[The tooth: A marker of developmental abnormalities]

Tooth formation results from specific epithelial-mesenchymal interactions, which summarize a number of developmental processes. Tooth anomalies may thus reflect subclinical diseases of the kidney, bone and more broadly of the mineral metabolism, skin or nervous system. Odontogenesis starts from the 3rd week of intrauterine life by the odontogenic orientation of epithelial cells by a first PITX2 signal. The second phase is the acquisition of the number, shape, and position of teeth. It depends on multiple transcription and growth factors (BMP, FGF, SHH, WNT). These ecto-mesenchymal interactions guide cell migration, proliferation, apoptosis and differentiation ending in the formation of the specific dental mineralized tissues. Thus, any alteration will have consequences on the tooth structure or shape. Resulting manifestations will have to be considered in the patient phenotype and the multidisciplinary care, but also may contribute to identify the altered genetic circuity.

Oro-dental phenotyping and report of three families with RELT-associated amelogenesis imperfecta

Amelogenesis imperfecta (AI) is a group of rare genetic conditions characterized by quantitative and/or qualitative tooth enamel alterations. AI can manifest as an isolated trait or as part of a syndrome. Recently, five biallelic disease-causing variants in the RELT gene were identified in 7 families with autosomal recessive amelogenesis imperfecta (ARAI). RELT encodes an orphan receptor in the tumor necrosis factor (TNFR) superfamily expressed during tooth development, with unknown function. Here, we report one Brazilian and two French families with ARAI and a distinctive hypomineralized phenotype with hypoplastic enamel, post-eruptive enamel loss, and occlusal attrition. Using Next Generation Sequencing (NGS), four novel RELT variants were identified (c.120+1G>A, p.(?); c.120+1G>T, p.(?); c.193T>C, p.(Cys65Arg) and c.1260_1263dup, p.(Arg422Glyfs*5)). Our findings extend the knowledge of ARAI dental phenotypes and expand the disease-causing variants spectrum of the RELT gene.

Vasorin plays a critical role in vascular smooth muscle cells and arterial functions

Within the cardiovascular system, the protein vasorin (Vasn) is predominantly expressed by vascular smooth muscle cells (VSMCs) in the coronary arteries and the aorta. Vasn knockout (Vasn^-/- ) mice die within 3 weeks of birth. In the present study, we investigated the role of vascular Vasn expression on vascular function. We used inducible Vasn knockout mice (Vasn^{CRE-ERT KO} and Vasn^{SMMHC-CRE-ERT2 KO} , in which respectively all cells or SMCs only are targeted) to analyze the consequences of total or selective Vasn loss on vascular function. Furthermore, in vivo effects were investigated in vitro using human VSMCs. The death of Vasn^{CRE-ERT KO} mice 21 days after tamoxifen injection was concomitant with decreases in blood pressure, angiotensin II levels, and vessel contractibility to phenylephrine. The Vasn^{SMMHC-CRE-ERT2 KO} mice displayed concomitant changes in vessel contractibility in response to phenylephrine and angiotensin II levels. In vitro, VASN deficiency was associated with a shift toward the SMC contractile phenotype, an increase in basal intracellular Ca²⁺ levels, and a decrease in the SMCs' ability to generate a calcium signal in response to carbachol or phenylephrine. Additionally, impaired endothelium-dependent relaxation (due to changes in nitric oxide signaling) was observed in all Vasn knockout mice models. Our present findings highlight the role played by Vasn SMC expression in the maintenance of vascular functions. The mechanistic experiments suggested that these effects are mediated by SMC phenotype switching and changes in intracellular calcium homeostasis, angiotensin II levels, and NO signaling.

OSCEGame: A serious game for OSCE training

BACKGROUND

Objective Structured Clinical Examinations (OSCEs) are amongst the most anxiety-provoking competency assessment methods. An online serious game (OSCEGame) was developed and implemented within the OSCE curriculum. This study aimed to evaluate the usefulness of this serious game on preparedness and reducing OSCE-related stress.

METHODS

A serious game was designed to help dental students train for OSCEs. Two game courses (4 stations each) were designed according to year of undergraduate training (4^th and 5^th year), based on 6 pre-existing multi-competency OSCE stations. The OSCEGame was available online on a learning platform 4 to 6 weeks before the summative OSCEs. Game use was evaluated by analysing connection data. Preparedness, stress and time management skills were assessed using a questionnaire following the summative OCSEs. The results of 4^th -year students (OSCE naive population) were compared to those of 5^th -year students to assess usefulness and benefits of such preparation method.

RESULTS

In total, 97% and 60% of the students in 4^th year and 5^th year, respectively, used the game. The game was seen as an essential preparation tool to reduce anxiety (for 60% of all students) and increase time management skills (65% of all students). However, significant differences were observed between 4^th- and 5^th -year students (anxiety reduction: 65% vs. 22%, p < 0.001; time management skills: 59% vs. 41%, p < 0.05) suggesting that it is most useful for OSCE naive students.

CONCLUSION

This serious game is a useful time efficient online tool, for OSCE preparation, especially in OSCE naive students.

From Vascular Smooth Muscle Cells to Folliculogenesis: What About Vasorin?

First described in 1988, vasorin (VASN) is a transmembrane glycoprotein expressed during early mouse development, and with a less extent, in various organs and tissues (e.g., kidney, aorta, and brain) postnatally. Vasn KO mice die after 3 weeks of life from unknown cause(s). No human disease has been associated with variants of this gene so far, but VASN seems to be a potential biomarker for nephropathies and tumorigenesis. Its interactions with the TGF-β and Notch1 pathways offer the most serious assumptions regarding VASN functions. In this review, we will describe current knowledge about this glycoprotein and discuss its implication in various organ pathophysiology.

Type 2M vWD Resulting from a Lysine Deletion within a Four Lysine Residue Repeat in the A1 Loop of von Willebrand Factor

Type 1 von Willebrand disease is characterized by a decreased plasma concentration of functionally normal von Willebrand factor (vWF) whereas type 2M is characterised by an abnormal vWF displaying decreased affinity for platelets. In these two types of patients, the multimeric structure of vWF is normal.

