) concentrations, a high-affinity functional ADAMTS13 Ca(2+)-binding site was suggested with K(D(app)) of 80 muM (+/- 15 muM) corroborating a previously reported study. When Glu83 or Asp173 (residues involved in a predicted Ca(2+)-binding site in the ADAMTS13 metalloprotease domain) were mutated to alanine, Ca(2+) dependence of proteolysis of the substrate was unaffected. Consequently, we sought and identified a candidate Ca(2+)-binding site in proximity to the ADAMTS13 active site, potentially comprising Glu184, Asp187, and Glu212. Mutagenesis of these residues within this site to alanine dramatically attenuated the K(D(app)) for Ca(2+) of ADAMTS13, and for D187A and E212A also reduced the V(max) to approximately 25% of normal. Kinetic analysis of the Asp187 mutant in the presence of excess Ca(2+) revealed an approximately 13-fold reduction in specificity constant, k(cat)/K(m), contributed by changes in both K(m) and k(cat). These results were corroborated using plasma-purified VWF as a substrate. Together, our results demonstrate that a major influence of Ca(2+) upon ADAMTS13 function is mediated through binding to a high-affinity site adjacent to its active site cleft.

Effects of naturally occurring mutations in CUB-1 domain on synthesis, stability, and activity of ADAMTS-13

INTRODUCTION

Upon stimulation, endothelial cells release von Willebrand factor (VWF) in the unusually large (UL) and hyperactive forms that are rapidly cleaved by ADAMTS-13. Mutations in the ADAMTS13 gene result in ULVWF-mediated thrombosis found in patients with familial thrombotic thrombocytopenia purpura (TTP). ADAMTS-13 fits in the consensus of the ADAMTS family metalloproteases, but also contains two unique C- terminal CUB domains. Studying mutations in CUB domains could provide insights into the functional role of these domains.

METHODS

Three naturally occurring mutations (C1213Y, W1245del and K1256FS) in the CUB-1 domain found in patients with TTP were expressed in Hela cells. The secretion, stability and VWF-cleaving activity of the mutants under static and flow conditions were examined.

RESULTS

The mutations impaired secretion of ADAMTS-13 to apical surface, but not to extracellular matrix of transfected Hela cells. C1213Y and K1256FS also accelerated, whereas W1245del delayed, extracellular degradation of the mutants. The mutations also resulted in a moderate decrease in cleaving plasma VWF under static conditions. However, the mutated ADAMTS-13 bound to VWF substrate similarly as the wild-type metalloprotease and remained active in cleaving (UL)VWF under flow conditions.

CONCLUSIONS

The CUB-1 domain is critical for ADAMTS-13 secretion and stability upon secretion. ADAMTS-13 deficiency found in TTP patients could be resulted from reduced ADAMTS-13 secretion and, in the case of C1213Y and K1256FS accelerated degradation. W1245del is highly resistant to degradation and active in cleaving VWF.

N-Glycans of ADAMTS13 modulate its secretion and von Willebrand factor cleaving activity

Severe deficiency of ADAMTS13, a plasma metalloprotease, leads to thrombotic thrombocytopenic purpura. ADAMTS13 contains 10 putative N-glycosylation sites in or near its metalloprotease sequence, spacer region, thrombospondin type 1 repeat no. 4 (TSR no. 4), and CUB domains. Tunicamycin treatment markedly decreased the secretion of ADAMTS13 into the culture medium of transfected cells. Nevertheless, the protease was efficiently secreted from N-acetylglucosaminyltransferase I-deficient Lec1 Chinese hamster ovary cells, indicating that N-glycosylation in the endoplasmic reticulum, but not the conversion of oligomannose to complex N-glycans in the Golgi complex, is important for secretion. However, ADAMTS13 with oligomannose N-glycans cleaved its substrate, von Willebrand factor (VWF) multimers, less effectively, with a higher K(m) but similar k(cat) value. In mutagenesis analysis, decreased secretion and VWF cleaving activity was observed with the N146Q and N828Q mutants, while decreased secretion only was observed with the N552Q mutant of ADAMTS13. Enzymatic removal of N-glycans from ADAMTS13 did not affect its VWF cleaving activity. Thus, N-glycosylation is necessary for efficient secretion of ADAMTS13, while conversion of the N-glycans from oligomannose to complex type in the Golgi complex enhances the proteolytic activity of the protease toward VWF multimers. After its secretion, ADAMTS13 does not require N-glycans for its VWF cleaving activity.

