Molecular heterogeneity of inherited antithrombin III deficiency

Whole-exome sequencing identifies rare variants in STAB2 associated with venous thromboembolic disease

Deep vein thrombosis and pulmonary embolism, collectively defined as venous thromboembolism (VTE), are the third leading cause of cardiovascular death in the United States. Common genetic variants conferring increased varying degrees of VTE risk have been identified by genome-wide association studies (GWAS). Rare mutations in the anticoagulant genes PROC, PROS1 and SERPINC1 result in perinatal lethal thrombosis in homozygotes and markedly increased VTE risk in heterozygotes. However, currently described VTE variants account for an insufficient portion of risk to be routinely used for clinical decision making. To identify new rare VTE risk variants, we performed a whole-exome study of 393 individuals with unprovoked VTE and 6114 controls. This study identified 4 genes harboring an excess number of rare damaging variants in patients with VTE: PROS1, STAB2, PROC, and SERPINC1. At STAB2, 7.8% of VTE cases and 2.4% of controls had a qualifying rare variant. In cell culture, VTE-associated variants of STAB2 had a reduced surface expression compared with reference STAB2. Common variants in STAB2 have been previously associated with plasma von Willebrand factor and coagulation factor VIII levels in GWAS, suggesting that haploinsufficiency of stabilin-2 may increase VTE risk through elevated levels of these procoagulants. In an independent cohort, we found higher von Willebrand factor levels and equivalent propeptide levels in individuals with rare STAB2 variants compared with controls. Taken together, this study demonstrates the utility of gene-based collapsing analyses to identify loci harboring an excess of rare variants with functional connections to a complex thrombotic disease.

Identification of 2 Novel Polymorphisms and rs3138521 in 5′ Untranslated Region of SERPINC1 Gene in North Indian Population With Deep Vein Thrombosis

Antithrombin III (AT) is the most important endogenous anticoagulant, and genetic variability in SERPINC1, gene encoding AT, is low. Mutations leading to AT deficiency and increased thrombotic risk are well known; however, only 2 studies have reported mutations in regulatory region of SERPINC1 gene till date. Aim of the present study was to identify genetic variations in SERPINC1 5′ untranslated region (UTR) in Indian patients with deep vein thrombosis (DVT) having AT deficiency. DNA sequencing was used to identify underlying genetic defects in SERPINC1 regulatory region. In silico tools TFBIND and PROMO were used to identify transcription factor binding sites in the promoter region. We have identified 2 novel polymorphisms, g.25G>A and g.−1A>T, and 2 known g.67G>A and rs3138521 5′ UTR polymorphisms in SERPINC1 regulatory region in Indian patients with DVT for the first time. In present study, allele frequencies of rs3138521 (S: 0.37 and F: 0.63) were similar to that reported in Western population and were not associated with low plasma AT levels ( P value .5). This is the first report of regulatory region polymorphisms in SERPINC1 gene in Indian population. Our results strongly suggest that similar studies should be included when ever no mutation is detected in protein-coding region of AT gene.

Antithrombin III deficiency in Indian patients with deep vein thrombosis: identification of first India based AT variants including a novel point mutation (T280A) that leads to aggregation

Antithrombin III (AT) is the main inhibitor of blood coagulation proteases like thrombin and factor Xa. In this study we report the identification and characterization of several variants of AT for the first time in Indian population. We screened 1950 deep vein thrombosis (DVT) patients for AT activity and antigen levels. DNA sequencing was further carried out in patients with low AT activity and/or antigen levels to identify variations in the AT gene. Two families, one with type I and the other with type II AT deficiency were identified. Three members of family I showed an increase in the coagulation rates and recurrent thrombosis in this family was solely attributed to the rs2227589 polymorphism. Four members of family II spanning two generations had normal antigen levels and decreased AT activity. A novel single nucleotide insertion, g.13362_13363insA in this family in addition to g.2603T>C (p.R47C) mutation were identified. AT purified from patient's plasma on hi-trap heparin column showed a marked decrease in heparin affinity and thrombin inhibition rates. Western blot analysis showed the presence of aggregated AT. We also report a novel point mutation at position g.7549 A>G (p.T280A), that is highly conserved in serpin family. Variant protein isolated from patient plasma indicated loss of regulatory function due to in-vivo polymerization. In conclusion this is the first report of AT mutations in SERPINC1 gene in Indo-Aryan population where a novel point mutation p.T280A and a novel single nucleotide insertion g.13362_13363insA are reported in addition to known variants like p.R47C, p.C4-X and polymorphisms of rs2227598, PstI and DdeI.

