Rapid genotype analysis in type 2B von Willebrand's disease using a universal heteroduplex generator

The heparin binding domain of von Willebrand factor binds to growth factors and promotes angiogenesis in wound healing

During wound healing, the distribution, availability, and signaling of growth factors (GFs) are orchestrated by their binding to extracellular matrix components in the wound microenvironment. Extracellular matrix proteins have been shown to modulate angiogenesis and promote wound healing through GF binding. The hemostatic protein von Willebrand factor (VWF) released by endothelial cells (ECs) in plasma and in the subendothelial matrix has been shown to regulate angiogenesis; this function is relevant to patients in whom VWF deficiency or dysfunction is associated with vascular malformations. Here, we show that VWF deficiency in mice causes delayed wound healing accompanied by decreased angiogenesis and decreased amounts of angiogenic GFs in the wound. We show that in vitro VWF binds to several GFs, including vascular endothelial growth factor-A (VEGF-A) isoforms and platelet-derived growth factor-BB (PDGF-BB), mainly through the heparin-binding domain (HBD) within the VWF A1 domain. VWF also binds to VEGF-A and fibroblast growth factor-2 (FGF-2) in human plasma and colocalizes with VEGF-A in ECs. Incorporation of the VWF A1 HBD into fibrin matrices enables sequestration and slow release of incorporated GFs. In vivo, VWF A1 HBD-functionalized fibrin matrices increased angiogenesis and GF retention in VWF-deficient mice. Treatment of chronic skin wounds in diabetic mice with VEGF-A165 and PDGF-BB incorporated within VWF A1 HBD-functionalized fibrin matrices accelerated wound healing, with increased angiogenesis and smooth muscle cell proliferation. Therefore, the VWF A1 HBD can function as a GF reservoir, leading to effective angiogenesis and tissue regeneration.

A single, multiplex analysis for all relevant activating NRAS gene mutations using heteroduplex generators

We describe a multiplex polymerase chain reaction (PCR)-based test that detected all relevant NRAS activating mutations using a single PCR followed directly by electrophoresis. The test uses a Universal Heteroduplex Generator (UHG) to detect exon-2 (codon 61) NRAS mutations in multiplex with an UHG for exon-1 (codons 12 and 13). The method differentiated all 19 relevant mutations in these exons and showed a mutation independent sensitivity of approximately 6%. The sensitive, specific detection of all NRAS activating mutations using this single rapid test represents a minimum workload and could be applied readily for large-scale screening and for routine analysis.

Rapid detection of exon 1 NRAS gene mutations using universal heteroduplex generator technology

Specific NRAS oncogene missense mutations have been frequently found in some tumors and several hematological diseases, especially in those of myeloid origin. There is a wide range of PCR-based methods for screening and detection of NRAS exon 1 single-base substitutions. However, there are disadvantages and ambiguities associated with these techniques because all of them require either separate probes, separate PCR amplifications, or complicated post-PCR manipulations. This report describes a new approach for detection of NRAS gene mutations at codon 12 and 13 based on the DNA heteroduplex analysis method. The strategy relies upon differential electrophoretic behavior of induced heteroduplex molecules formed by cross-hybridization of two PCR-amplified species, the sample under analysis and the synthetic universal heteroduplex generator (UHG). The screening of a panel of all codon 12 and 13 NRAS mutant DNA variants indicated that this approach discriminates all 12 relevant mutations. The sensitivity of the method was estimated by a competitive assay where mutant alleles could be detected at a dilution level of 1 to 16 wild-type alleles. This UHG technology was tested on some clinical samples previously studied by PCR-ASO. This methodology is highly specific, sensitive, and achieves an appreciable reduction in workload and time because it requires one PCR amplification followed by polyacrylamide gel electrophoresis in standard conditions. We propose that this new approach may be applied as an alternative strategy for codon 12-13 NRAS mutations and it could be easily incorporated into the range of routine assays performed in oncology laboratories.

Molecular genetics of type 2 von Willebrand disease

Type 2 von Willebrand disease (VWD) is characterized by a wide heterogeneity of functional and structural defects. These abnormalities' cause either defective von Willebrand factor (VWF)-dependent platelet function in subtypes 2A, 2B, and 2M or defective VWF-factor VIII (FVIII) binding in subtype 2N. The diagnoses of types 2A, 2B, and 2M VWD may be guided by the observation of disproportionately low levels of ristocetin cofactor activity or collagen-binding capacity relative to VWF antigen. The abnormal platelet-dependent function is often associated with the absence of high molecular weight (HMW) multimers (type 2A, type 2B), but the HMW multimers may also be present (type 2M, some type 2B), and supranormal multimers may exist ("Vicenza" variant). The observation of a low FVIII-to-VWF:Ag ratio is a hallmark of type 2N VWD. in which the FVIII levels depend on the severity of the FVIII-binding defect. Today, the identification of mutations in particular domains of the pre-pro-VWF is helpful in classifying these variants and providing further insight into the structure-function relationship and the biosynthesis of VWF. Thus, mutations in the D2 domain, involved in the multimerization process, are found in patients with type 2A, formerly named IIC VWD. Mutations located in the D' domain or in the N terminus of the D3 domain define type 2N VWD. Mutations in the D3 domain characterize Vicenza and IIE patients. Mutations in the A1 domain may modify the binding of VWF multimers to platelets, either increasing (type 2B) or decreasing (type 2M, 2A/2M) the affinity of VWF for platelets. In type 2A VWD, molecular abnormalities identified in the A2 domain, which contains a specific proteolytic site, are associated with alterations in folding, impairing VWF secretion or increasing its susceptibility to proteolysis. Finally, a mutation localized in the carboxy-terminus CK domain, which is crucial for the dimerization of the VWF subunit, has been identified in a rare subtype 2A, formerly named IID.

