Haemophilia A: database of nucleotide substitutions, deletions, insertions and rearrangements of the factor VIII gene

F8/F9 variants in the population-based PedNet Registry cohort compared with locus-specific genetic databases of the European Association for Haemophilia and Allied Disorders and the Centers for Disease Control and Prevention Hemophilia A or Hemophilia B Mutation Project

Background

Hemophilia A and B are caused by variants in the factor (F) VIII or FIX gene. Selective reporting may influence the distribution of variants reported in genetic databases.

Objectives

To compare the spectrum of F8 and F9 variants in an international population-based pediatric cohort (PedNet Registry) with the spectrum found in the European Association for Haemophilia and Allied Disorders (EAHAD) and the Centers for Disease Control and Prevention Hemophilia A or Hemophilia B Mutation Project (CHAMP/CHBMP) databases.

Methods

All patients registered in the PedNet Registry on January 1, 2021 were included in this study. As comparators, data from patients with severe hemophilia included in the CHAMP/CHBMP registry (US center data) and EAHAD were used.

Results

Genetic information was available for 1941 patients. Intron 22 inversion was present in 52% of patients with severe hemophilia A; frameshift (36%), missense (28%), and nonsense (20%) were the most frequent variants in patients with severe hemophilia A who were inversion-negative. The most frequent variants in severe hemophilia B were missense (48%). In nonsevere disease, most variants were missense variants (moderate hemophilia A: 91%; mild hemophilia A: 95%, moderate and mild hemophilia B: 86% each). Comparison with the databases demonstrated a higher proportion of missense variants associated with severe hemophilia B in EAHAD (68%) than in PedNet (48%) and CHBMP (46%).

Conclusion

The PedNet population-based cohort provides an alternative to the established databases, which collect data by selective reporting, as it is a well-maintained database covering the full spectrum of pathogenic F8 and F9 variants, and indicates the number of patients affected by each particular variant.

SAXS analysis of the intrinsic tenase complex bound to a lipid nanodisc highlights intermolecular contacts between factors VIIIa/IXa

The intrinsic tenase (Xase) complex, formed by factors (f) VIIIa and fIXa, forms on activated platelet surfaces and catalyzes the activation of factor X to Xa, stimulating thrombin production in the blood coagulation cascade. The structural organization of the membrane-bound Xase complex remains largely unknown, hindering our understanding of the structural underpinnings that guide Xase complex assembly. Here, we aimed to characterize the Xase complex bound to a lipid nanodisc with biolayer interferometry (BLI), Michaelis-Menten kinetics, and small-angle X-ray scattering (SAXS). Using immobilized lipid nanodiscs, we measured binding rates and nanomolar affinities for fVIIIa, fIXa, and the Xase complex. Enzyme kinetic measurements demonstrated the assembly of an active enzyme complex in the presence of lipid nanodiscs. An ab initio molecular envelope of the nanodisc-bound Xase complex allowed us to computationally model fVIIIa and fIXa docked onto a flexible lipid membrane and identify protein-protein interactions. Our results highlight multiple points of contact between fVIIIa and fIXa, including a novel interaction with fIXa at the fVIIIa A1-A3 domain interface. Lastly, we identified hemophilia A/B-related mutations with varying severities at the fVIIIa/fIXa interface that may regulate Xase complex assembly. Together, our results support the use of SAXS as an emergent tool to investigate the membrane-bound Xase complex and illustrate how mutations at the fVIIIa/fIXa dimer interface may disrupt or stabilize the activated enzyme complex.

Structure of blood coagulation factor VIII in complex with an anti-C1 domain pathogenic antibody inhibitor

Antibody inhibitor development in hemophilia A represents the most significant complication resulting from factor VIII (fVIII) replacement therapy. Recent studies have demonstrated that epitopes present in the C1 domain contribute to a pathogenic inhibitor response. In this study, we report the structure of a group A anti-C1 domain inhibitor, termed 2A9, in complex with a B domain-deleted, bioengineered fVIII construct (ET3i). The 2A9 epitope forms direct contacts to the C1 domain at 3 different surface loops consisting of Lys2065-Trp2070, Arg2150-Tyr2156, and Lys2110-Trp2112. Additional contacts are observed between 2A9 and the A3 domain, including the Phe1743-Tyr1748 loop and the N-linked glycosylation at Asn1810. Most of the C1 domain loops in the 2A9 epitope also represent a putative interface between fVIII and von Willebrand factor. Lastly, the C2 domain in the ET3i:2A9 complex adopts a large, novel conformational change, translocating outward from the structure of fVIII by 20 Å. This study reports the first structure of an anti-C1 domain antibody inhibitor and the first fVIII:inhibitor complex with a therapeutically active fVIII construct. Further structural understanding of fVIII immunogenicity may result in the development of more effective and safe fVIII replacement therapies.

Discrepant Hemophilia A: An Underdiagnosed Disease Entity

OBJECTIVES

The term discrepant hemophilia A (DHA) denotes the discrepancy between factor VIII activity (FVIII:C) measured by different assay methodologies in patients with nonsevere hemophilia A (HA). The objective was to review the characteristics and the current understanding of mechanisms contributing to assay discrepancy in DHA.

METHODS

Characteristics of the DHA patients treated were examined by retrospective chart review. In addition, a literature review was performed to determine the current understanding of DHA.

RESULTS

Three cases of DHA were diagnosed based on bleeding phenotype: 2 cases represented missed diagnoses of HA, and 1 represented misclassification of hemophilia severity. The revised diagnosis and classification of hemophilia directly affected clinical management. Review of the literature identified 18 articles with an estimated pooled prevalence of 36% (95% CI, 23%-56%; I2 = 85%; P < .01) among nonsevere HA. Furthermore, literature indicated that DHA is a feature of how different FVIII gene mutations affect FVIII:C activity within different assay methodologies.

CONCLUSIONS

Our experience and literature review suggested that DHA is not only a laboratory phenomenon-it can affect clinical management in a subset of patients. A high index of suspicion for DHA is necessary while evaluating bleeding patients and/or classifying nonsevere HA.