Two concurrent chromosomal aberrations involving interstitial deletion in 1q24.2q25.2 and inverted duplication and deletion in 10q26 in a patient with stroke associated with antithrombin deficiency and a patent foramen ovale

Advanced high-throughput molecular cytogenetic analysis has enabled the identification of small chromosomal rearrangements, and two or more concurrently occurring chromosomal rearrangements have been identified using this technique. A girl with severe psychomotor developmental delay associated with an uncertain abnormality (detected by conventional karyotyping) in chromosome 10q had a sudden stroke at the age of 35 months. Laboratory and radiographic examinations revealed antithrombin (AT) deficiency and a patent foramen ovale (PFO). Two concurrent chromosomal aberrations, inverted duplication and deletion in the 10q26 region and a microdeletion in the 1q24.2q25.2 region including the AT gene (SERPINC1), were identified by microarray-based comparative genomic hybridization analysis. Both chromosomal aberrations were found to be of paternal origin. This study described the concurrence of chromosomal rearrangements involving two chromosomes, and estimated the frequency of two or more chromosomal aberrations as 2-4%.

Anticoagulant heparan sulfate to not clot--or not?

Vascular endothelial cells (ECs) produce anticoagulant heparan sulfate (HSAT+)-a small subpopulation of heparan sulfate (HS) containing a specific pentasaccharide motif with high affinity for plasma antithrombin (AT). This pentasaccharide is responsible for the anticoagulant action of therapeutic heparin, which dramatically catalyzes AT neutralization of coagulation proteases. Consequently, HSAT+ has been designated as "anticoagulant HS," and has long been thought to convey antithrombotic properties to the blood vessel wall. The Hs3st1 gene encodes HS 3-O-sulfotransferase-1, whose rate limiting action regulates EC production of HSAT+. To elucidate the biologic role of HSAT+, we generated Hs3st1-/- knock-out mice that have undetectable EC HSAT+. Despite long held historic expectations, hemostasis was unaffected in Hs3st1-/- mice. In light of this surprising finding, herein we evaluate historic, biochemical, kinetic, physiologic, and molecular genetic studies of AT, heparin, and HSAT+. We find that a hemostatic role for HSAT+ cannot presently be excluded; however, HSAT+ may well not be essential for AT's anticoagulant function. Specifically, in the absence of glycosaminoglycans, physiologic levels of AT can neutralize coagulation proteases at a sufficiently high throughput to account for most of AT's anticoagulant function. Moreover, at the vessel wall surface, glycosaminoglycans distinct from HSAT+ may be the predominant catalysts of AT's anticoagulant activity. We then explore the possibility that HSAT+ regulates a less well known function of AT, anti-inflammatory activity. We find that Hs3st1-/- mice exhibit a strong proinflammatory phenotype that is unresponsive to AT's anti-inflammatory activity. We conclude that the predominant function of HSAT+ is to mediate AT's anti-inflammatory activity.

Genetic variations and their influence on risk and treatment of venous thrombosis

Venous thrombosis (VT) is a highly prevalent disease. Risk factors can be genetic or acquired. The well-established genetic polymorphisms predisposing to thrombophilic disorders can be divided into rare 'loss-of-function mutations' in anticoagulant proteins and common 'gain-of-function mutations' in procoagulant proteins, which are weaker risk factors. In addition to functional polymorphisms, defects in common pathways affecting biosynthesis or clearance of plasma coagulation factors and their relations to VT risk have been detected. Recently, investigations regarding genetic variations and response to drug treatment, relevant for the pathogenesis as well as therapy of venous thromboembolism have been performed. The methodical advances in genetic research have led to the identification of a number of new variants with still unclear association to VT. This review aims to discuss the established genetic risk factors as well as some candidate predictors of VT. Further, the recent developments in pharmacogenomics are reviewed.

The impact of new methods of gene analysis on screening for genetic disease

Genetic disease is a major cause of childhood mortality and morbidity in developed countries and is an increasing problem in Third World countries. Recently developed techniques of direct gene analysis may provide a valuable approach for carrier detection and prenatal diagnosis of a significant number of single-gene disorders. However, there are many organizational and educational problems to overcome before this new technology can be adapted for widespread clinical use.

The inherited thrombophilias: genetics, epidemiology, and laboratory evaluation

It is now possible to identify a predisposing thrombophilic condition for venous thrombosis in well over half of the cases. Certain thrombophilia diagnoses have a major impact on anticoagulant therapy, and hence it is incumbent upon physicians to understand how to diagnose and manage these conditions. This chapter covers the genetics and epidemiology of the inherited thrombophilias and provides a useful, common-sense approach to the laboratory evaluation of a patient with venous thrombosis.

[Antithrombin deficiency and thrombosis in a young child]

BACKGROUND

Thromboses represent a rare event in children and may be due to a deficiency of antithrombin.

CASE REPORT

A 10-year-old boy developed thrombosis due to a congenital quantitative deficiency in antithrombin, confirmed by molecular biology. His father was diagnosed with the same deficiency. The child was first treated with heparin and is now on antivitamin K. He is well 26 months after diagnosis.