Correction of ADAMTS13 deficiency by in utero gene transfer of lentiviral vector encoding ADAMTS13 genes

Deficiency of A Disintegrin And Metalloprotease with ThromboSpondin (ADAMTS13) results in thrombotic thrombocytopenic purpura (TTP). Plasma infusion or exchange is the only effective treatment to date. We show in this study that an administration of a self-inactivating lentiviral vector encoding human full-length ADAMTS13 and a variant truncated after the spacer domain (MDTCS) in mice by in utero injection at embryonic days 8 and 14 resulted in detectable plasma proteolytic activity (approximately 5-70%), which persisted for the length of the study (up to 24 weeks). Intravascular injection via a vitelline vein at E14 was associated with significantly lower rate of fetal loss than intra-amniotic injection, suggesting that the administration of vector at E14 may be a preferred gestational age for vector delivery. The mice expressing ADAMTS13 and MDTCS exhibited reduced sizes of von Willebrand factor (vWF) compared to the Adamts13(-/-) mice expressing enhanced green fluorescent protein (eGFP). Moreover, the mice expressing both ADAMTS13 and MDTCS showed a significant prolongation of ferric chloride-induced carotid arterial occlusion time as compared to the Adamts13(-/-) expressing eGFP. The data demonstrate the successful correction of the prothrombotic phenotypes in Adamts13(-/-) mice by a single in utero injection of lentiviral vectors encoding human ADAMTS13 genes, providing the basis for developing a gene therapy for hereditary TTP in humans.

[Haemolytic uremic syndrome and thrombotic thrombocytopenic purpura: classification based on molecular etiology and review of recent developments in diagnostics]

Haemolytic uremic syndrome and thrombotic thrombocytopenic purpura are overlapping clinical entities based on historical classification. Recent developments in the unfolding of the pathomechanisms of these diseases resulted in the creation of a molecular etiology-based classification. Understanding of some causative relationships yielded detailed diagnostic approaches, novel therapeutic options and thorough prognostic assortment of the patients. Although haemolytic uremic syndrome and thrombotic thrombocytopenic purpura are rare diseases with poor prognosis, the precise molecular etiology-based diagnosis might properly direct the therapy of the affected patients. The current review focuses on the theoretical background and detailed description of the available diagnostic possibilities, and some practical information necessary for the interpretation of their results.

Pathogenesis of thrombotic microangiopathies

Profound thrombocytopenia and microangiopathic hemolytic anemia characterize thrombotic microangiopathy, which includes two major disorders: thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). TTP has at least three types: congenital or familial, idiopathic, and nonidiopathic. The congenital and idiopathic TTP syndromes are caused primarily by deficiency of ADAMTS13, owing to mutations in the ADAMTS13 gene or autoantibodies that inhibit ADAMTS13 activity. HUS is similar to TTP, but is associated with acute renal failure. Diarrhea-associated HUS accounts for more than 90% of cases and is usually caused by infection with Shiga-toxin-producing Escherichia coli (O157:H7). Diarrhea-negative HUS is associated with complement dysregulation in up to 50% of cases, caused by mutations in complement factor H, membrane cofactor protein, factor I or factor B, or by autoantibodies against factor H. The incomplete penetrance of mutations in either ADAMTS13 or complement regulatory genes suggests that precipitating events or triggers may be required to cause thrombotic microangiopathy in many patients.

Unbalanced expression of ADAMTS13 and von Willebrand factor in mouse endotoxinemia

INTRODUCTION

Secondary ADAMTS13 deficiency may occur in septic patients. The expression of ADAMTS13 in mouse endotoxinemia was studied.

METHODS

The blood and mRNA expression levels of ADAMTS13 and von Willebrand factor were measured in lipopolysaccharide-injected mice.