The European Association for Haemophilia and Allied Disorders (EAHAD) Coagulation Factor Variant Databases: Important resources for haemostasis clinicians and researchers

INTRODUCTION

Advances in genomic sequencing have facilitated the sequencing of genes associated with disorders of haemostasis. The identification of variants within genes and access to curated data incorporating structural, functional, evolutionary as well as phenotypic data has become increasingly important in order to ascribe pathogenicity.

AIM

The European Association for Haemophilia and Allied Disorders (EAHAD) Coagulation Factor Variant Database Project aims to provide a single port of entry to a web-accessible resource for variants in genes involved in clinical bleeding disorders.

RESULTS

New databases have evolved from previously developed single gene variant coagulation database projects, incorporating new data, new analysis tools and a new common database architecture with new interfaces and filters. These new databases currently present information about the genotype, phenotype (laboratory and clinical) and structural and functional effects of variants described in the genes of factor (F) VII (F7), FVIII (F8), FIX (F9) and von Willebrand factor (VWF).

CONCLUSION

The project has improved the quality and quantity of information available to the haemostasis research and clinical communities, thereby enabling accurate classification of disease severity in order to make assessments of likely pathogenicity.

Structural variations causing inherited peripheral neuropathies: A paradigm for understanding genomic organization, chromatin interactions, and gene dysregulation

Inherited peripheral neuropathies (IPNs) are a clinically and genetically heterogeneous group of diseases affecting the motor and sensory peripheral nerves. IPNs have benefited from gene discovery and genetic diagnosis using next-generation sequencing with over 80 causative genes available for testing. Despite this success, up to 50% of cases remain genetically unsolved. In the absence of protein coding mutations, noncoding DNA or structural variation (SV) mutations are a possible explanation. The most common IPN, Charcot-Marie-Tooth neuropathy type 1A (CMT1A), is caused by a 1.5 Mb duplication causing trisomy of the dosage sensitive gene PMP22. Using genome sequencing, we recently identified two large genomic rearrangements causing IPN subtypes X-linked CMT (CMTX3) and distal hereditary motor neuropathy (DHMN1), thereby expanding the spectrum of SV mutations causing IPN. Understanding how newly discovered SVs can cause IPN may serve as a useful paradigm to examine the role of topologically associated domains (TADs), chromatin interactions, and gene dysregulation in disease. This review will describe the growing role of SV in the pathogenesis of IPN and the importance of considering this type of mutation in Mendelian diseases where protein coding mutations cannot be identified.

Prenatal diagnosis of sex chromosomal inversion, translocation and deletion

The aim of the present study was to perform comprehensive prenatal diagnosis using various detection techniques on a fetus in a high‑risk pregnant woman, and to provide genetic counseling for the patient and her family so as to avoid birth defects. The routine karyotype analysis via amniocentesis, fluorescence in situ hybridization, and whole genome microarray technique were performed for the prenatal diagnosis of the fetus. The fetal karyotype was 46,X,ish der(X) inv(X)(p22.3q28)t(X;Y)(q28;q11.2)(XYqter+,SRY‑,DXZ1+, RP11‑64L19+,STS+,XYpter+); namely, one fetal X chromosome belonged to the derivative imbalanced chromosome and this chromosome demonstrated complex chromosomal rearrangements involving inversion, translocation and deletion. Notably, pericentric inversion between Xp22.3 and Xq28 was identified, and the chromosomal microarray technique confirmed that the long arm q28 of the derivative X chromosome had a 1.241‑Mb deletion in Xq28, which included Online Mendelian Inheritance in Man genes such as coagulation factor VIII, glucose‑6‑phosphate dehydrogenase, inhibitor of nuclear factor‑κB kinase subunit γ, trimethyllysine hydroxylase ε, Ras‑related protein Rab‑39B and chloride intracellular channel 2. In addition, this chromosome also exhibited the local translocation of fragment Yq11.21‑q11.23, which did not include the sex determining region Y gene. This fetus demonstrated deletion, inversion and translocation syndrome, and may exhibit the corresponding clinical phenotypes (e.g., intellectual disability or general delayed development) (1) of such chromosome abnormalities after birth. Therefore, in prenatal diagnosis, a variety of genetic diagnostic techniques should be comprehensively used based on specific clinical situations, which may accurately reveal the nature, sources and manifestations of the derivative chromosome abnormalities and avoid the birth of children with defects.

In silico analyses of missense mutations in coagulation factor VIII: identification of severity determinants of haemophilia A

Factor VIII (FVIII) mutations cause haemophilia A (HA), an X-linked recessive coagulation disorder. Over 1000 missense mutations in FVIII are known and they lead to variable clinical phenotypes (severe, moderate and mild). The exact molecular basis of this phenotypic heterogeneity by FVIII missense mutations is elusive to date. In this study, we aimed to identify the severity determinants that cause phenotypic heterogeneity of HA. We compiled and curated a data set of 766 missense mutations from the repertoire of missense mutations in FVIII. We analysed these mutations by computational programs (e.g. Swiss-PdbViewer) and different mutation analysis servers (e.g. SIFT, PROVEAN, CUPSAT, PolyPhen2, MutPred); and various sequence- and structure-based parameters were assessed for any significant distribution bias among different HA phenotypes. Our analyses suggest that 'mutations in evolutionary conserved residues', 'mutations in buried residues', mutation-induced 'steric clash' and 'surface electrostatic potential alteration' act as risk factors towards severe HA. We have developed a grading system for FVIII mutations combining the severity determinants, and the grading pattern correlates with HA phenotype. This study will help to correctly associate the HA phenotype with a mutation and aid early characterization of novel variants.