CONCLUSION

When a young patient presents with a thrombotic event, a congenital deficiency in one of the inhibitors of coagulation, one of which is antithrombin, should be looked for and the condition treated as soon as possible.

Molecular genetics of antithrombin deficiency

Antithrombin is the major proteinase inhibitor of thrombin and other blood coagulation proteinases. Antithrombin has two functional domains, a heparin binding site and a reactive centre (that complexes and inactivates the proteinase). Its deficiency results in an increased risk of venous thromboembolism. Appreciable progress has been made in recent years in understanding the structure and function of this protein, the genetic cause of inherited deficiency and its clinical consequence. The structure of antithrombin is now considered in terms of the models derived from X-ray crystallography, which have provided explanations for the function of its heparin interaction site and of its reactive loop. The structural organization of the antithrombin gene has been defined and numerous mutations have been identified that are responsible for antithrombin deficiency: these may reduce the level of the protein (Type I deficiency), alter the function of the protein (Type II deficiency, altering heparin binding or reactive sites), or even have multiple or 'pleiotropic effects' (Type II deficiency, altering both functional domains and the level of protein).

Molecular genetics of human antithrombin deficiency

Human antithrombin is the major plasma inhibitor of thrombin both in the presence and absence of heparin. Its physiological importance is emphasised by the recurrent thromboses that individuals with a deficient or functionally abnormal protein are prone to develop. Such deficiencies are estimated to affect as many as 1:630 of the general population and between 3% and 5% of patients with thrombotic disease. The gene for antithrombin (AT3) has been cloned and shown to map to the long arm of chromosome 1 at 1q23-25. The gene consists of seven exons and six introns and spans 13,477bp of DNA. Advances in molecular genetic techniques have facilitated identification of the underlying DNA mutation(s) in > 80 families with antithrombin deficiency. Such work has proved invaluable in structure-function studies and in helping to provide informed genetic counselling to "at-risk" individuals based upon the natural history of similar variants.

Deep venous thrombosis and pulmonary embolism after lung transplantation

The incidence of deep venous thrombosis or pulmonary embolism after lung or heart-lung transplantation has not been well defined. Pulmonary embolism may be of particular concern in the postoperative period owing to an inadequately developed or absent collateral bronchial circulation and potential risk of pulmonary infarction. Fourteen (12.1%) of 116 patients undergoing either lung (n = 87) or heart-lung (n = 29) transplantation developed thromboembolic complications 10 days to 36 months after operation. Deep vein thrombosis developed in nine patients, including three with upper body thrombosis related to indwelling central venous catheters. Seven patients (6%) had pulmonary embolism, and three of them died. Resolution of pulmonary embolism was successfully accomplished by selective pulmonary artery infusion of urokinase in three patients without complications. Our experience indicates that deep vein thrombosis and pulmonary embolism are significant problems after lung transplantation. Mortality is high in those patients in whom pulmonary embolism develops. Therefore, a comprehensive prevention protocol is warranted.

The molecular genetics of familial venous thrombosis

This study of naturally occurring mutations predisposing to venous thrombosis has led to a number of important advances in our understanding of protein structure and function relationships and the molecular basis of gene mutation. It has also potentiated the accurate and reliable presymptomatic and antenatal detection of predisposing gene lesions. Perhaps the major challenge facing us is the probabilistic nature of thromboembolism; only a certain proportion of patients with recognized gene defects predisposing to thrombosis will actually suffer from thrombotic episodes. Environmental insults of various kinds, and perhaps epistatic effects resulting from the influence of other loci, are likely to be contributory factors and will help to determine whether a thrombotic event occurs in individuals already compromised by a defect in a gene whose malfunction is known to predispose to thrombosis. Since molecular genetic techniques allow us to dissect the allelioheterogeneity of the different deficiency states by characterizing the wide spectrum of gene mutations giving rise to thrombosis, it may eventually prove possible to relate specific gene lesions to the probability of thromboembolism as well as to the severity and frequency of thrombotic episodes. The multifactorial nature of thrombosis demands a multidisciplinary approach to the analysis of its causation, early detection, treatment and prevention. The application of the new and powerful techniques of molecular genetics promises to make a substantial contribution to all aspects of thrombosis research.