RESULTS

The plasma ADAMTS13 activity in wild-type mice was significantly decreased at 2 h after lipopolysaccharide injection, and this decrease in ADAMTS13 activity preceded the decrease in ADAMTS13 mRNA expression in the liver and continued for 24 h. However, no decreases in the plasma ADAMTS13 activity after lipopolysaccharide injection were observed in mice pretreated with a neutrophil elastase inhibitor or in plasminogen-deficient mice, suggesting that the decrease in ADAMTS13 activity was processed efficiently by the coordinated actions of plasmin and neutrophil elastase. von Willebrand factor mRNA was abundantly expressed in the lung and moderately in the kidney, but showed relatively low expression in the liver without lipopolysaccharide injection. However, von Willebrand factor mRNA expression in the liver was significantly increased after lipopolysaccharide injection and this high expression level continued for 24 h after the injection. The von Willebrand factor and ADAMTS13 mRNA expression levels in these organs changed in the opposite manners following lipopolysaccharide administration. Furthermore, the blood von Willebrand factor level increased after lipopolysaccharide administration, in contrast to the decrease in the blood ADMTS13 level after lipopolysaccharide administration.

CONCLUSION

These data suggest that imbalance between the blood von Willebrand factor and ADAMTS13 levels may occur in endotoxinemia, and that this may partly contribute to the thrombotic state associated with endotoxinemia.

The cooperative activity between the carboxyl-terminal TSP1 repeats and the CUB domains of ADAMTS13 is crucial for recognition of von Willebrand factor under flow

ADAMTS13 cleaves von Willebrand factor (VWF) between Tyr(1605) and Met(1606) residues at the central A2 subunit. The amino-terminus of ADAMTS13 protease appears to be sufficient to bind and cleave VWF under static and denatured condition. However, the role of the carboxyl-terminus of ADAMTS13 in substrate recognition remains controversial. Present study demonstrates that ADAMTS13 cleaves VWF in a rotation speed- and protease concentration-dependent manner on a mini vortexer. Removal of the CUB domains (delCUB) or truncation after the spacer domain (MDTCS) significantly impairs its ability to cleave VWF under the same condition. ADAMTS13 and delCUB (but not MDTCS) bind VWF under flow with dissociation constants (K(D)) of about 50 nM and about 274 nM, respectively. The isolated CUB domains are neither sufficient to bind VWF detectably nor capable of inhibiting proteolytic cleavage of VWF by ADAMTS13 under flow. Addition of the TSP1 5-8 (T5-8CUB) or TSP1 2-8 repeats (T2-8CUB) to the CUB domains restores the binding affinity toward VWF and the inhibitory effect on cleavage of VWF by ADAMTS13 under flow. These data demonstrate directly and quantitatively that the cooperative activity between the middle carboxyl-terminal TSP1 repeats and the distal carboxyl-terminal CUB domains may be crucial for recognition and cleavage of VWF under flow.

Thrombotic thrombocytopenic purpura: a thrombotic disorder caused by ADAMTS13 deficiency

A serious disorder with characteristic microvascular thrombosis involving the brain and other organs, thrombotic thrombocytopenic purpura (TTP) typically presents with thrombocytopenia, hemolysis with schistocytes on blood smears, and mental changes or seizures. It may progress rapidly to a fatal end if the patient is not treated immediately with plasma. Recent advances have shown that TTP is caused by deficiency of a circulating, von Willebrand factor cleaving metalloprotease, ADAMTS13. This new knowledge will provide clues to improve the diagnosis and management of this intriguing disease.

An IAP retrotransposon in the mouse ADAMTS13 gene creates ADAMTS13 variant proteins that are less effective in cleaving von Willebrand factor multimers

Severe deficiency of ADAMTS13, a von Willebrand factor (VWF)-cleaving metalloprotease, causes thrombotic thrombocytopenic purpura. When analyzed with VWF multimers, but not with an abbreviated VWF peptide (VWF73) as the substrate, the plasma ADAMTS13 activity levels of mouse strains segregated into a high and a low group that differed by approximately 10 fold. Low ADAMTS13 activity was detected in mice containing 2 alleles of intracisternal A-type particle (IAP) retrotransposon sequence in the ADAMTS13 gene. Molecular cloning of mouse ADAMTS13 identified 2 truncated variants (IAP-a and IAP-b) in the low-activity mice. Both of the IAP variants lacked the 2 carboxyl terminus thrombospondin type 1 repeat (TSR) and CUB domains of full-length ADAMTS13. The IAP-b variant also had splicing abnormalities affecting the spacer domain sequence and had miniscule enzymatic activity. Compared with full-length ADAMTS13, the IAP-a variant was approximately one ninth as active in cleaving VWF multimers but was only slightly less active in cleaving VWF73 peptide. Recombinant human ADAMTS13 was also less effective in cleaving VWF multimers than VWF73 when the C-terminal TSR sequence was deleted. In summary, the carboxyl terminus TSR sequence is important for cleaving VWF multimers. Assay results should be interpreted with caution when peptide substrates are used for analysis of variant ADAMTS13 proteins.