Factor VIII Antigen, Activity, and Mutations in Hemophilia A

Factor VIII (FVIII) activity, antigen, and its gene mutation in patients may give us some insight into structure-activity relationship and probable reason for its low level in a particular patient. A total of 53 cases with hemophilia A and 17 normal individuals were analyzed for

FVIII

C and

FVIII

Ag levels along with their blood groups to determine their cross-reacting material (CRM) status. In all, 37 cases (18 moderate and 19 mild) were found to have discordant CRM status. Missense mutations (Ala723ThrandLys439Ser) and protein truncating changes (Trp1854*andArg2326*) were observed in 2 each of these cases. Although 37 (70%) of the 53 had discordant antigen-activity ratio, majority of those mutations produced FVIII with low FVIII-specific activity. However, 4 (7.5%) of the 53 mutations produced higher specific activity of FVIII. It is possible that these mutations either produce a secretory defect or an increased metabolic turnover to account for the low levels of FVIII with these mutations.

Paradigms of sulfotransferase catalysis: the mechanism of SULT2A1

Human cytosolic sulfotransferases (SULTs) regulate the activities of thousands of signaling small molecules via transfer of the sulfuryl moiety (-SO3) from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to the hydroxyls and primary amines of acceptors. Sulfonation controls the affinities of ligands for their targets, and thereby regulates numerous receptors, which, in turn, regulate complex cellular responses. Despite their biological and medical relevance, basic SULT mechanism issues remain unresolved. To settle these issues, and to create an in-depth model of SULT catalysis, the complete kinetic mechanism of a representative member of the human SULT family, SULT2A1, was determined. The mechanism is composed of eight enzyme forms that interconvert via 22 rate constants, each of which was determined independently. The result is a complete quantitative description of the mechanism that accurately predicts complex enzymatic behavior. This is the first description of a SULT mechanism at this resolution, and it reveals numerous principles of SULT catalysis and resolves previously ambiguous issues. The structures and catalytic behaviors SULTs are highly conserved; hence, the mechanism presented here should prove paradigmatic for the family.

Genetic factors influencing inhibitor development in a cohort of South African haemophilia A patients

A critical complication of factor VIII (FVIII) replacement therapy in Haemophilia A (HA) treatment is inhibitor development. Known genetic factors predisposing to inhibitor development include FVIII (F8) gene mutations, ethnicity, a family history of inhibitors and FVIII haplotype mismatch. The aim of this study was to characterize and correlate these genetic factors in a cohort of South African HA patients. This was a retrospective study that included 229 patients and involved the analysis of patient files, HA molecular and clinical databases and molecular analysis of the F8 gene haplotype. Of the 229 patients, 51% were of black ethnicity, 49% were white, 5% had mild HA, 4% were moderate and 91% were severe, 36% were int22 positive and 13% were inhibitor positive. Of the inhibitor positive patients, 72% were black patients. Inhibitors were reported in 27% of black int22 positive patients, 13% of black int22 negative patients, 9% of white int22 positive patients and 7% of white int22 negative. The H1 haplotype was more common in whites (75%) and H2 was more common in blacks (74%). H3 and H5 were only found in black patients and had a higher frequency of inhibitor development than H1 and H2. In this small HA cohort, black patients had a significantly higher frequency of inhibitor development and the results were indicative of an association between inhibitor development, ethnicity and haplotype.

Modeling of hemophilia A using patient-specific induced pluripotent stem cells derived from urine cells

AIMS

Hemophilia A (HA) is a severe, congenital bleeding disorder caused by the deficiency of clotting factor VIII (FVIII). For years, traditional laboratory animals have been used to study HA and its therapies, although animal models may not entirely mirror the human pathophysiology. Human induced pluripotent stem cells (iPSCs) can undergo unlimited self-renewal and differentiate into all cell types. This study aims to generate hemophilia A (HA) patient-specific iPSCs that differentiate into disease-affected hepatocyte cells. These hepatocytes are potentially useful for in vitro disease modeling and provide an applicable cell source for autologous cell therapy after genetic correction.

MAIN METHODS

In this study, we mainly generated iPSCs from urine collected from HA patients with integration-free episomal vectors PEP4-EO2S-ET2K containing human genes OCT4, SOX2, SV40LT and KLF4, and differentiated these iPSCs into hepatocyte-like cells. We further identified the genetic phenotype of the FVIII genes and the FVIII activity in the patient-specific iPSC derived hepatic cells.

KEY FINDINGS

HA patient-specific iPSCs (HA-iPSCs) exhibited typical pluripotent properties evident by immunostaining, in vitro assays and in vivo assays. Importantly, we showed that HA-iPSCs could differentiate into functional hepatocyte-like cells and the HA-iPSC-derived hepatocytes failed to produce FVIII, but otherwise functioned normally, recapitulating the phenotype of HA disease in vitro.

SIGNIFICANCE

HA-iPSCs, particular those generated from the urine using a non-viral approach, provide an efficient way for modeling HA in vitro. Furthermore, HA-iPSCs and their derivatives serve as an invaluable cell source that can be used for gene and cell therapy in regenerative medicine.

HindIII-based restriction fragment length polymorphism in hemophilic and nonhemophilic patients

Hemophilia A is most common recessively inherited bleeding disorder, which affect one in five thousand male births throughout the world. In most of the hemophilic A patients, no common mutation is easily identifiable. This limitation has been overcome by the use of polymorphic DNA marker, i.e., restriction fragment length polymorphism (RFLP). This marker of polymorphism could only be detected by amplifying the polymorphic region and digestion the polymerase chain reaction (PCR) product with the restriction enzyme (PCR−RFLP), i.e., HindIII. The polymorphic region of HindIII is 608 bp in length and after the restriction digestion, different sizes of fragments, i.e., 427 and 181 bp were, respectively, obtained. However, in homozygous (+/+) condition three bands of 427, 100, and 81 bp were obtained and in the other negative allelic homozygous condition (-/-) two bands of 427 and 181 bp were obtained. Similarly fragments of different sizes, i.e., 427, 181, 100, and 81 bp were obtained in heterozygous conditions. Therefore, in this study, we have analyzed the factor VIII gene in the 17 different families using restriction enzyme HindIII-based RFLP molecular marker technique. Out of these, the observed heterozygosity for HindIII was found 47.5%, whereas, for positive allele it was 26%, and for negative allele the frequency was 74%.