Antithrombin and its inherited deficiencies

Human antithrombin is the major inhibitor of the coagulation serine proteases accounting for approximately 80% of the thrombin inhibitory activity of plasma. It is a member of the serpin family of serine protease inhibitors and in common with some other members of this family it undergoes a dramatic increase in its inhibitory activity in the presence of heparin and other sulphated glycosaminoglycans. Two functional domains in antithrombin are recognised, the reactive site domain which interacts with the active site serine residue of the protease and the heparin binding domain. The gene for antithrombin has been cloned and its entire nucleotide sequence determined. A deficiency or functional abnormality of antithrombin may result in an increased risk of thromboembolic disease. Such deficiencies are estimated to affect as many as 1:300 of the general population and 3 to 5% of patients with thrombotic disease. On the basis of functional and immunological antithrombin assays, antithrombin deficiency may be subdivided into Types I and II. Type I disease is due to a wide variety of heterogeneous DNA mutations whilst in Type II disease missense mutations leading to single amino acid substitutions have been identified in all cases. Clinically, Type I antithrombin deficiency is associated with recurrent thromboembolic disease whereas in Type II deficiency the risk of thrombosis is closely related to the position of the mutation within the protein. Thus, heterozygotes with mutations within the heparin binding domain of antithrombin have a relatively low risk of thrombosis compared to those with mutations at or close to the reactive site of the molecule.

(ATT) trinucleotide repeats in the antithrombin gene and their use in determining the origin of repeated mutations

Two (ATT) trinucleotide repeat polymorphisms have been identified in the tails of Alu repeat elements in intron 5 of the antithrombin gene. The frequency and distribution of allele sizes for the Alu 5 and Alu 8 tail polymorphisms have been defined in a sample Caucasian population. The Alu 5 polymorphism has two alleles while that of Alu 8 has 10 alleles with a heterozygosity of 0.83. These polymorphisms have been used in combination with four previously described polymorphisms within the antithrombin gene to construct antithrombin gene haplotypes in the sample Caucasian population. Twenty-two different haplotypes were observed, with the Alu 8 polymorphism being particularly useful in subdividing the core haplotype based on the previously identified polymorphisms. The haplotype data were used to investigate the origin of repeat mutations within the antithrombin locus. We compared the haplotypes associated the mutant antithrombin genes in five families with the mutation 2759C-->T (L99F) and five families with the mutation 5381C-->T (R129Stop). The mutation 2759C-->T (L99F), which occurs within a non-CpG dinucleotide, was carried on a gene associated with an identical haplotype in each of the five families. The mutation 5381C-->T (R129Stop), a single base substitution within a CpG dinucleotide, was associated with at least two different haplotypes. The findings suggest a founder effect in the five families sharing the 2759C-->T (L99F) and at least two independent origins for the CpG dinucleotide mutation 5381C-->T (R129Stop).

Pleiotropic effects of antithrombin strand 1C substitution mutations

Six different substitution mutations were identified in four different amino acid residues of antithrombin strand 1C and the polypeptide leading into strand 4B (F402S, F402C, F402L, A404T, N405K, and P407T), and are responsible for functional antithrombin deficiency in seven independently ascertained kindreds (Rosny, Torino, Maisons-Laffitte, Paris 3, La Rochelle, Budapest 5, and Oslo) affected by venous thromboembolic disease. In all seven families, variant antithrombins with heparin-binding abnormalities were detected by crossed immunoelectrophoresis, and in six of the kindreds there was a reduced antigen concentration of plasma antithrombin. Two of the variant antithrombins, Rosny and Torino, were purified by heparin-Sepharose and immunoaffinity chromatography, and shown to have greatly reduced heparin cofactor and progressive inhibitor activities in vitro. The defective interactions of these mutants with thrombin may result from proximity of s1C to the reactive site, while reduced circulating levels may be related to s1C proximity to highly conserved internal beta strands, which contain elements proposed to influence serpin turnover and intracellular degradation. In contrast, s1C is spatially distant to the positively charged surface which forms the heparin binding site of antithrombin; altered heparin binding properties of s1C variants may therefore reflect conformational linkage between the reactive site and heparin binding regions of the molecule. This work demonstrates that point mutations in and immediately adjacent to strand 1C have multiple, or pleiotropic, effects on this serpin, leading ultimately to failure of its regulatory function.

The antithrombin III gene polymorphism in Japan: Examination for haplotypes relevant to disordered antithrombin III biosynthesis

In the human antithrombin III (AT III) gene of Caucasian, two restriction fragment length polymorphism (RFLPs) have been identified and used for the linkage analysis of many congenital AT III abnormality and deficiency. In the present study, we attempted to examine the existence and distribution of these RFLPs in Japanese and utilize them for the molecular survey of the members in the AT III Toyama kindred and 4 type Ia deficient families. An AT III cDNA clone was isolated by ourselves and served as a hybridization probe. In Japanese, the intragenic polymorphism, which is referred to + and - alleles, was evenly distributed (.49: .51), and the 5'-length polymorphism, designated as S and F alleles, was also conserved at a ratio of .4 to .6. However, the combined genotypes of both polymorphisms revealed disproportionate, and + and S, and - and F alleles seemed mainly to coexist. AT III genes of the AT III Toyama kindred showed the homozygous genotype of -/F, and all affected members of the deficient families demonstrated no distinguishable alterations on Southern blots, suggesting that a subtle defect in the AT III gene or the "trans-acting" disordered mechanism is responsible for the decreased AT III levels. According to some reports that a defective AT III gene is the cause of inherited AT III deficiency, it was implied that the abnormal AT III gene was located on the haplotype of -/F in 3 families and +/F in one. In two deficient families with heterozygous genotypes, the RFLPs were considered to bring a clue to determine the structural changes.