Podocytes express ADAMTS13 in normal renal cortex and in patients with thrombotic thrombocytopenic purpura

Congenital thrombotic thrombocytopenic purpura (TTP) is associated with ADAMTS13 mutations. The major site of ADAMTS13 synthesis is the liver. Expression in other tissues, and in TTP, has not been shown. In this study, ADAMTS13 protein expression was investigated in normal kidney and in renal tissue from two TTP patients, with a compound heterozygous mutation (P353L and P457L) and a homozygous mutation (4143insA). Real-time polymerase chain reaction demonstrated ADAMTS13 mRNA in normal kidney. ADAMTS13 was detected in the glomeruli and tubuli of normal and TTP kidney using anti-ADAMTS13 antibodies. In the glomeruli, expression was localised to podocytes (as demonstrated by counterstaining with two podocyte markers) and endothelium. Similar distribution was detected in the TTP kidneys. Electron microscopy detected ADAMTS13 in podocytes, endothelium and glomerular basement membrane. Cultured human podocytes expressed ADAMTS13 mRNA and protein, and podocyte lysate exhibited von Willebrand factor-cleaving activity. Mutation expression studies of the P353L and P457L mutations showed partially impaired secretion and lower activity of the secreted mutants. Impaired secretion has previously been shown for the 4143insA mutation. Podocyte-derived ADAMTS13 may offer local protection in the high-shear microcirculation of the glomerulus. The mutations in the two TTP patients studied enabled protein expression in the podocytes but affected protease secretion.

ADAMTS13 activity to antigen ratio in physiological and pathological conditions associated with an increased risk of thrombosis

The plasma metalloprotease ADAMTS13 (A Disintegrin And Metalloprotease with ThromboSpondin type 1 motif 13) cleaves prothrombotic ultralarge multimers of the platelet-adhesive protein von Willebrand factor (ULVWF) into less active multimers that promote haemostasis in injured blood vessels. When the enzyme is dysfunctional or undetectable, circulating ULVWF may cause massive intravascular aggregation of platelets and thrombotic thrombocytopenic purpura. This study compared ADAMTS13 antigen and activity in a large set of plasmas collected from subjects with various conditions of health and disease, most of which were associated with an increased thrombotic tendency. Pathological conditions were liver cirrhosis (n = 90), inflammatory bowel disease (n = 44) and cardiac surgery (n = 30). Healthy conditions were pregnancy (n = 42), oral contraceptive intake (n = 33) and the neonatal state (n = 41). Normal individuals of different ages were taken as controls (n = 132). The antigen assay showed less variability than the collagen binding-based activity assay. Antigen values correlated well with activity in normal individuals, but were discrepant to various degrees in neonates, pregnancies of later maternal age and cardiac surgery. No discrepancies were noted in liver cirrhosis and inflammatory bowel disease, which were both associated with low-plasma levels of ADAMTS13. The parallel measurement of ADAMTS13 activity and antigen provides a new tool for understanding the behaviour of the VWF cleaving protease in health and disease.

ADAMTS13 assays and ADAMTS13-deficient mice

PURPOSE OF REVIEW

Thrombotic thrombocytopenic purpura can be induced by acquired or congenital deficiency of the plasma von Willebrand factor-cleaving protease, ADAMTS13. Measurement of ADAMTS13 activity is important for the diagnosis and treatment of microangiopathies including thrombotic thrombocytopenic purpura. Phenotypic analysis of mice lacking the Adamts13 gene is valuable for understanding the pathogenesis of microangiopathies.

RECENT FINDINGS

The minimum substrate for ADAMTS13 activity was identified as 73 amino acid residues in the A2 domain of von Willebrand factor, called VWF73. Several new assays have been developed using this sequence. The VWF73-based assays are rapid, quantitative, and easy to handle, and are well correlated with the measures from previous assays. Mice lacking the Adamts13 gene were produced. The mice were viable and fertile. They showed a prothrombotic state but no symptoms of spontaneous thrombocytopenia, hemolytic anemia, or microvascular thrombosis were observed.