Identification of FVIII gene mutations in patients with hemophilia A using new combinatorial sequencing by hybridization

BACKGROUND:

Standard methods of mutation detection are time consuming in Hemophilia A (HA) rendering their application unavailable in some analysis such as prenatal diagnosis.

OBJECTIVES:

To evaluate the feasibility of combinatorial sequencing-by-hybridization (cSBH) as an alternative and reliable tool for mutation detection in FVIII gene.

PATIENTS/METHODS:

We have applied a new method of cSBH that uses two different colors for detection of multiple point mutations in the FVIII gene. The 26 exons encompassing the HA gene were analyzed in 7 newly diagnosed Italian patients and in 19 previously characterized individuals with FVIII deficiency.

RESULTS:

Data show that, when solution-phase TAMRA and QUASAR labeled 5-mer oligonucleotide sets mixed with unlabeled target PCR templates are co-hybridized in the presence of DNA ligase to universal 6-mer oligonucleotide probe-based arrays, a number of mutations can be successfully detected. The technique was reliable also in identifying a mutant FVIII allele in an obligate heterozygote. A novel missense mutation (Leu1843Thr) in exon 16 and three novel neutral polymorphisms are presented with an updated protocol for 2-color cSBH.

CONCLUSIONS:

cSBH is a reliable tool for mutation detection in FVIII gene and may represent a complementary method for the genetic screening of HA patients.

Genotype-phenotype correlation in MYH9-related thrombocytopenia

Mutation of the non-muscle myosin heavy chain type II-A results in MYH9-related hereditary macrothrombocytopenia (HMTC), including four autosomal dominant platelet disorders: May-Hegglin anomaly (MHA), Sebastian (SBS), Fechtner (FS) and Epstein (EPS) syndrome. Denaturing high-performance liquid chromatography (DHPLC) was optimised for rapid screening of the seven exons harbouring all but one of the previously reported mutations of MYH9. Individuals from 13 families with phenotypes suggestive of MYH9-related HMTC were screened for mutations by DHPLC followed by direct sequencing of samples with aberrant column retention time. Mutations were identified in all 13 families. Six distinct missense heterozygous mutations were found in 10 families, including six families with MHA or SBS (E1841K, D1424N), three families with FS (R702H, R1165C, and D1424Y), and one family with EPS (S96L). A truncating mutation (R1933X) was found in three MHA families. A review of all published mutations suggests that mutation in the C-terminal coiled coil region or truncation of the tailpiece is associated with haematological-only phenotype, while mutation of the head ATPase domain frequently is associated with nephropathy and/or hearing loss. Mutations of other regions have intermediate expression of non-haematological characteristics. Further study is required to confirm these associations and understand the molecular basis for this genotype-phenotype relationship.

Polymorphism distribution of Int13, Int22, and St14 VNTRs in a Mexican population and their application in carrier diagnosis of hemophilia A

Variable nucleotide tandem repeats (VNTR) Int13, Int22, and St14 were analyzed to determine polymorphic distribution in normal individuals from Mexico's central region and their efficacy in detecting hemophilia A carriers. Polymerase chain reaction (PCR) was carried out on 166 X chromosomes from unrelated Mexicans, and the same method was applied to detect carriers in hemophilia A families. Screening revealed the existence of at least eight different alleles for Int13, 4 alleles for Int22, and 10 alleles for St14. Their heterozygosity rates were 41.3%, 52.6%, and 83%, respectively. Compared to Caucasians, the Mexican population showed a markedly low heterozygosity rate for the Int13 marker. However, Int22 showed a heterozygosity that was similar to Turkish and Chinese populations. The St14 marker was the most informative in carrier diagnosis, and a new 680-bp allele not previously reported was detected. Carrier diagnosis was performed in 39 women from eight different hemophilia A families. Fifteen (38%) females were not carriers, 16 (41%) females were carriers, and 8 (21%) were homozygous. Determination of polymorphisms in VNTR markers revealed that St14 was the most useful for hemophilia A carrier detection in Mexico.

Genetic analysis of haemophilia A in Bulgaria

BACKGROUND

Haemophilias are the most common hereditary severe disorders of blood clotting. In families afflicted with heamophilia, genetic analysis provides opportunities to prevent recurrence of the disease. This study establishes a diagnostical strategy for carriership determination and prenatal diagnostics of haemophilia A in Bulgarian haemophilic population.

METHODS

A diagnostical strategy consisting of screening for most common mutations in the factor VIII gene and analysis of a panel of eight linked to the factor VIII gene locus polymorphisms was established.

RESULTS

Polymorphic analysis for carrier status determination of haemophilia A was successful in 30 families out of 32 (94%). Carrier status was determined in 25 of a total of 28 women at risk (89%). Fourteen prenatal diagnoses in women at high risk of having a haemophilia A - affected child were performed, resulting in 6 healthy boys and 5 girls.

CONCLUSION

The compound approach proves to be a highly informative and cost-effective strategy for prevention of recurrence of haemophilia A in Bulgaria. DNA analysis facilitates carriership determination and subsequent prenatal diagnosis in the majority of Bulgarian families affected by haemophilia A.

Blood coagulation factor VIII: An overview

Factor VIII (FVIII) functions as a co-factor in the blood coagulation cascade for the proteolytic activation of factor X by factor IXa. Deficiency of FVIII causes hemophilia A, the most commonly inherited bleeding disorder. This review highlights current knowledge on selected aspects of FVIII in which both the scientist and the clinician should be interested.