We report here the identification, in two unrelated families from the UK and Algeria, of an in-frame 3 bp deletion, at the heterozygous state, resulting in the deletion of a lysine residue within a four lysine repeat at position 642-645 of the mature vWF subunit (del K1405-1408 in prepro vWF). The patients who have a discrepancy between vWF antigen level and vWF ristocetin cofactor activity exhibited decreased ristocetin-induced binding but only a slight decrease in the percentage of high molecular weight (HMW) multimers in plasma.

Recombinant vWF harbouring this deletion did not bind to platelet GPIb in the presence of ristocetin or botrocetin although the protein is multimerized. Consequently, this lysine deletion was considered as a type 2M vWD mutation.

Type 2N von Willebrand Disease: Rapid Genetic Diagnosis of G2811A (R854Q), C2696T (R816W), T2701A (H817Q) and G2823T (C858F) – Detection of a Novel Candidate Type 2N Mutation: C2810T (R854W)

The majority of patients with type 2N von Willebrand disease (VWD type 2N) have mutations in the region of the von Willebrand factor (VWF) gene encoding the factor VIII binding domain of VWF. Two mutations predominate among VWD type 2N patients: G2811A and C2696T, which respectively bring about the amino acid substitutions R854Q and R816W in VWF. Several other mutations have been found in VWD type 2N, including T2701A (H817Q) and G2823T (C858F). We have developed a genetic test which permits rapid screening for these four mutations in a single polymerase chain reaction (PCR). The test employs induced heteroduplex formation using two universal heteroduplex generators, one of which detects G2811A (R854Q) and G2823T (C858F), the other detects C2696T (R816W) and T2701A (H817Q). The allele frequency of the common G2811A (R854Q) mutation was investigated in the local (S. Wales) population by examination of 216 VWF genes (108 individuals) and was found to be 0.01. The heteroduplex-based test additionally detected a novel candidate type 2N mutation, C2810T (R854W) and a previously described polymorphism, G2805A (R852Q). The polymorphism showed allele frequencies of 0.92 (G nucleotide) and 0.08 (A nucleotide) in the population study.

Expression of Phosphate Transporters during Dental Mineralization

The importance of phosphate (Pi) as an essential component of hydroxyapatite crystals suggests a key role for membrane proteins controlling Pi uptake during mineralization in the tooth. To clarify the involvement of the currently known Pi transporters (Slc17a1, Slc34a1, Slc34a2, Slc34a3, Slc20a1, Slc20a2, and Xpr1) during tooth development and mineralization, we determined their spatiotemporal expression in murine tooth germs from embryonic day 14.5 to postnatal day 15 and in human dental samples from Nolla stages 6 to 9. Using real-time polymerase chain reaction, in situ hybridization, immunohistochemistry, and X-gal staining, we showed that the expression of Slc17a1, Slc34a1, and Slc34a3 in tooth germs from C57BL/6 mice were very low. In contrast, Slc34a2, Slc20a1, Slc20a2, and Xpr1 were highly expressed, mostly during the postnatal stages. The expression of Slc20a2 was 2- to 10-fold higher than the other transporters. Comparable results were obtained in human tooth germs. In mice, Slc34a2 and Slc20a1 were predominantly expressed in ameloblasts but not odontoblasts, while Slc20a2 was detected neither in ameloblasts nor in odontoblasts. Rather, Slc20a2 was highly expressed in the stratum intermedium and the subodontoblastic cell layer. Although Slc20a2 knockout mice did not show enamel defects, mutant mice showed a disrupted dentin mineralization, displaying unmerged calcospherites at the mineralization front. This latter phenotypical finding raises the possibility that Slc20a2 may play an indirect role in regulating the extracellular Pi availability for mineralizing cells rather than a direct role in mediating Pi transport through mineralizing plasma cell membranes. By documenting the spatiotemporal expression of Pi transporters in the tooth, our data support the possibility that the currently known Pi transporters may be dispensable for the initiation of dental mineralization and may rather be involved later during the tooth mineralization scheme.

Sclerostin Deficiency Promotes Reparative Dentinogenesis

In humans, the SOST gene encodes sclerostin, an inhibitor of bone growth and remodeling, which also negatively regulates the bone repair process. Sclerostin has also been implicated in tooth formation, but its potential role in pulp healing remains unknown. The aim of this study was to explore the role of sclerostin in reparative dentinogenesis using Sost knockout mice ( Sost^-/-). The pulps of the first maxillary molars were mechanically exposed in 3-mo-old Sost^-/- and wild-type (WT) mice ( n = 14 mice per group), capped with mineral trioxide aggregate cement, and the cavities were filled with a bonded composite resin. Reparative dentinogenesis was dynamically followed up by micro-computed tomography and characterized by histological analyses. Presurgical analysis revealed a significantly lower pulp volume in Sost^-/- mice compared with WT. At 30 and 49 d postsurgery, a large-forming reparative mineralized bridge, associated with osteopontin-positive mineralization foci, was observed in the Sost^-/- pulps, whereas a much smaller bridge was detected in WT. At the longer time points, the bridge, which was associated with dentin sialoprotein-positive cells, had expanded in both groups but remained significantly larger in Sost^-/- pulps. Sclerostin expression in the healing WT pulps was detected in the cells neighboring the forming dentin bridge. In vitro, mineralization induced by Sost^-/- dental pulp cells (DPCs) was also dramatically enhanced when compared with WT DPCs. These observations were associated with an increased Sost expression in WT cells. Taken together, our data show that sclerostin deficiency hastened reparative dentinogenesis after pulp injury, suggesting that the inhibition of sclerostin may constitute a promising therapeutic strategy for improving the healing of damaged pulps.

Expression of phosphate transporters in optimized cell culture models for dental cells biomineralization

Phosphate is a key component of dental mineral composition. The physiological role of membrane proteins of dental cells is suspected to be crucial for mineralization mechanisms. Contrary to published data related to calcium, data on regulation of phosphate flux through membrane of mineralizing cells are scarce. To address this lack of data, we studied the expression of six membranous phosphate transporters in two dental cell lines: a rat odontoblastic cell line (M2H4) and a mouse ameloblastic cell line (ALC) for which we optimized the mineralizing culture conditions.