Antithrombin Glasgow II: alanine 382 to threonine mutation in the serpin P12 position, resulting in a substrate reaction with thrombin

A female with recurrent thrombosis was found to have a functional abnormality of antithrombin, with a ratio of functional to immunological activity in plasma of approximately 50%. Crossed immunoelectrophoresis in the presence of heparin was normal, indicating an abnormality of the reactive site, rather than the heparin binding domain. Accordingly, the antithrombin was isolated by heparin-Sepharose chromatography: this produced a mixture of normal and variant antithrombin, as the patient was heterozygous for the abnormality. To remove the normal component, the antithrombin was passed through a column of thrombin-Sepharose. On sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), prior to its application to thrombin-Sepharose, the antithrombin migrated as a single band with identical mobility to that of normal antithrombin. After thrombin-Sepharose, the purified variant component was proteolysed, and migrated as two components, one with a reduced and one with enhanced mobility under non-reducing conditions. This demonstrated that the variant was unable to form stable inhibitor-thrombin complexes and was cleaved in a substrate reaction with thrombin. One site of cleavage was unambiguously ascertained to be the Arg 393-Ser 394 reactive site bond, by NH2 terminal sequencing of the cleaved variant antithrombin: 10 steps beginning at the P1' position, Ser-Leu-Asn-Pro-Asn-Arg,..., were clearly identified. The mutation responsible for this defect was studied by polymerase chain reaction (PCR) amplification of exon 6 of the antithrombin gene and direct sequencing of the amplified product. The presence of both a G and A in the first position of codon 382, identified the mutation GCA to ACA, which results in the substitution of Ala 382 to Thr. This is identical to that reported for antithrombin Hamilton (Devraj-Kizuk et al, 1988), although antithrombin gene polymorphism analysis suggests that the antithrombin Glasgow II mutation has arisen independently. We have recently shown (Caso et al, 1991) that mutation at a nearby position, Ala 384 to Pro, also transforms another variant, antithrombin Vicenza/Charleville, into a substrate for thrombin. The present results with antithrombin Glasgow II suggest that all the alanine residues at the base of the reactive site loop in positions P12-10 may be important for the formation of a stabilized inhibitor-thrombin complex.

Review of hypercoagulability syndromes: what the interventionalist needs to know

Although none of these syndromes are very common, they are nevertheless of sufficient prevalence to be identified on occasion in the practice of the busy interventionalist or surgeon. Furthermore, it is anticipated that many more specific hypercoagulability disorders will be identified in the future. Therefore, it is necessary for the nonhematologist practitioner to be aware of their existence and to know when to seek hematology consultation to appropriately evaluate suspected individuals. Several clinical indicators should raise one's index of suspicion. One should be concerned about the patient with a strong family history of recurrent arterial and/or venous thrombosis or a history of previous arterial and/or venous thromboemboli without predisposing factors. Laboratory screening should be initiated for the patient who has had thrombotic events occurring at unusual sites, such as the upper extremity or mesenteric venous circulations, or in young patients presenting with thrombotic events. Patients with chronic arteriosclerotic disease at a young age, with evidence of rapidly progressive atherosclerotic lesions, and especially those who experience early occlusion after uncomplicated surgical or endovascular procedures warrant evaluation. Furthermore, patients manifesting a resistance to therapeutic anticoagulation with conventional agents may also be affected by one of these disorders. Identification of an underlying hypercoagulability disorder will not only influence the decision to proceed with a therapeutic intervention for noncritical arterial insufficiency but will also dictate appropriate pharmacologic management of the hypercoagulable patient to reduce potential thrombotic complications when vascular interventions are performed.