Temporal and spatial expression of biologically active human factor VIII in the milk of transgenic mice driven by mammary-specific bovine alpha-lactalbumin regulation sequences

Hemophilia A is one of the major inherited bleeding disorders caused by a deficiency or abnormality in coagulation factor VIII (FVIII). Hemophiliacs have been treated with whole plasma or purified FVIII concentrates. The risk of transmitting blood-borne viruses and the cost of highly purified FVIII are the major factors that restrict prophylaxis in hemophilia therapy. One of the challenges created by the biotechnology revolution is the development of methods for the economical production of highly purified proteins in large scales. Recent developments indicate that manipulating milk composition using transgenesis has focused mainly on the mammary gland as a bioreactor to produce pharmaceuticals. In the present study, a hybrid gene containing bovine alpha-lactalbumin and human FVIII cDNA was constructed for microinjection into the pronuclei of newly fertilized mouse eggs. The alphaLA-hFVIII hybrid gene was confirmed to be successfully integrated and stably germ-line transmitted in 12 (seven females/five males) lines. Western-blot analysis of milk samples obtained from eight of the transgenic founders and F1 offspring indicated that the recombinant hFVIII was secreted into the milk of the transgenic mice. The concentrations of rFVIII ranged from 7.0 to 50.2 microg/ml, over 35-200-fold higher than that in normal human plasma. Up to 13.4 U/ml of rFVIII was detected in an assay in which rFVIII restored normal clotting activity to FVIII-deficient human plasma.

In hemophilia A and autoantibody inhibitor patients: the factor VIII A2 domain and light chain are most immunogenic

Factor VIII (fVIII) is a protein cofactor essential for blood coagulation, and it binds in the factor Xase complex to factors IXa, X, and phospholipid. In about 30% of severe hemophilia A patients, treatment with fVIII leads to production of anti-fVIII antibodies. Anti-fVIII autoantibodies also rarely appear in normal individuals. Those antibodies that inactivate fVIII (inhibitors) prevent optimal fVIII therapy. Inhibitor epitopes were previously localized to the fVIII A2, A3, and C2 domains and to an acidic amino acid region between A1 and A2. Such anti-fVIII antibodies interfere with fVIII binding to components of the factor Xase complex and prevent blood coagulation. When total anti-fVIII titers were determined for each fVIII domain in 43 inhibitor plasmas by immunoprecipitation (IP) and inhibitor neutralization assays, the anti-light chain (LCh) antibody titer was highest, anti-A2 was intermediate, and anti-A1 and anti-B were low. The relative immunogenicity of the fVIII domains in hemophilic and autoantibody inhibitor patients was similar.

Haemophilias: advances towards genetic engineering replacement therapy

Both haemophilia A and B are X-linked recessive disorders and therefore occur almost exclusively in males. The genes for both factors VIII and IX have been mapped to the distal end of the long arm of the X chromosome, bands Xq28 and Xq27.1, respectively. The Factor VIII gene comprises 186 kb DNA with 9 kb of exon of DNA which encodes an mRNA of nearly 9 kb. The Factor IX gene is 34 kb in length and the essential genetic information is present in eight exons which encode 1.6 kb mRNA. In gene therapy, genetic modification of the target cells can be either ex vivo or in vivo. The advantage of the ex vivo approach is that the genetic modification is strictly limited to the isolated cells. In the in vivo approach, the integrity of the target tissue is maintained but the major challenge is to deliver the gene to the target tissue. The use of improved retroviral and adenovirus-based vectors for gene therapy has produced clinically relevant levels of human factor VIII in mice and haemophilic dogs. If further improvements can increase the persistence of expression and decrease the immunological responses, phase I clinical trials in patients can be considered.

Ionizing radiation and genetic risks. XII. The concept of "potential recoverability correction factor" (PRCF) and its use for predicting the risk of radiation-inducible genetic disease in human live births

Genetic risks of radiation exposure of humans are generally expressed as expected increases in the frequencies of genetic diseases over those that occur naturally in the population as a result of spontaneous mutations. Since human data on radiation-induced germ cell mutations and genetic diseases remain scanty, the rates derived from the induced frequencies of mutations in mouse genes are used for this purpose. Such an extrapolation from mouse data to the risk of genetic diseases will be valid only if the average rates of inducible mutations in human genes of interest and the average rates of induced mutations in mice are similar. Advances in knowledge of human genetic diseases and in molecular studies of radiation-induced mutations in experimental systems now question the validity of the above extrapolation. In fact, they (i) support the view that only in a limited number of genes in the human genome, induced mutations may be compatible with viability and hence recoverable in live births and (ii) suggest that the average rate of induced mutations in human genes of interest from the disease point of view will be lower than that assumed from mouse results. Since, at present, there is no alternative to the use of mouse data on induced mutation rates, there is a need to bridge the gap between these and the risk of potentially inducible genetic diseases in human live births. In this paper, we advance the concept of what we refer to here as "the potential recoverability correction factor" (PRCF) to bridge the above gap in risk estimation and present a method to estimate PRCF. In developing the concept of PRCF, we first used the available information on radiation-induced mutations recovered in experimental studies to define some criteria for assessing potential recoverability of induced mutations and then applied these to human genes on a gene-by-gene basis. The analysis permitted us to estimate unweighted PRCFs (i.e. the fraction of genes among the total studied that might contribute to recoverable induced mutations) and weighted PRCFs (i.e. PRCFs weighted by the incidences of the respective diseases). The estimates are: 0.15 (weighted) to 0.30 (unweighted) for autosomal dominant and X-linked diseases and 0.02 (weighted) to 0.09 (unweighted) for chronic multifactorial diseases. The PRCF calculations are unnecessary for autosomal recessive diseases since the risks projected for the first few generations even without using PRCFs are already very small. For congenital abnormalities, PRCFs cannot be reliably estimated. With the incorporation of PRCF into the equation used for predicting risk, the risk per unit dose becomes the product of four quantities (risk per unit dose=Px(1/DD)xMCxPRCF) where P is the baseline frequency of the genetic disease, 1/DD is the relative mutation risk per unit dose, MC is the mutation component and PRCF is the disease-class-specific potential recoverability correction factor instead of the first three (as has been the case thus far). Since PRCF is a fraction, it is obvious that the estimate of risk obtained with the revised risk equation will be smaller than previously calculated values.