Minimal intervention dentistry II: part 3. Management of non-cavitated (initial) occlusal caries lesions--non-invasive approaches through remineralisation and therapeutic sealants

Epidemiological data on dental caries show that prevention and treatment needs have evolved significantly over the past two decades. In younger patients the distribution of caries lesions is mainly found on the occlusal surfaces. The treatment approaches utilised by dentists must evolve to integrate preventive and treatment solutions tailored to the care needs, which are straightforward to implement in the dental office and whose effectiveness is underpinned by scientific evidence. This article aims to describe the principles of non-invasive management of non-cavitated (initial) occlusal caries lesions, based on evidence from recent studies published in the international literature.

Tooth dentin defects reflect genetic disorders affecting bone mineralization

Several genetic disorders affecting bone mineralization may manifest during dentin mineralization. Dentin and bone are similar in several aspects, especially pertaining to the composition of the extracellular matrix (ECM) which is secreted by well-differentiated odontoblasts and osteoblasts, respectively. However, unlike bone, dentin is not remodelled and is not involved in the regulation of calcium and phosphate metabolism. In contrast to bone, teeth are accessible tissues with the shedding of deciduous teeth and the extractions of premolars and third molars for orthodontic treatment. The feasibility of obtaining dentin makes this a good model to study biomineralization in physiological and pathological conditions. In this review, we focus on two genetic diseases that disrupt both bone and dentin mineralization. Hypophosphatemic rickets is related to abnormal secretory proteins involved in the ECM organization of both bone and dentin, as well as in the calcium and phosphate metabolism. Osteogenesis imperfecta affects proteins involved in the local organization of the ECM. In addition, dentin examination permits evaluation of the effects of the systemic treatment prescribed to hypophosphatemic patients during growth. In conclusion, dentin constitutes a valuable tool for better understanding of the pathological processes affecting biomineralization.

PHEX analysis in 118 pedigrees reveals new genetic clues in hypophosphatemic rickets

Familial hypophosphatemic rickets is a rare disease, which is mostly transmitted as an X-linked dominant trait, and mutations on the phosphate regulating gene with homologies to endopeptidases on the X-chromosome (PHEX) gene are responsible for the disease in most familial cases. In this study we analyzed PHEX in a large cohort of 118 pedigrees representing 56 familial cases and 62 sporadic cases. The high-resolution melting curves technique was tested as a screening method, along with classical sequencing. PHEX mutations have been found in 87% of familial cases but also in 72% of sporadic cases. Missense mutations were found in 16 probands, two of which being associated with other PHEX mutations resulting into truncated proteins. By plotting missense mutations described so far on a 3D model of PHEX we observed that these mutations focus on two regions located in the inner part of the PHEX protein. Family members of 13 sporadic cases were analyzed and a PHEX mutation was detected in one of the apparently healthy mother. These results highlight the major role of PHEX in X-linked dominant hypophosphatemic rickets, and give new clues regarding the genetic analysis of the disease. A screening of the different family members should be mandatory when a PHEX mutation is assessed in a sporadic case and the search for another PHEX mutation should be systematically proceed when facing a missense mutation.

Vitamin D receptor genotype in hypophosphatemic rickets as a predictor of growth and response to treatment

CONTEXT

Treatment of X-linked hypophosphatemic rickets improves bone mineralization and bone deformities, but its effect on skeletal growth is highly variable.

OBJECTIVE

Genetic variants in the promoter region of the vitamin D receptor (VDR) gene may explain the response to treatment because this receptor mediates vitamin D action.

DESIGN

We studied the VDR promoter haplotype structure in a large cohort of 91 patients with hypophosphatemic rickets including 62 patients receiving 1alpha-hydroxyvitamin D3 derivatives and phosphates from early childhood on.

RESULTS

Treatment improved bone deformities and final height, but 39% of treated patients still had short stature at the end of growth (-2 sd score or below). Height was closely associated with VDR promoter Hap1 genotype. Hap1(-) patients (35% of the cohort) had severe growth defects. This disadvantageous association of Hap1(-) status with height was visible before treatment, under treatment, and on to adulthood. Gender and age at initiation of treatment could not account for the Hap1 effect. No association with growth was found with a polymorphism of the PTH receptor gene otherwise found to be associated with adult height. Compared with Hap1(+) patients, those who were Hap1(-) had a higher urinary calcium response to 1alpha-hydroxyvitamin D3 and had significantly lower circulating FGF23 levels (C-terminal assay), taking into account their phosphate and 1alpha-hydroxyvitamin D3 intakes.

CONCLUSIONS

The present work identifies the VDR promoter genotype as a key predictor of growth under treatment with 1alpha-hydroxyvitamin D3 derivatives in patients with hypophosphatemic rickets, including those with established PHEX alterations. The VDR promoter genotype appears to provide valuable information for adjusting treatment and for deciding upon the utility of early GH therapy.

Dentin noncollagenous matrix proteins in familial hypophosphatemic rickets

Familial hypophosphatemic rickets is transmitted in most cases as an X-linked dominant trait and results from the mutation of the PHEX gene predominantly expressed in osteoblast and odontoblast. Patients with rickets have been reported to display important dentin defects. Our purpose was to explore the structure, composition and distribution of noncollagenous proteins (NCPs) of hypophosphatemic dentin. We collected teeth from 10 hypophosphatemic patients whose mineralization occurred either in a hypophosphatemic environment or in a corrected phosphate and vitamin environment. Teeth were examined by scanning electron microscopy, immunohistochemistry and Western blot analysis. An abnormal distribution (accumulation in interglobular spaces) and cleavage of the NCPs and particularly of matrix extracellular phosphoglycoprotein were observed in deciduous dentin. In contrast, it was close to normal in permanent dentin mineralized under corrected conditions. In conclusion, dentin mineralization in a corrected phosphate and vitamin D environment compensates the adverse effect of PHEX mutation.