SUMMARY

VWF73-based ADAMTS13 assays will significantly facilitate the accurate diagnosis of microangiopathies and contribute to the improved clinical treatment of these diseases. Accumulated clinical information on patients with ADAMTS13 deficiency and mice lacking the Adamts13 gene indicates that additional environmental or genetic susceptibility factors are required to trigger thrombotic thrombocytopenic purpura.

Further characterization of ADAMTS-13 inactivation by thrombin

BACKGROUND

The multimeric size and platelet-tethering function of von Willebrand factor (VWF) are modulated by the plasma metalloprotease, a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS-13). In vitro ADAMTS-13 is susceptible to proteolytic inactivation by thrombin.

OBJECTIVES

In this study, we aimed to characterize the inactivation of ADAMTS-13 by thrombin and to assess its physiological significance.

METHODS AND RESULTS

By N-terminal sequencing of cleavage products, and by mutagenesis, we identified the principal thrombin cleavage sites in ADAMTS-13 as R257 and R1176. Using a library of 76 thrombin mutants, we highlighted the functional importance of exosite I on thrombin in the proteolysis of ADAMTS-13. Proteolysis of ADAMTS-13 by thrombin caused an 8-fold reduction in its affinity for VWF that contributed to its loss of VWF-cleaving function. Intriguingly, thrombin-cleaved ADAMTS-13 both bound and proteolyzed a short recombinant VWF A2 domain substrate (VWF115) normally. Following activation of coagulation in normal plasma, endogenous ADAMTS-13, but not added ADAMTS-13, appeared resistant to coagulation-induced fragmentation. An estimation of the K(m) for ADAMTS-13 proteolysis by thrombin was appreciably higher than the physiological concentration of ADAMTS-13. This was corroborated by the comparatively low affinity of ADAMTS-13 for thrombin (K(D) 95 nM).

CONCLUSIONS

Together, our data suggest that ADAMTS-13 is protected from rapid proteolytic inactivation by thrombin in normal plasma. Whether this remains the case under pathological situations involving elevated/sustained generation of thrombin remains unclear.

Structural and functional correlation of ADAMTS13

PURPOSE OF REVIEW

ADAMTS13 represents a landmark in a journey that began over 80 years ago with a single clinical case. Thrombotic thrombocytopenic purpura exemplifies how von Willebrand factor can be responsible for life-threatening thrombosis. This review summarizes recent progress on ADAMTS13, which prevents this deadly event.

RECENT FINDINGS

Recent advances are summarized in four main areas. First, the core ADAMTS13-binding site is contained in a short sequence in the A2 domain, but other domains affect this interaction. Mutations from thrombotic thrombocytopenic purpura and von Willebrand disease provide clues for the structural prerequisites and regulation of von Willebrand factor cleavage. Second, studies are unraveling the reasons why urea, BaCl2, and low ionic strength are required to cleave von Willebrand factor under static conditions. Third, studies on thrombotic thrombocytopenic purpura and ADAMTS13-knockout mice suggest that ADAMTS13 deficiency alone may not be sufficient to cause thrombotic thrombocytopenic purpura. Finally, ADAMTS13 could be an antithrombotic agent for thrombotic thrombocytopenic purpura and other thrombotic conditions.

SUMMARY

Study of ADAMTS13 has exploded since this metalloprotease was characterized. This knowledge reveals the nature of ADAMTS13's interaction with von Willebrand factor and the pathogenesis of clinical thrombotic thrombocytopenic purpura, especially in relation to ADAMTS13.

Hepatic stellate cell damage may lead to decreased plasma ADAMTS13 activity in rats

ADAMTS13 is gaining attention, because its deficiency causes thrombotic thrombocytopenic purpura. Although its regulatory mechanism is not fully understood, we wondered if hepatic stellate cells (HSCs) play a role, because ADAMTS13 mRNA is exclusively expressed in the liver and primarily in HSCs. Plasma ADAMTS13 activity was markedly reduced in dimethylnitrosamine-treated rats, where HSC apoptosis is an essential event, but not in carbon tetrachloride- or thioacetamide-treated rats without HSC apoptosis. Furthermore, plasma ADAMTS13 activity was also reduced in 70% hepatectomized rats, where HSC loss occurs. These results suggest that HSC may be involved in the regulation of plasma ADAMTS13 activity.