Site-directed mutagenesis of alanine-382 of human antithrombin III

Antithrombin III Hamilton is a structural variant of antithrombin III (AT-III) with normal heparin affinity but impaired serine protease inhibitory activity. The molecular defect of AT-III-Hamilton is a substitution of threonine for alanine at amino acid residue 382. Recently it has been shown that both plasma-derived and cell-free-derived AT-III-Hamilton polypeptides act as substrates rather than inhibitors of thrombin and factor Xa. In the present study, the cell-free expression phagemid vector pGEM-3Zf(+)-AT-III1-432 was mutated at amino acid residue 382 of AT-III to generate 7 cell-free-derived variants. All these cell-free-derived AT-III variants were able to bind heparin as effectively as cell-free-derived normal AT-III. In terms of alpha-thrombin inhibitory activity each variant reacted differently. Variants could be grouped into 3 categories with respect to thrombin-AT-III complex formation: (1) near normal activity (glycine, isoleucine, leucine, valine); (2) low activity (threonine, glutamine); (3) no detectable activity (lysine). These data suggest that mutations at position 382 of AT-III may have a variable effect on protease inhibitory activity, depending on either the stability of the P12-P9 region of the exposed loop of AT-III, or the inability of the amino acid residue at position 382 to interact with a conserved hydrophobic pocket consisting of phenylalanine (at positions 77, 221 and 422) and isoleucine (position 412) residues.

The molecular genetics of familial venous thrombosis

Inherited defects of antithrombin III, protein C, protein S, heparin cofactor II, plasminogen and the fibrinogens are thought to be responsible for between 10 and 15% of all patients presenting with recurrent venous thrombosis. The structure, function and expression of these genes and the nature of the gene lesions underlying the deficiency states are reviewed in detail.

Antithrombin III-Amiens: a new family with an Arg47----Cys inherited variant of antithrombin III with impaired heparin cofactor activity

A family with an antithrombin III variant (AT-III-Amiens) demonstrating abnormal heparin cofactor activity is described. Amplification and direct sequencing of genomic DNA by the polymerase chain reaction procedure permitted the identification of an Arg47----Cys mutation in exon 2 of the variant antithrombin III gene.

DdeI polymorphism in intron 5 of the ATIII gene

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A genetic map of chromosome 1: comparison of different data sets and linkage programs

We have used 22 chromosome 1 loci to construct a genetic linkage map of this autosome using the Venezuelan Reference Pedigree. These markers formed two linkage groups separated by an interval of more than 30 cM. Linkage maps were constructed separately using the computer programs LINKAGE and MAPMAKER to determine their relative speed, efficiency, and accuracy. We found that both programs generated maps with the same order and distances, although the LINKAGE program derived more information from the data, allowing placement of one additional marker. Many of the probes have previously been mapped using the CEPH pedigrees. However, the current map is generated from a different data set and so can be used to increase the certainty of locus order and map position. Ultimately, the generation and confirmation of a 1-cM map of this chromosome will require such multiple data sets.

Restriction fragment length polymorphisms of X chromosome among Japanese population

Restriction fragment length polymorphisms were studied among the Japanese using 13 polymorphic DNA probes on the X chromosome. For 6 probes (pPA4B, cpX203, p58-1, pHPGK-7e, cpX289 and 7b) the allelic frequencies were the same as those for Caucasians, but they were quite different (p less than 0.01) for 4 probes (dic56, pOTC (MspI), pTAK8B and pXG-16 (HindIII)). No polymorphisms were observed for 4 probes (pG95 alpha 1-7dIII/RI (n (chromosome number studied) = 54), pXG-16 (TaqI) (n = 50, p8 (n = 108), and pXG-17 (n = 76). These results suggest that not a small number of DNA probes currently available are useless for linkage analysis in Japan.

Antithrombin: structure, genomic organization, function and inherited deficiency

Antithrombin is a major plasma protein inhibitor of proteinases generated during blood coagulation; it plays an important role in the regulation of thrombin in blood. The anticoagulant heparin greatly accelerates the rate of inactivation of proteinases by antithrombin, predominantly through its well defined, highly specific binding reaction with the inhibitor, but also through a less strictly defined interaction with some of the proteinases (such as thrombin). There is evidence for an analogous acceleratory mechanism in vivo, that functions by the binding of antithrombin to a subpopulation of heparan sulphate proteoglycans intercalated in the surface of endothelial cells. The location and structure of the gene for antithrombin are known. Both its overall organization and the structure of the subdomains of the expressed protein can be considered in terms of their relationships to a serine proteinase inhibitor superfamily, which is believed to have evolved from a common ancestor. The region of the antithrombin gene 5' to the coding region has been characterized. Unlike other members of the serpin family, there is no TATA-like promoter sequence. Two enhancer sequences have been identified that are homologous to enhancer regions of other genes. There are two polymorphisms: an intragenic polymorphism arising from a translationally silent A to G transition in codon 305, and a length polymorphism arising from the presence of 32 bp or 108 bp non-homologous sequences 345 bp upstream from the translation initiation codon. Inherited deficiency of antithrombin is associated with familial thromboembolism. The molecular genetic basis of some subtypes of deficiency is increasingly yielding to investigation. It is interesting to note that a number of mutations have been identified in CpG dinucleotides, supporting the suggestion that this dinucleotide sequence may represent a mutation hotspot in the human genome.