Review: behaviour of endothelial cells faced with hypoxia

Hypoxia is a diminution of oxygen quantity delivered to tissue for cellular need to product energy. Hypoxia derives from two major conditions in health diseases: anemia and ischemia. Anemic hypoxia comes from damage to O(2) transport like red blood cells diminution or disease. Ischemic hypoxia is a diminution of blood flow following a diminution of blood volume after a hemorrhagic shock. After hypoxia, vessels dilate to increase blood flow allowing a better oxygenation of peripheral tissues. This vasodilation appears immediately after the beginning of hypoxia and can be maintained during several hours. Today, the molecular mechanisms of this vasodilation stay unclear. But it seems that potassic channels, ATP concentration and medium acidification in addition to vasodilator/vasoconstrictor balance play a great role to facilitate the oxygenation of the ischemic areas.As endothelial cells (EC) are lining the vasculature, they are always in contact with blood, which carries, amongst other compounds, oxygen. In this way, they are the first target for an oxygen partial pressure (PO(2)) diminution. EC, through different mechanosensors, can sense a variation in PO(2) and adapt their metabolism to maintain ATP production. Under hypoxia, EC switch into hypoxic metabolism, leading to the production of reactive oxygen species (ROS). Indeed, when PO(2) is low, the respiratory chain in the mitochondria runs slower. Furthermore, cytochrome C capacity to trap O(2) is reduced; this phenomenon alters the cellular redox potential and leads to the accumulation of electrons that induce the formation of ROS.This review presents an overview of the behaviour of endothelial cells face to hypoxia. We propose to focus on nitric oxide, hypoxia inducible factor (HIF), lactate and ROS productions. Then we present the different mode of culture of EC under hypoxia. Finally, we conclude on the difficulty to study hypoxia because of the various types of system developed to reproduce this phenomenon and the different signalling ways that can be activated.

In vitro impact of physiological shear stress on endothelial cells gene expression profile

In the vascular system, the shear applied to the vascular wall activates mechano-sensors located on endothelial cells (ECs) leading to a modification in the gene expression profile. We applied laminar shear stress at 1 Pa on ECs for 6 h and measured by quantitative real time PCR the expression modulation of genes implied in inflammation (ICAM-1 and E-selectin), oxidative stress sensing (HO-1) and vascular tone modulation (eNOS). We showed that all these genes are shear stress inducible. ICAM-1 is more up-regulated than E-selectin suggesting different levels of implication in inflammatory responses and different modes of induction (SSRE, cytokine). Laminar shear stress induces an oxidative stress translated into HO-1 up-regulation, and a possible vasodilatation through the induction of eNOS. Our laminar shear stress system opens a novel and interesting frame in the evaluation of the impact on ECs and blood cells of new pharmacological substances injected in the bloodstream.

Type 2M vWD resulting from a lysine deletion within a four lysine residue repeat in the A1 loop of von Willebrand factor

Type 1 von Willebrand disease is characterized by a decreased plasma concentration of functionally normal von Willebrand factor (vWF) whereas type 2M is characterised by an abnormal vWF displaying decreased affinity for platelets. In these two types of patients, the multimeric structure of vWF is normal. We report here the identification, in two unrelated families from the UK and Algeria, of an in-frame 3 bp deletion, at the heterozygous state, resulting in the deletion of a lysine residue within a four lysine repeat at position 642-645 of the mature vWF subunit (del K 1405-1408 in pre-pro vWF). The patients who have a discrepancy between vWF antigen level and vWF ristocetin cofactor activity exhibited decreased ristocetin-induced binding but only a slight decrease in the percentage of high molecular weight (HMW) multimers in plasma. Recombinant vWF harbouring this deletion did not bind to platelet GPIb in the presence of ristocetin or botrocetin although the protein is multimerized. Consequently, this lysine deletion was considered as a type 2M vWD mutation.

Conformational changes in the D' domain of von Willebrand factor induced by CYS 25 and CYS 95 mutations lead to factor VIII binding defect and multimeric impairment

We report 2 new mutations identified in 3 patients and characterized by the markedly decreased affinity of von Willebrand factor (vWF) for factor VIII (FVIII). Patients 2 and 3, who have a typical type 2N phenotype, were found to be compound heterozygous for Arg91Gln and Cys25Tyr or Cys95Phe, respectively. Patient 1, who is the first cousin of patient 2, had an FVIII binding defect of vWF, low levels of vWF, and multimeric impairment. She was found to be compound heterozygous for the mutations Cys25Tyr and a stop codon (D93ter) in exon 4. Transient expression of recombinant vWF (rvWF) containing either Cys25Tyr or Cys95Phe mutations resulted in mutated rvWF with markedly reduced FVIII binding ability, multimeric structure impairment, and a significant decrease in the vWF expression level. Moreover, the use of anti-vWF monoclonal antibodies that inhibit the FVIII binding showed that these 2 mutations likely induce a conformational change in the D' domain. These results show that the native conformation of the D' domain of vWF is not only required for FVIII binding but also for normal multimerization and optimal secretion.

Association between high von willebrand factor levels and the Thr789Ala vWF gene polymorphism but not with nephropathy in type I diabetes. The GENEDIAB Study Group and the DESIR Study Group

BACKGROUND

A genetic susceptibility for diabetic kidney disease is suspected since diabetic nephropathy occurs in only 30 to 40% of type I diabetic patients. As elevated von Willebrand factor (vWF) plasma concentrations have been reported to precede the development of microalbuminuria in type I diabetes, we addressed a possible implication of vWF as a genetic determinant for diabetic nephropathy.

METHODS

Three known vWF gene polymorphisms were genotyped in a group of 493 type I diabetic subjects, all showing proliferative retinopathy, but with various stages of renal involvement, which ranged from no microalbuminuria, despite a mean duration of diabetes of 31 years, to advanced nephropathy (GENEDIAB Study): Thr789Ala (Rsa I), M-/M+ (Msp I) (intron 19), and Ala1381Thr (Hph I). Plasma vWF and factor VIII (F VIII) levels were also measured in this population.

RESULTS

Plasma vWF and F VIII levels were increased in diabetic subjects with nephropathy (P < 0.001) or with coronary heart disease (CHD; P < 0.001), but there was no interaction of both conditions on plasma levels. The Msp I polymorphism (M-/M+) was weakly associated with nephropathy (P = 0. 04), but this association was not more significant when other risk factors were used in a logistic regression analysis. The vWF Thr789Ala polymorphism was associated with CHD (P = 0.002) and with plasma vWF levels. Logistic regression analysis indicated an independent and codominant effect of the Thr789Ala polymorphism on CHD, but not on nephropathy, with a maximal risk for Ala/Ala homozygotes (OR = 4.2, 95% CI, 1.8 to 9.9, P = 0.0008).