ADAMTS13 and microvascular thrombosis

Interaction between platelet and von Willebrand factor, a circulating adhesive glycoprotein, is essential for hemostasis under the high shear environments of arterioles and capillaries. If unregulated, this interaction may lead to unwarranted platelet thrombosis. ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motif, number 13), a plasma zinc metalloprotease synthesized primarily in the stellate cells of the liver, cleaves shear stress-activated von Willebrand factor, thereby preventing the occurrence of von Willebrand factor-platelet interaction in the circulation. A profound deficiency of ADAMTS13, due to genetic mutations or autoimmune inhibition, results in intravascular von Willebrand factor platelet aggregation and widespread microvascular thrombosis characteristic of thrombotic thrombocytopenic purpura. Cloning of ADAMTS13 and structure-function analyses of the enzyme are leading to exciting advances in the diagnosis and therapy of this hitherto mysterious disease.

Conformational stability and domain unfolding of the Von Willebrand factor A domains

Von Willebrand factor (VWF), a multimeric multidomain glycoprotein secreted into the blood from vascular endothelial cells, initiates platelet adhesion at sites of vascular injury. This process requires the binding of platelet glycoprotein Ib-IX-V to the A1 domain of VWF monomeric subunits under fluid shear stress. The A2 domain of VWF monomers contains a proteolytic site specific for a circulating plasma VWF metalloprotease, A Disintegrin and Metalloprotease with Thrombospondin motifs, member #13 of the ADAMTS enzyme family (ADAMTS-13), that functions to reduce adhesiveness of newly released, unusually large (UL), hyperactive forms of VWF. Shear stress assists ADAMTS-13 proteolysis of ULVWF multimers allowing ADAMTS-13 cleavage of an exposed peptide bond in the A2 domain. Shear stress may induce conformational changes in VWF, and even unfold regions of VWF monomeric subunits. We used urea as a surrogate for shear to study denaturation of the individual VWF recombinant A domains, A1, A2, and A3, and the domain triplet, A1-A2-A3. Denaturation was evaluated as a function of the urea concentration, and the intrinsic thermodynamic stability of the domains against unfolding was determined. The A1 domain unfolded in a 3-state manner through a stable intermediate. Domains A2 and A3 unfolded in a 2-state manner from native to denatured. The A1-A2-A3 triple domain unfolded in a 6-state manner through four partially folded intermediates between the native and denatured states. Urea denaturation of A1-A2-A3 was characterized by two major unfolding transitions: the first corresponding to the simultaneous complete unfolding of A2 and partial unfolding of A1 to the intermediate state; and the second corresponding to the complete unfolding of A3 followed by gradual unfolding of the intermediate state of A1 at high urea concentration. The A2 domain containing the cleavage site for ADAMTS-13 was the least stable of the three domains and was the most susceptible to unfolding. The low stability of the A2 domain is likely to be important in regulating the exposure of the A2 domain cleavage site in response to shear stress, ULVWF platelet adherence, and the attachment of ADAMTS-13 to ULVWF.

Novel ADAMTS-13 mutations in an adult with delayed onset thrombotic thrombocytopenic purpura

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) is associated with congenital and acquired deficiency of ADAMTS-13, a metalloprotease that cleaves von Willebrand factor (VWF) and reduces its adhesive activity. Mutations throughout the ADAMTS13 gene have been identified in congenital TTP patients, most of whom have initial episodes during infancy or in early childhood.

PATIENTS AND METHODS

We report the case of an adult male who was diagnosed with idiopathic thrombocytopenic purpura at age 34, and with TTP 14 years later. The patient was compound heterozygous for an 18 bp in-frame deletion (C365del) in the disintegrin domain and a point mutation of R1060W in the seventh thrombospondin domain of the ADAMTS-13 gene.

CONCLUSIONS

In vitro studies found that C365del and R1060W severely impair ADAMTS-13 synthesis in transfected Hela cells, whereas the deletion mutant also failed to cleave VWF under static and flow conditions.