Molecular genetics of inherited antithrombin III deficiencies

The cloning of antithrombin III (ATIII) complementary deoxyribonucleic acids and the determination of the ATIII gene structure have permitted a systematic evaluation of the molecular basis for inherited ATIII deficiencies. Sixteen kindreds with the most common form of the deficiency, in which plasma ATIII antigen levels and activity are proportionately reduced, were studied. Two polymorphic deoxyribonucleic acid markers were used to resolve parental ATIII alleles and to trace their inheritance patterns. In 15 of 16 cases, the structure of the affected ATIII allele was indistinguishable from normal, suggesting that relatively small mutations, resulting in gene inactivation, are responsible for the lower ATIII levels in these affected families. In the remaining kindred, complete deletion of one ATIII allele was seen. Also investigated was the molecular basis for a qualitative form of ATIII deficiency in a French-Canadian family with normal levels of immunoreactive protein but only half the expected levels of serine protease inhibitor activity. Using polymorphic markers, the abnormal allele was identified, cloned, and partially sequenced from the propositus. A single G----A transition was seen in the first base of codon 382, resulting in an alanine----threonine substitution in the defective protein. This mutation, together with others in this vicinity, defines a minimal length for a fully functional thrombin-binding domain.

Type I C1 inhibitor deficiency with a small messenger RNA resulting from deletion of one exon

The molecular genetic basis of C1 inhibitor (C1 INH) deficiency in a patient with type I hereditary angioneurotic edema was studied. This patient was found to have an abnormally short C1 INH mRNA together with a normal message. Restriction fragment length polymorphism of the C1 INH gene was detected by Southern blot analysis of the patient's DNA after digestion with Pst I or Sac I, and hybridization with a full-length C1 INH cDNA. Hybridization of the same blot with three different fragments of the full-length cDNA suggested that exon VII and portions of both flanking introns were deleted in the C1 INH gene. Northern blot analysis of RNA from cultured monocytes, using a probe corresponding to exon VII, also indicated that the abnormal C1 INH mRNA had a deletion of these nucleotides. To confirm the hypothesis that the short C1 INH mRNA contained a deletion, the involved segment of the patient's C1 INH mRNA was amplified using the polymerase chain reaction (PCR). PCR amplification yielded two C1 INH DNA fragments of different lengths (380 and 160 bp). Southern blot and sequence analysis of both DNA fragments clearly revealed that the smaller 160-bp DNA was derived from the abnormal message and had a deletion of nucleotides corresponding to exon VII.

Diagnosis of genetic disorders at the DNA level

In the past 10 years considerable progress has been made in the diagnosis of hereditary disorders at the DNA level. Many monogenic disorders can now be examined at the gene level; such examination has led to a better understanding of the molecular basis of these disorders and made carrier detection and prenatal diagnosis possible. Each year, more and more monogenic disorders can be added to the list of diseases that can be diagnosed by DNA analysis. Future research will be devoted to the identification of genes responsible for other known monogenic hereditary disorders, the elucidation of the molecular lesion associated with chromosomal abnormalities, and the characterization of the genes and gene defects involved in the common multifactorial diseases. The goal of diagnosis is the identification of the genetic defect in affected patients, persons destined to be affected, and carriers.

Antithrombin III deficiency

A moderate reduction of plasma antithrombin activity is an uncommon but clinically important cause of severe thromboembolic disease. In recent years the molecule responsible for the major part of this activity (antithrombin III) has been extensively characterised and the mode of inheritance of familial deficiencies worked out. Over 30 autosomally dominant inheritable variants have been described, the gene for normal human antithrombin III has been sequenced and this information has provided important insights into the reaction of antithrombin with thrombin and the catalytic role of heparin. Further information has been derived by analogy with other serine proteinase inhibitors, in particular alpha 1 antitrypsin. Recombinant DNA methods have been used to produce functionally active AT III which may, in the future, replace human chromatographically-separated AT III as the treatment of choice for clinically important deficiency states. Newer diagnostic techniques, using restriction fragment length polymorphisms and synthetic oligonucleotide probes, hold the promise of more accurate diagnosis and diagnosis in the antenatal period in families possessing some of the fully characterised variants.

Inherited factors in thrombosis

Patients with inherited defects or abnormalities that impair the naturally-occurring anticoagulant and fibrinolytic systems are at risk of developing venous and, more rarely, arterial thromboembolism. The prevalence of inherited thrombophilia in the general population is higher than that of inherited bleeding disorders (ca. 1 in 7500 vs 1 in 20,000). Low levels or dysfunctional forms of antithrombin III, protein C and protein S and abnormal fibrinogens are the most frequent and well-established inherited causes for thrombosis. Less frequent and/or less established causes are low heparin cofactor II and plasminogen and high levels of plasminogen activator inhibitor and histidine-rich glycoprotein. The pathophysiology, genetic and clinical aspects and laboratory diagnosis of inherited thrombotic disorders are reviewed and an approach to prophylaxis and therapy is outlined.