CONCLUSION

It is unlikely that polymorphisms in the vWF gene contribute to the risk for nephropathy in type I diabetic patients. However, the Thr789Ala polymorphism might affect the risk for CHD in this population through modulation of plasma vWF levels.

A novel mutation in the D3 domain of von Willebrand factor markedly decreases its ability to bind factor VIII and affects its multimerization

In type 2N von Willebrand disease (vWD), von Willebrand factor (vWF) is characterized by normal multimeric pattern, normal platelet-dependent function, but a markedly decreased affinity for factor VIII (FVIII). In this report, we describe the case of a vWD patient who has an abnormal vWF multimers distribution associated with a markedly decreased vWF ability to bind FVIII. Sequencing analysis of patient's vWF gene showed, at heterozygous state, a G-->A transition resulting in the substitution of Asn for Asp at position 116 of the mature vWF subunit and a C-->T transition, changing the codon for Arg 896 into a stop codon. His sister who has a subnormal vWF level, but a normal FVIII/vWF interaction, was found to be heterozygous for the Arg896ter mutation only. Recombinant vWF (rvWF) containing the candidate (Asn116) missense mutation was expressed in COS-7 cells. The expression level of Asn116rvWF was significantly decreased compared with wild-type rvWF. The multimeric pattern of Asn116rvWF was greatly impaired as shown by the decrease in high molecular weight forms. The FVIII binding ability of Asn116rvWF was dramatically decreased. These data show that the Asp116Asn substitution is the cause of both the defective FVIII/vWF interaction and the impaired multimeric pattern observed in the patient's vWF. The monoclonal antibody 31H3 against D' domain of vWF (epitope aa 66-76) that partially inhibits the FVIII binding and recognizes only nonreduced vWF, showed a decreased ability to bind Asn116rvWF when used as capture-antibody in enzyme-linked immunosorbent assay (ELISA). This result suggests that a potential conformation change in the D' domain is induced by the Asp116Asn substitution, which is localized in the D3 domain.

Identification of new type 2B von Willebrand disease mutations: Arg543Gln, Arg545Pro and Arg578Leu

We report the identification in five patients (three families) affected with type 2B von Willebrand disease (VWD) of three heterozygous nucleotide substitutions at the codon for arginine 543, 545 and 578 of the mature von Willebrand factor (VWF) subunit resulting in a glutamine, proline and leucine substitution, respectively. These mutations are located in the A1 loop where prevalent type 2B mutations (Arg543Trp, Arg545Cys and Arg578Gln) have been already identified at the same positions. By in vitro mutagenesis of full-length cDNA of VWF and transient expression in Cos-7 cells, we have shown that the six corresponding mutated recombinant VWFs (Gln543, Trp543, Cys545, Pro545, Leu578 and Gln578 rVWF) exhibited quantitatively normal expression and normal multimeric pattern but increased ristocetin- and botrocetin-induced binding to platelets as compared with that for wild-type rVWF. The two mutations at position 545 induced the greatest reactivity for GPIb of corresponding rVWFs as compared to the two mutations at positions 543 and 578.

Type 2N von Willebrand disease due to Arg91Gln substitution and a cytosine deletion in exon 18 of the von Willebrand factor gene

Two members of a family previously classified as type 1 von Willebrand disease (VWD), showed a quantitative defect in von Willebrand factor (VWF) antigen and ristocetin cofactor activity and an abnormal capacity of VWF to bind FVIII. Sequencing of the VWF gene region coding for the FVIII binding domain revealed the most frequent type 2N mutation: a single nucleotide change (G2811A) in exon 20, resulting in substitution of glutamine (Gln) for arginine (Arg) 91 in the mature VWF protein in one allele. The other allele contained a cytosine deletion (2680delC) in exon 18, introducing a premature stop codon at position 79 (Val79X) which produced a quantitative defect in VWF levels. The Arg91Gln defect is usually not evident in heterozygotes; however, in these patients it was expressed due to the lack of VWF production from the other allele. This is the first report of type 2N VWD in Italy.

A new candidate mutation (N528S) within the von Willebrand factor propeptide identified in a Japanese patient with phenotype IIC of von Willebrand disease

Phenotype IIC of von Willebrand disease (vWD) is a subtype of type 2A vWD characterized by recessive inheritance and an impaired multimerization of von Willebrand factor (vWF) molecules beyond dimers. The 5 patients with phenotype IIC whose vWF gene defect has been characterized so far are either homozygous or double heterozygotes for mutations localized in exons 11, 12, 14 or 15. We report here the identification of a new candidate mutation in a previously described Japanese patient affected with phenotype IIC vWD. The propositus is homozygous for the A1833G nucleotide substitution, in exon 14 of vWF gene, responsible for the N528S mutation within the vWF propeptide. This finding is in agreement with the consanguineous origin of the propositus, whose parents are first cousins. Six patients' relatives who are asymptomatic were studied and found heterozygous for the N528S mutation. The screening of the whole vWF gene, either by SSCP or sequencing, did not reveal any other deleterious sequence alteration in the patient. Furthermore, the N528S nonconservative substitution identified is located in the vWF propeptide region, where the other phenotype IIC mutations described so far are clustered. The N528S candidate mutation characterized is, therefore, most probably responsible for the multimerization defect of vWF observed in this patient.

Type 2N von Willebrand disease: rapid genetic diagnosis of G2811A (R854Q), C2696T (R816W), T2701A (H817Q) and G2823T (C858F)--detection of a novel candidate type 2N mutation: C2810T (R854W)

The majority of patients with type 2N von Willebrand disease (VWD type 2N) have mutations in the region of the von Willebrand factor (VWF) gene encoding the factor VIII binding domain of VWF. Two mutations predominate among VWD type 2N patients: G2811A and C2696T, which respectively bring about the amino acid substitutions R854Q and R816W in VWF. Several other mutations have been found in VWD type 2N, including T2701A (H817Q) and G2823T (C858F). We have developed a genetic test which permits rapid screening for these four mutations in a single polymerase chain reaction (PCR). The test employs induced heteroduplex formation using two universal heteroduplex generators, one of which detects G2811A (R854Q) and G2823T (C858F), the other detects C2696T (R816W) and T2701A (H817Q). The allele frequency of the common G2811A (R854Q) mutation was investigated in the local (S. Wales) population by examination of 216 VWF genes (108 individuals) and was found to be 0.01. The heteroduplex-based test additionally detected a novel candidate type 2N mutation, C2810T (R854W) and a previously described polymorphism, G2805A (R852Q). The polymorphism showed allele frequencies of 0.92 (G nucleotide) and 0.08 (A nucleotide) in the population study.