Adenoviral vector-mediated expression of physiologic levels of human factor VIII in nonhuman primates

An E1-, E2a-, E3-deleted adenoviral vector (Av3H82) encoding an epitope-tagged B domain-deleted human factor VIII cDNA (flagged FVIII) was evaluated in nonhuman primates. Twelve cynomolgus monkeys received intravenous administration of Av3H82; 6 monkeys received 6 x 10(11) particles/kg and another 6 received 3 x 10(12) particles/kg. Adenoviral vector transduction of the liver was efficient, reproducible, and linearly dose dependent. Physiologic levels of flagged FVIII were readily detected in plasma samples obtained from monkeys that received the higher dose of vector and human FVIII mRNA was detected in their livers. Expression of transgene mRNA was restricted to the liver by the albumin promoter. Although vector DNA was readily detected in the liver of monkeys that received the lower dose, neither human FVIII mRNA nor flagged FVIII protein could be detected. Vector distribution was widespread, with the highest levels observed in liver and spleen. Histopathology, hematology, and serum chemistry analysis identified the liver and blood as major sites of toxicity. Transient mild serum elevations of liver enzymes were observed, along with a dose-dependent inflammatory response in the liver. In addition, mild lymphoid hyperplasia was observed in the spleen. Mild anemia and a transient decrease in platelet count were observed, as was marrow hyperplasia and extramedullary hematopoiesis.

Expression of human blood clotting factor VIII in the mammary gland of transgenic sheep

By targeting the expression of sequences encoding non-milk proteins to the mammary gland of transgenic farm animals, the organ could serve as a 'bioreactor' for producing pharmacologically active proteins on a large scale. Here we report the generation of transgenic sheep bearing a fusion gene construct with the human blood clotting factor VIII (hFVIII) cDNA under the transcriptional control of a 2.2 kb fragment of the mammary gland specific promoter of the ovine beta-Lactoglobulin (beta-Lac) gene. Six founder animals were generated bearing a hFVIII cDNA construct with the introns of the murine metallothionein (MtI) gene (beta-Lac/hFVIII-MtI). Founders transmitted the transgene in a Mendelian fashion and two transgenic lines were generated. Ten out of 12 transgenic F1-females expressed rhFVIII mRNA in exfoliated mammary epithelial cells isolated from the milk. But only in transgenic F1 ewes 4010 and 603 hFVIII clotting activity estimated at 4-6 ng/ml was detected in defatted milk. Furthermore, the presence of rhFVIII-protein in ovine milk was demonstrated by a specific band at approximately 190 kD following immunoprecipitation and immunoblotting. Transgenic founder 395 expressed rhFVIII mRNA in biopsied mammary gland tissue, in exfoliated mammary cells as well as ectopically in brain, heart, spleen, kidney and salivary gland, suggesting that the employed beta-Lac promoter fragment lacks essential sequences for directing expression exclusively to the mammary gland. A rhFVIII standard preparation (rhFVIIIstd) was rapidly sequestered in a saturable fashion in ovine milk, thus rendering it largely inaccessible to immunoprecipitation although its biological activity was retained. Recovery of hFVIIIstd was dependent on milk donor, storage temperature and dilution of milk sample.

Expression of transposon LINE-1 is relatively human-specific and function of the transcripts may be proliferation-essential

A new 1.7-kb LINE (L1) transcript has been discovered from the cDNA library of human small-cell lung cancer. The nucleotide sequence of 1.7-kb L1 transcript is 98.4% similar to that of open reading frame 2 (ORF2) found in consensus complete 6.5-kb L1. Although L1 DNA segments could be detected from both genomic DNAs of human and rodent cells by PCR, these L1 transcripts were not detectable from cellular RNA of rodent cells by RT-PCR and northern hybridization, implying that the expression of L1 was relatively human-specific. The functions of L1 transcripts in cells are not yet clear. This paper shows that L1 transcripts are essential for cell proliferation when determined by antisense oligonucleotides. Alternately, L1 transcripts exhibit in all human cells we have examined so far, and they map to all the human chromosomes. A sequence-similarity search in the GenBank database indicates that the major sequence of 1.7-kb L1 is integrated in human retinoblastoma (Rb), IL-2, and factor VIII genes. Since Rb and factor VIII genes have displayed high frequency of chromosomal deletions in various cancers and haemophilia A, the universal integration of long and homologous L1 segments in the genes and all chromosomes may be liable to promote abnormal DNA rearrangement.

Hemophilia. A new approach to an old disease

The history of hemophilia diagnosis and therapy has been a turbulent one. We are coming full circle, back to the use of genetics as the main diagnostic tool for this disease. Therapeutically, the retroviruses that ravaged one generation of hemophiliac patients now may participate in the cure for the next generation. The hemophilia community hopes that the future of hemophilia care will follow a course guided by this modified quote from James Russell Lowell: "New times demand new measures, and men [and women]. As the world advances and in time outgrows the laws that in our fathers' [and mothers'] days were the best, doubtless after us some purer scheme will be shaped out by wiser man [and women] than we, made wiser by the steady growth of truth."

Genetic Counseling by Analysis of Intron 22 Inversions of the Factor VIII Gene

Ten patients with severe hemophilia A and 10 with moderate and mild hemophilia A were studied. Five of 10 unrelated patients with severe hemophilia A had the distal telo meric int22h sequence, none had the proximal sequence, and one had a unique variant factor VIII gene rearrangement. Car rier detection was done in these six families. All mothers and two daughters of the patients were to be carriers. Six of the 15 at-risk female relatives were heterozygous for the rearranged and normal allele and were carriers. These results indicate that the rearrangement assay is very useful for carrier detection in families with severe hemophilia A. Key Words: Hemophilia A—Factor VIII gene rearrangement—Genetic counseling.