Type 2 von Willebrand disease causing defective von Willebrand factor-dependent platelet function

Type 2 von Willebrand disease causing defective von Willebrand factor-dependent platelet function comprises mainly subtypes 2A, 2B and 2M. The diagnosis of type 2 von Willebrand disease may be guided by the observation of a disproportionately low level of ristocetin cofactor activity or collagen-binding activity relative to the von Willebrand factor antigen level. The decreased platelet-dependent function is often associated with an absence of high molecular weight multimers (types 2A and 2B), but the high molecular weight multimers may also be present (type 2M and some type 2B), and supranormal multimers may exist (as in the Vicenza variant). Today, the identification of mutations in particular domains of the pre-provon Willebrand factor is helpful to classify these variants and to provide further insight into the structure-function relationship and the biosynthesis of von Willebrand factor. Thus, mutations in the D2 domain, involved in the multimerization process, are found in patients with type 2A, formerly named IIC von Willebrand disease. Mutations in the D3 domain characterize the Vicenza variant, or type IIE patients. Mutations in the A1 domain may modify the binding of von Willebrand factor multimers to platelets, either increasing (type 2B) or decreasing (types 2M and 2A/2M) the affinity of von Willebrand factor for platelets. In type 2A disease, molecular abnormalities identified in the A2 domain, which contains a specific proteolytic site, are associated with alterations in folding that impair the secretion of von Willebrand factor or increase its susceptibility to proteolysis. Finally, a mutation localized in the C terminus cysteine knot domain, which is crucial for the dimerization of von Willebrand factor subunit, has been identified in a rare subtype 2A, formerly named IID.

Single-strand conformation polymorphism and heteroduplex analysis for gel-based mutation detection

Single-strand conformation polymorphism (SSCP) and heteroduplex analysis (HA) are popular electrophoretic methods for the identification of sequences. The principle reasons for the popularity of these two methods are their technical simplicity and their relatively high sensitivity for the detection of mutations. Here we review the theory and practice of SSCP and HA, including the factors contributing to the sensitivity of mutation detection. For SSCP analysis, these factors include: choice of gel matrix, electrophoretic conditions, presence of neutral additives, fragment size, and G+C content For HA, the principle factors influencing sensitivity are the gel matrix and the identity of the base mismatch.

Linkage analysis in haemophilia A: simultaneous genotyping of two polymorphisms of the human factor VIII gene using induced heteroduplex formation

Linkage analysis is currently the most widely used approach to genetic testing in families affected by haemophilia A. Among the polymorphisms of the factor VIII gene which can be used in such studies, a T/A polymorphism affecting a Bc/I restriction site in intron 18 and a G/A polymorphism in intron 7 are potentially useful. Both may be analysed by polymerase chain reaction (PCR) amplification followed by restriction endonuclease digestion and gel electrophoresis (the intron 7 polymorphism does not directly affect a restriction site but a minor sequence change in one PCR primer introduces an AlwNI site if the 'G' allele is present). We have developed a novel approach for the analysis of these two polymorphisms which uses induced heteroduplex formation to distinguish their allelic forms. Heteroduplex analysis eliminates the restriction endonuclease step and reduces the analysis for both loci to PCR followed directly by gel electrophoresis. Additionally, the new test has been designed to permit both loci to be analysed in the same PCR (multiplex heteroduplex analysis). Multiplex analysis was used to determine the allele frequencies of these polymorphisms in 105 factor VIII genes in the local (South Wales) population: BclI 'T'/BclI 'A' = 0.80/0.20 +/- 0.08 (95% confidence interval), intron 7 'G'/intron 7 'A' = 0.88/0.12 +/- 0.06 (95% confidence interval). The polymorphisms were found to be in strong linkage disequilibrium. The utility of multiplex heteroduplex analysis for linkage studies in haemophilia A was demonstrated by its application to carrier status investigation for an at risk female in a haemophilia A family.

Prenatal analysis of rhesus CcDEe blood groups by heteroduplex generator

OBJECTIVE

Our purpose was to determine the efficacy of the heteroduplex generator in the prenatal analysis of rhesus CcDEe blood groups.

STUDY DESIGN

A cross-sectional study was performed evaluating fetal samples from 85 women undergoing prenatal diagnosis and comparing the results with standard immunologic serotyping on cord blood delivery.

RESULTS

Of the 85 samples, 64 were tested, for all CcDEe alleles: one case was discrepant. Twenty-one cases were tested solely for the D antigen. Two novel genotypes were detected in the population by heteroduplex generator and confirmed by deoxyribonucleic acid sequencing. Five cases were indeterminate because of an indistinct banding pattern.

CONCLUSIONS

Heteroduplex analysis can identify rhesus blood group alleles and is inexpensive, rapid, and does not use radioactive isotopes.

Genetic screening and testing by induced heteroduplex formation

Clustered point mutations and small deletions or insertions within DNA are amenable to rapid analysis using induced heteroduplex formation. A single synthetic molecule (universal heteroduplex generator, UHG) may detect any of a series of such mutations following amplification by the polymerase chain reaction. This paper illustrates the use of UHG-based DNA heteroduplex analysis by describing the construction, properties, and methods of use of five UHGs, designed for genetic screening and testing of the inherited metabolic diseases: phenylketonuria, sickle-cell disease, cystic fibrosis, von Willebrand's disease type 2B, and mamman-binding lectin deficiency. In all cases, identification of multiple disease-associated genotypes is possible using a single UHG.