Molecular genetics of von Willebrand disease

Von Willebrand disease (vWD), the most common congenital bleeding disorder in man, is related to quantitative and/or qualitative abnormalities of von Willebrand factor (vWF). This multimeric glycoprotein serves as carrier protein of factor VIII, an essential cofactor of coagulation in plasma, and promotes platelet adhesion to the damaged vessel and platelet aggregation. Distinct abnormalities of vWF are responsible for the three types of vWD. Types 1 and 3 are characterized by a quantitative defect of vWF whereas type 2, comprising subtypes 2A, 2B, 2M and 2N, refers to molecular variants with a qualitative defect of vWF. The knowledge of the structure of the vWF gene and the use of Polymerase Chain Reaction (PCR) have led to the identification of the molecular basis of vWD in a significant number of patients. Type 2A is characterized by a decreased platelet-dependent function of vWF associated with the absence of high molecular weight (HMW) multimers of vWF. Most of the type 2A mutations have been identified in the A2 domain of vWF which contains a proteolytic site, while a few others have been found within the propeptide and the C-terminal part of vWF which are involved in its multimerization and dimerization, respectively. In type 2B, defined by an increased affinity of vWF to platelet glycoprotein Ib (GPIb), various amino-acid (aa) substitutions or insertion have been localized within the A1 domain containing the GPIb binding site. In the latter domain have been also identified the few molecular abnormalities described in type 2M which is defined by a decreased platelet-dependent function not caused by the absence of HMW multimers. In type 2N, characterized by a defective binding of vWF to factor VIII, several aa substitutions have been identified within the factor VIII-binding domain in the N-terminal part of vWF. The identification of gene defects remains difficult in types 1 and 3. Whereas various abnormalities (total, partial or point deletions, point insertions, nonsense mutations) have already been identified in type 3, the molecular basis of type 1 is still unresolved in most cases. The characterization of the molecular basis of vWD is of fundamental interest in providing further insight into the structure-function relationship and the biosynthesis of vWF.

Gene defects in 150 unrelated French cases with type 2 von Willebrand disease: from the patient to the gene. INSERM Network on Molecular Abnormalities in von Willebrand Disease

Type 2 vWD is defined by qualitative defects of vWF and is subdivided into four subtypes: 2N, 2B, 2A and 2M. The characterization of 150 unrelated French cases with type 2 vWD emphasizes the heterogeneity of this group. In 51 cases of type 2N vWD, new mutations were found not only in the D' domain (Cys25Tyr and Cys95Phe) but also in the D3 domain (Asp116Asn and Cys297Arg). In 42 cases of type 2B vWD, no new mutation was detected. In 45 cases with type 2A phenotype, three new candidate mutations were found in the A2 domain: Gln793Arg, Val841Phe and Leu876Pro. In addition, four new candidate mutations were detected in the A1 domain: Cys509Gly, Arg545His, Arg552Cys and Cys695Tyr. Finally, five new candidate mutations were identified in 12 patients with 2M (or unclassified) phenotype: Leu513Pro, Gly561A1a, Glu596Lys, Arg611Leu and IIe662Phe. For all candidate mutations, expression studies are in progress. This study of a large number of French variants of vWD brings further insight into the relationship between phenotype and genotype.

Rapid mutation screening in type 2A von Willebrand's disease using universal heteroduplex generators

Patients with type 2A von Willebrand's disease (VWD) commonly have missense mutations in the A2 domain of the von Willebrand factor (VWF) protein. This domain is encoded by the 3' region of VWF gene exon 2 8 and the large majority of patients have heterozygous mutations clustered in the sequence between codons 742 and 909. We describe a DNA-based diagnostic technique which enables at least 10 previously described mutations to be rapidly identified. The method involves polymerase chain reaction (PCR) amplification of two exon 28 gene segments between codons 717-788 and 803-893, respectively. Each fragment is then hybridized with a synthetic complementary DNA molecule of similar size, termed a Universal Heteroduplex Generator (UHG). The UHG contains base deletions contiguous to the sites of known mutations and, following hybridization, allele-specific heteroduplexes are generated which can be detected by simple polyacrylamide gel electrophoresis and ethidium bromide staining. A small panel of UHG molecules covering the 3' region of exon 28 should enable the large majority of type 2A VWD patients to be rapidly diagnosed by genotype.

Combined hereditary disorders of haemophilia B Leyden (-6 G-->A) and type 1 von Willebrand disease

Multiple coagulation disorders are unusual. We report here a combination of haemophilia B Leyden with type 1 von Willebrand disease (vWD) affecting different members of the same family. Haemophilia B Leyden was due to a -6 G-->A mutation within the promoter of the factor IX gene and was responsible for a mild haemophilia in the father of the proband. The proband and her sister (age 4 and 6) exhibited a twofold lower level of factor IX activity (0.4 IU/ml) than the paternal grandmother (0.95 IU/ml). The differences in F IX levels in the three carriers of the same -6 G-->A mutation suggest the implication of an age-related mechanism responsible for the increase in factor IX plasma level. Haemophilia B Leyden patient and carriers suffered also from a mild von Willebrand disease. The diagnosis of this associated type 1 vWD was performed by assaying plasma von Willebrand factor together with multimer electrophoretic studies and DDAVP test. The inheritance of this vWD was investigated by haplotype analysis of the vWF gene. Individuals affected by such an association are actually asymptomatic, but per- and post-operative bleeding risk remains to be evaluated.