A Non-Sense Mutation at Arg95 Is Predominant in Complement 9 Deficiency in Japanese

Deficiency of the ninth component of complement (C9D) is one of the most common genetic abnormalities in Japan, with an incidence of one homozygote in 1000. Although C9D individuals are usually healthy, it has been shown that they have an significantly increased risk of developing meningococcal meningitis. In the present study we report the molecular bases for C9D in 10 unrelated Japanese subjects. As a screening step for mutations, exons 2 to 11 of the C9 gene were analyzed using exon-specific PCR/single-strand conformation polymorphism analysis, which demonstrated aberrantly migrating DNA bands in exon 4 in all the C9D subjects. Subsequent direct sequencing of exon 4 of the C9D subjects revealed that eight of the 10 C9D subjects were homozygous for a C to T transition at nucleotide 343, the first nucleotide of the codon CGA for Arg95, leading to a TGA stop codon (R95X). R95X is a novel mutation different from those recently identified in a Swiss family with C9D. Cases 6 and 7 were heterozygous for the R95X mutation. Family study in case 10 confirmed the genetic nature of the defect. In case 6, the second mutation for C9D of the C9 gene was identified to be the substitution of Cys to Tyr at amino acid residue 507 (C507Y), while the genetic defect(s) in the other allele in case 7 remains unknown. Our results indicate that a novel mutation, R95X, is present in most cases of C9D in Japan.

The factor VIII Structure and Mutation Resource Site: HAMSTeRS version 4

Since 1996 the HAMSTeRS (Haemophilia A Mutation, Search, Test and Resource Site) WWW site has provided an online resource for access to data on the molecular pathology of haemophilia A, replacing previous text editions of the Haemophilia A Database published in Nucleic Acids Research . This report describes the continued development of the site (version 4), and in particular the expansion of factor VIII (FVIII) structure-related features. Access to the mutation database itself, both for searching the listings and for submission of new mutations, is via custom-designed forms: more powerful Boolean searches of the point mutations in the database are also available. During 1997 a total of 22 novel missense mutations were reported, increasing the total number of unique variants now described to 252 (238 in exonic sequences and 14 at intronic splice junctions). Currently, a total of 586 individual reports with associated phenotypic data are available for searching by any category including phenotype. The FVIII structure section now includes a download of a FVIII A domain homology model in Protein Data Bank format and a multiple alignment of the FVIII amino-acid sequencies from four species (human, murine, porcine and canine) in addition to the virtual reality simulations, secondary structural data and FVIII animation already available. Finally, to aid navigation across this site, a clickable roadmap of the main features provides easy access to the page desired. Our intention is that continued development and updating of the site shall provide workers in the fields of molecular and structural biology with a one-stop resource site to facilitate FVIII research and education. The HAMSTeRS URL is http://europium.mrc.rpms.ac.uk

Gene therapy for the hemophilias

There are many lines of evidence that suggest the eventual success of gene therapy as a treatment strategy for hemophilia. Because current treatment protocols using plasma-derived or recombinant proteins are far from ideal, the safe and efficient substitution of the defective gene by a normal copy of the gene, or at least its addition, would be of great benefit to the patient and may even be a potential cure. However, the construction of efficient gene therapy vehicles has proven quite difficult in the past and, so far, there is no system that promises to have all the desired features without any serious disadvantages. In general, either the levels of transgene expression are too low (because of the low titers achieved during the generation of the virus) or shortlived (e.g., because of the specific shut-off of the transferred promoter) as is often seen with retroviruses, or in the case of adenoviral vectors, expression is limited because of a strong immune response of the host. Clearly, much work remains to be done to optimize these promising though still imperfect vector systems. In the case of adenovirus, the development of less immunogenic vectors or in vivo modulation of the host immune system may hold promise for improvements. Reports by Yang et al. (1995) and Kay et al. (1995) are promising steps in the direction of immunomodulation. Both attenuate the immune reaction to the adenoviral vector by simultaneous application of either an interleukin or an immunoglobulin, respectively. When IL-2 was administered, the amounts of IgA were reduced and successful administration of a second dose of virus was possible. When CTLA4-Ig, an immunoglobulin that blocks the second signal during antigen presentation, was administered, a markedly prolonged expression of the transgene resulted. In vivo trials with AAV vectors have been carried out for some diseases (Flotte et al., 1993; Kaplitt et al., 1994) but not for hemophilia. Advances in high-titer AAV vector preparation will make this approach more feasible. The pace continues to quicken in the development of nonviral modes of gene delivery (Perales et al., 1994). Although these results are encouraging for the future of gene therapy as a treatment for genetic diseases, much work remains to be done to make this potential alternative a reality for treatment of hemophilia.

Rapid polymerase chain reaction analysis of St14 (DXS52) VNTR: carrier detection of hemophilia A

OBJECTIVE

To determine the frequency of St14 VNTR allele in Koreans as a marker of the hemophilia A and to evaluate the efficacy of this marker for carrier detection of hemophilia A METHODS: PCR amplified RFLP analysis of St14 VNTR was done in 312 X-chromosomes of 122 unrelated Korean males and 95 females and the same method was applied to carrier detection in the 2 hemophilia A families.

RESULTS

There were 13 alleles of different sizes of St14 VNTR locus appeared in 312 X-chromosomes of unrelated Koreans. For carrier detection of hemophilia A, in the family A, the mother showed 1390/ 1330 bp alleles and the father showed 700 bp allele. The affected son has inherited 1390 bp allele from his mother. The daughter at risk showed 1330/700 bp alleles. In family B, the mother showed 1280/700 bp alleles and the stepfather showed 1390 bp allele. The affected son has inherited 1280 bp allele. The daughter at risk showed 1390/700 bp alleles. And so the daughters of the 2 families were not carriers for hemophilia A.

CONCLUSION

PCR analysis of St14 VNTR was a useful tool for carrier detection of hemophilia A.

Haemophilia

Although the nature of haemophilia has been understood for thousands of years, knowledge of its molecular genetics is recent. These X-linked bleeding disorders have diverse underlying DNA defects and, in 1992, DNA inversion within the X chromosome was found to explain half of the most serious cases of haemophilia A. The life-span and quality-of-life for patients with haemophilia had improved steadily throughout the early 1980s but the principal cause of death remained intracranial haemorrhage until the epidemic of HIV infection due to contaminated factor concentrates. Infection with hepatitis C virus is almost universal for patients treated with clotting factors before 1985. No curative treatment is available for hepatitis C at present. Knowledge of the transmission of viruses in concentrates has led to important developments in processing techniques to eliminate them. Recombinant technology has produced factor VIII and, more recently, factor IX concentrate which is likely to be very safe. Development of inhibitors to factor concentrates (especially factor VIII) remains one of the most serious complications of haemophilia. The variety of treatments available testifies to the lack of a single universally efficacious one. The use of prophylactic treatment has been conclusively demonstrated to result in a preservation of joint function in severely affected patients who might otherwise develop significant joint problems. The many facets of the care of patients with severe haemophilia, ranging from dental care to genetic counselling, can be advantageously co-ordinated in a haemophilia comprehensive care centre.