Recent advances in the management of venous thromboembolism

Deep venous thrombosis and pulmonary embolism are frequently diagnosed in patients encountered in a primary-care practice. In the past 10 years, many important advances have been made regarding the management of these disorders. Risk factors have been better defined than in the past. Several new prophylactic measures--such as external pneumatic compression of the lower extremities, dihydroergotamine in combination with heparin, adjusted-dose heparin, and two-step warfarin therapy--can be used to help prevent deep venous thrombosis in surgical patients. The use of serial impedance plethysmography has expanded options for noninvasive diagnosis of deep venous thrombosis. Correlations between pulmonary embolism and ventilation-perfusion lung scan patterns have been clarified. Although much has been learned about heparin and warfarin that affect common management decisions, the indications for thrombolytic therapy for venous thromboembolism remain controversial. Finally, studies have shown that calf vein thrombi that are not detectable by impedance plethysmography and that show no evidence of proximal propagation by serial impedance plethysmography do not require treatment.

Genetic studies of low abundance human plasma proteins. VIII. Inherited structural variation in antithrombin III

Genetically determined structural polymorphism of antithrombin III has been observed using ultra narrow pH polyacrylamide isoelectric focusing gels, followed by immunoblotting. The products of three alleles at the antithrombin III structural locus have been detected in normal U.S. white and black blood donors. The frequencies of the three alleles, AT III* 1, AT III* 2 and AT III* 3, respectively, are: 0.878, 0.103, 0.019 in whites and 0.916, 0.068, 0.016 in blacks. Family data from a large number of families establish an autosomal codominant pattern of inheritance of the three alleles.

Evidence linking familial thrombosis with a defective antithrombin III gene in two British kindreds

Using DNA probes in a structural study of the antithrombin III gene locus we found no evidence of gene deletion in two British kindreds with inherited antithrombin III deficiency. However, linkage analysis between a common DNA polymorphism and the antithrombin III deficiency trait showed that the defect lies at or close to the antithrombin III structural gene. The lod score for linkage within the larger Scottish kindred was 3.1 (theta = 0). These results are consistent with previously published data suggesting that mutation of the antithrombin III structural gene is the cause of inherited antithrombin III deficiency in some families.

Further characterization of a pathological isoantithrombin with no affinity for heparin (antithrombin III Roma)

A molecular antithrombin III variant (Antithrombin III Roma) with an abnormal pattern of crossed immunoelectrofocusing was further investigated in order to identify the pathological isoforms. AT III crossed immunoelectrofocusing of the whole plasma from the affected patients showed a loop overlapping the peak normally present at pH 4.8-4.6. Affinity chromatography demonstrated the presence of an AT III fraction totally lacking in heparin affinity. Crossed immunoelectrophoresis on heparin-agarose (H-CIE) and crossed immunoelectrofocusing (CIEF) runs performed on the fractions obtained by heparin-agarose affinity chromatography confirmed that the functional defect was exclusively related to the pathological isoantithrombin (pH 4.8-4.6), which was also devoid of any progressive activity. The AT III fraction with normal affinity to heparin displayed H-CIE and CIEF patterns identical to the control AT III.

Thrombosis in inherited deficiencies of antithrombin, protein C, and protein S

The coagulation cascade can be pictured as a series of reactions in which a zymogen, a cofactor, and a converting enzyme interact to form a multimolecular complex on a natural surface. In each case, the four reactants must be present if the conversion of a zymogen to the corresponding serine protease is to take place at any significant rate. The principal natural anticoagulant systems that are able to exert damping effects on the various steps of the cascade are the heparin-antithrombin and protein C-thrombomodulin mechanisms that regulate the serine proteases and the cofactors or activated cofactors, respectively. Inherited thrombotic disorders associated with specific deficiencies of antithrombin, protein C, and protein S have been described. This review describes the biochemistry and physiology of these endogenous anticoagulant systems. The development of specific radioimmunoassay techniques for prothrombin activation fragment F1 + 2, fibrinopeptide A, and protein C activation peptide has allowed us to carry out studies of these endogenous regulatory mechanisms involved in thrombin generation in patients with deficiencies of antithrombin or protein C. This information is then used to construct a framework for understanding the pathophysiology of the prethrombotic and actively thrombotic states in humans with these clinical disorders.

DNA analysis in human disease

The analysis of human DNA using recombinant DNA technology is fast becoming an integral part of the diagnosis, assessment, and prevention of inherited and somatic genetic disease. The rationale underlying these methods of analysis is discussed, and the nature and extent of mutational change in heritable disorders and neoplastic development is outlined.