Effects of different amino-acid substitutions in the leucine 694-proline 708 segment of recombinant von Willebrand factor

Type 2B von Willebrand disease (vWD) is characterized by an increased affinity of von Willebrand factor (vWF) for binding to platelet glycoprotein Ib (GpIb). Most type 2B candidate mutations are clustered in the 509-695 disulphide loop but three of them (H505D, L697V and A698V) are outside this loop. We confirm here that the A698V mutation is a type 2B mutation by its expression in Cos-7 cells. As the L697V and A698V type 2B mutations both induce the presence of a valine residue in the 694-708 sequence, we created and expressed different mutated recombinant vWFs (rvWFs), in substituting the other leucine and alanine residues of this sequence (at positions 694, 701 and 706) into valine resides. V694rvWF and V706rvWF displayed decreased ristocetin-induced GpIb binding showing that it is not always the presence of a valine residue that may explain the increased affinity of type 2B vWF for GpIb. We also compared the interaction with platelets of V697rvWF and V698rvWF to those obtained with rvWFs reproducing two prevalent type 2B mutations located in the loop (R543W and V553M). We show that the two mutations located in the loop are more reactive than the two mutations identified outside the loop.

Factor VIII gene inversions in severe hemophilia A: results of an international consortium study

Twenty-two molecular diagnostic laboratories from 14 countries participated in a consortium study to estimate the impact of Factor VIII gene inversions in severe hemophilia A. A total of 2,093 patients with severe hemophilia A were studied; of those, 740 (35%) had a type 1 (distal) factor VIII inversion, and 140 (7%) showed a type 2 (proximal) inversion. In 25 cases, the molecular analysis showed additional abnormal or polymorphic patterns. Ninety-eight percent of 532 mothers of patients with inversions were carriers of the abnormal factor VIII gene; when only mothers of nonfamilial cases were studied, 9 de novo inversions in maternal germ cells were observed among 225 cases (approximately 1 de novo maternal origin of the inversion in 25 mothers of sporadic cases). When the maternal grandparental origin was examined, the inversions occurred de novo in male germ cells in 69 cases and female germ cells in 1 case. The presence of factor VIII inversions is not a major predisposing factor for the development of factor VIII inhibitors; however, slightly more patients with severe hemophilia A and factor VIII inversions develop inhibitors (130 of 642 [20%]) than patients with severe hemophilia A without inversions (131 of 821 [16%]).

Identification of two mutations (Arg611Cys and Arg611His) in the A1 loop of von Willebrand factor (vWF) responsible for type 2 von Willebrand disease with decreased platelet-dependent function of vWF

We report the identification of von Willebrand factor (vWF) gene mutations within exon 28 occurring in three unrelated families with an infrequent form of type 2 von Willebrand disease (vWD). A C-->T transition and a G-->A transition, both at the codon for arginine 611 of the mature vWF subunit, were found. They result in either a cysteine or an histidine substitution, respectively. Patients were found to be heterozygous for these substitutions and the vWD was transmitted dominantly. These substitutions have been reproduced by in vitro mutagenesis of full-length cDNA of vWF and transiently expressed in Cos-7 cells. The corresponding recombinant vWFs (rvWF) exhibited decreased expression and a significant decrease in the high molecular weight multimeric forms. In addition, ristocetin- and botrocetin-induced binding of mutated rvWFs to platelets were markedly decreased as compared with that for the wild-type rvWFs. Thus, the structural and functional characterization of both mutated rvWFs confirmed that the two nucleotide substitutions identified at position 611 of the mature subunit of vWF are real mutations. Although they are located in the A1 loop containing most of the type 2B mutations inducing increased affinity of vWF for platelet glycoprotein Ib, they are responsible for abnormal vWF with decreased platelet-dependent function.

New variant of type II von Willebrand's disease with structural abnormality of plasma von Willebrand factor in a patient with very mild bleeding history

A new variant of von Willebrand's disease has been discovered in 2 members of a Macedonian family of 6. The proband, an 8-year-old boy, showed a prolonged bleeding episode on 1 occasion. Ristocetin-induced platelet aggregation and bleeding time were normal. In plasma, ristocetin cofactor activity (RCo) and von Willebrand factor (vWf) antigen were reduced to the same clearly low level. The determination of vWf antigen of platelets resulted in borderline values, while RCo was clearly reduced. Low- and intermediate-resolution agarose gel electrophoresis showed absence of the largest multimers in plasma vWf, and slight reduction in platelet vWf. High-resolution gels revealed abnormal multimeric structure only in plasma vWf. The smaller multimers could be resolved in a broad central band flanked by 4 fainter satellite bands; however, satellite bands close to the central band were more intense, and more distant ones were fainter, compared to normal plasma. The central band of the fastest-moving multimer was markedly intensified, and the mobility of the whole quintuplet was slightly reduced. Heredity seems to be autosomal-dominant. No mutation was found in exon 28 of the vWf gene. Because there was only 1 mild bleeding episode in the family, this structural variation seems to have only little clinical consequence. We conclude that this vWf abnormality is different from those observed in other type II variants previously described. Based on the revised classification by the International Society on Thrombosis and Haemostasis, we proposed designation type 2A-Bern for this new subtype.

Diagnosis of subtype 2B von Willebrand disease in a patient with 2A phenotype of plasma von Willebrand factor

Type 2A of von Willebrand disease refers to qualitative variants with decreased platelet dependent function that is associated with the absence of high molecular weight forms of von Willebrand factor (vWF) multimers. Type 2B refers to qualitative variants with increased affinity for platelet glycoprotein Ib. In this report we describe the study of a patient who has been previously diagnosed as having subtype 2A von Willebrand disease (vWD), because she had no heightened ristocetin-induced platelet aggregation, no large and intermediate molecular weight von Willebrand factor (vWF) multimers in plasma, and no increase in plasma vWF capacity to bind to normal platelets in the presence of low ristocetin concentrations. The DNA sequencing of the 3' part of the exon 28 of the vWF gene where most of the subtype 2A mutations have already been identified, did not detect any nucleotide change. At variance, a G to A transition changing the encoded amino acid residue from Val 553 to Met in mature vWF, was found in the 5' part of this exon. This mutation which has already been found in several unrelated families with 2B vWD and the increased binding of the patient platelet vWF on normal platelets in the presence of low ristocetin concentrations provide evidence for subtype 2B vWD. This study thus illustrates the importance of the molecular characterization of patients in the correct diagnosis and classification of type 2 vWD.

Biological effect of desmopressin in eight patients with type 2N ('Normandy') von Willebrand disease. Collaborative Group

It is generally thought that the plasma increase in factor VIII (FVIII) after desmopressin (dDAVP) infusion is related to the plasma increase in von Willebrand factor (vWF), which is the plasma carrier for FVIII. The aim of this study was to evaluate the FVIII and vWF responses in patients with type 2N vWD, characterized by the mild FVIII deficiency related to markedly decreased affinity of vWF for FVIII. At different times after one intravenous dose of dDAVP (0.3 or 0.4 microgram/kg) we measured the FVIII coagulant activity, FVIII antigen, vWF antigen and ristocetin cofactor activity, in eight patients with either Arg91Gln or Arg53Trp amino acid substitution in mature vWF. In all the patients, whatever their mutation, the dDAVP infusion resulted in a 2.3 +/- 0.7-fold increase of vWF and a variable rise (9.5 +/- 7.7 times) of FVIII, whereas the vWF capacity to bind FVIII was not improved. The FVIII response was more transient than vWF response, and FVIII half disappearance time was evaluated to be approximately 3 h. The data indicate that the stabilizing effect of vWF on FVIII is not responsible for the FVIII increase induced by dDAVP. The clinical implication of this study is that, in the 2N vWD patients, dDAVP may be a useful prophylactic or curative treatment when the test dose has been shown to be effective to reach a haemostatic FVIII level.

Characterization of von Willebrand factor gene defects in two unrelated patients with type IIC von Willebrand disease

Genetic studies were performed in two unrelated patients with the IIC phenotype of von Willebrand disease (vWD) characterized by the increased concentration of the protomeric form of von Willebrand factor (vWF). In patient B, the sequencing of both exons 15 and 16 of the vWF gene showed two sequence alterations: a 3-bp insertion in exon 15 resulting in the insertion of a Glycine at position 625 (625insGly) and a 2-bp deletion in exon 16 leading to a premature translational stop at codon 711 (711 ter), at the heterozygote state. Patient A was found homozygous for a single point mutation also localized in exon 15 and responsible for the substitution Cys623Trp. These candidate mutations were not found in a panel of 96 normal chromosomes, suggesting a causal relationship with IIC vWD phenotypic expression. The composite heterozygote or homozygote state of both patients supports the recessive mode of inheritance already described for this phenotype. Furthermore, the localization of these gene defects in the D2 domain of vWF propeptide, known to play an important role in vWF multimerization, provides another argument in favor of their causative effect regarding the peculiar multimeric pattern of vWF in these patients.

Fine epitope mapping of monoclonal antibodies to the NH2-terminal part of von Willebrand factor (vWF) by using recombinant and synthetic peptides: interest for the localization of the factor VIII binding domain

Two different approaches were used in order to define the epitope of three monoclonal antibodies (MoAbs) against the NH2-terminal part of the mature subunit of von Willebrand factor (vWF) which contains its factor VIII (FVIII) binding site. First, a vWF cDNA fragment library using the bacteriophage lambda gt11 expression vector was screened with radiolabelled MoAbs. The epitope of each MoAb was defined, following sequence analysis, by the overlapping DNA sequence of immunoreactive clones. MoAb 32B12, a potent inhibitor of FVIII/vWF interaction, binds within the Glu35-Ile81 sequence of vWF subunit. MoAb 14A12, a non-inhibitory antibody, recognizes a sequence within Thr141-Val220. MoAb 31H3, a partial inhibitory antibody, gives no positive clone. In the second method, a panel of 24 synthetic pentadecapeptides corresponding to the first NH2-terminal 105 amino acid residues was used to block the binding of inhibitor MoAbs to immobilized vWF in an ELISA system. The localization of MoAb 32B12 epitope was confirmed and restricted to the Met51-Ala60 sequence. The MoAb 31H3 binding to vWF is inhibited by two synthetic peptides with the overlapping sequence Cys66-Gly76. All these data confirm that the FVIII binding site of vWF is not limited to the binding area (Thr78-Thr96) of the previously described MoAbs inhibiting FVIII/vWF interaction but is composed of several key sequences.

Leu 697-->Val mutation in mature von Willebrand factor is responsible for type IIB von Willebrand disease

Type IIB von Willebrand disease is characterized by the selective loss of high molecular weight von Willebrand factor (vWF) multimers from plasma and enhanced platelet agglutination of platelet-rich-plasma in the presence of low concentrations of ristocetin. We identified, in two related patients, a C-->G transversion resulting in the substitution of Valine for Leucine at position 697 of the mature subunit of vWF. We reproduced this mutation in vWF cDNA and expressed the recombinant protein in Cos-7 cells. The subunit composition and multimeric structure of mutated protein (rvWFLeu697Val) were similar to the wild-type recombinant (WTrvWF). Ristocetin-induced binding of rvWFLeu697Val to platelets was markedly increased in the presence of low doses of ristocetin and slightly increased with botrocetin as compared with that for WTrvWF, whereas collagen binding was not affected by the mutation. These data show that the Leu 697-->Val substitution is not a rare polymorphism but is responsible for the subtype IIB characteristic abnormalities identified in the two affected patients; however, it is not located in the area of vWF (amino acid 540 to amino acid 578) where most of the other type IIB mutations have already been reported.

Substitution of cysteine for phenylalanine 751 in mature von Willebrand factor is a novel candidate mutation in a family with type IIA von Willebrand disease

Type IIA is a variant form of von Willebrand disease (vWD) characterized by the absence of von Willebrand factor (vWF) high molecular weight multimers in plasma. Most of the candidate missense mutations potentially responsible for type IIA vWD have been found clustered within a short segment of vWF, lying between Gly742 and Glu875 of the mature subunit. The present work reports a single heterozygous T-->G transversion in eight patients from a large type IIA vWD family, resulting in the substitution Phe751-->Cys. The absence of this mutation in 100 normal vWF genes as well as the lack, in these patients, of any other abnormality within the whole exon 28 encoding amino acids 463-921 of mature vWF, provide a strong support that this non-conservative mutation may be at the origin of the disease in this family. The presence of an additional cysteine at position 751 may induce a conformational change of the vWF subunit affecting either its 'in vivo' sensitivity to proteolytic cleavage or, more likely, its intracellular transport as suggested by the abnormal multimeric pattern of platelet vWF observed in these patients.