Studies to detect carriers of haemophilia A in German shepherd dogs using diagnostic DNA polymorphisms in the human factor VIII gene

The current study investigated whether the DNA polymorphisms in the human FVIII gene, that are used for the diagnosis of carriers of haemophilia A, were diagnostically useful in dogs. Genomic DNA from 20 German Shepherd dogs (13 females, three normal males and four haemophilic males) was tested using five restriction site polymorphisms [HindIII/F8 (exon 17-18), Taq I/ST14.1, BclI/ST14.1, BclI F8 (exon 17-18) and Bgl II/DX13]. The DNA probes (with the exception of DX13) all hybridized to the canine DNA at high stringency, indicating significant homology between the human and canine FVIII gene. A BclI polymorphism (13.5/13.5 + 12.8 kb) was detected with the ST14.1 probe.

Identification of novel factor VIII inhibitor epitopes using synthetic peptide arrays

OBJECTIVES

Mapping the antibody-binding sites on the factor VIII (FVIII) protein opens the prospect of studying the development of FVIII inhibitors and the alteration of inhibitor specificities over time. This paper describes a novel approach to the mapping of FVIII antibody-binding sites.

METHODS

Immobilized synthetic peptide arrays covering 80% of the complete 2351 amino acid sequence of factor VIII (FVIII) were used to determine epitope specificity of 6 alloantibodies and 3 autoantibodies inhibitory to FVIII activity. This detailed assessment was carried out using a modified enzyme-linked immunosorbent assay with plasma from normal persons or hemophilia A patients without inhibitors as negative controls.

RESULTS

Antibody-combining sites could be differentiated in both a qualitative and quantitative manner and were patient-specific. Highly reactive peptides were restricted to specific sites in the A1-A3 and C1-C2 domains and were not proximal to known proteolytic cleavage sites. Free peptides incubated in vitro with the plasmas of 3 patients significantly reduced residual inhibitor titers in a dose-dependent manner.

CONCLUSION

This technique permits the study of the development and specificity of FVIII inhibitors, can detect and differentiate between inhibitory and noninhibitory antibodies using immobilized or free peptides respectively, permits correlation of antibody-combining sites with inhibition of FVIII activity and provides a basis for the development of inhibitor adsorption or neutralization technology.

Current Practice in the Treatment of Haemophilia

Haematologists are long standing proponents of evidence based practice-well exemplified among professionals who care for patients with haemophilia. The rapidly expanding range of therapeutic products and the numerous accompanying clinical trials are swiftly interpreted and translated into clinical practice. This translation is formalised by frequently updated quidelines issued by the United Kingdom Haemophilia Centre Directors' Organisation (UKHCDO) and relevant to all doctors involved in the care of patients with haemophilia. In the last five years eight sets of guidelines have been issued in the UK alone relating to the treatment of haemophilia and its complications [1-8]. Against this background we aim to review current practice in the treatment of haemophilia.

The human clotting factor VIII cDNA contains an autonomously replicating sequence consensus- and matrix attachment region-like sequence that binds a nuclear factor, represses heterologous gene expression, and mediates the transcriptional effects of sodium butyrate

Expression of the human blood-clotting factor VIII (FVIII) cDNA is hampered by the presence of sequences located in the coding region that repress transcription. We have previously identified a 305-bp fragment within the FVIII cDNA that is involved in the repression (R.C. Hoeben, F.J. Fallaux, S.J. Cramer, D.J.M. van den Wollenberg, H. van Ormondt, E. Briet, and A.J. van der Eb, Blood 85:2447-2454, 1995). Here, we show that this 305-bp region of FVIII cDNA contains sequences that resemble the yeast (Saccharomyces cerevisiae) autonomously replicating sequence consensus. Two of these DNA elements coincide with AT-rich sequences that are often found in matrix attachment regions or scaffold-attached regions. One of these elements, consisting of nucleotides 1569 to 1600 of the FVIII cDNA (nucleotide numbering is according to the system of Wood et al. (W.I. Wood, D.J. Capon, C.C. Simonsen, D.L. Eaton, J. Gitschier, D. Keyt, P.H. Seeburg, D.H. Smith, P. Hollingshead, K.L. Wion, et al., Nature [London] 312:330-337,1984), binds a nuclear factor in vitro but loses this capacity after four of its base pairs have been changed. A synthetic heptamer of this segment can repress the expression of a chloramphenicol acetyltransferase (CAT) reporter gene and also loses this capacity upon mutation. Furthermore, we demonstrate that repression by FVIII sequences can be relieved by sodium butyrate. We demonstrate that the synthetic heptamer (FVIII nucleotides 1569 to 1600), when placed upstream of the Moloney murine leukemia virus long terminal repeat promoter that drives the CAT reporter, can render the CAT reporter inducible by butyrate. This effect was absent when the same element was mutated. The stimulatory effect of butyrate could not be attributed to butyrate-responsive elements in the studied long terminal repeat promoters. Our data provide a functional characterization of the sequences that repress expression of the FVIII cDNA. These data also suggest a link between transcriptional repression by FVIII cDNA elements and the stimulatory effect of butyrate on FVIII cDNA expression.

Hemophilia 1996. New approach to an old disease

The history of hemophilia diagnosis and therapy has been a turbulent one. We are coming full circle, back to the use of genetics as the main diagnostic tool for this disease. Therapeutically, the retroviruses that ravaged one generation of hemophiliac patients now may participate in the cure for the next generation. The hemophilia community hopes that the future of hemophilia care will follow a course guided by this modified quote from James Russell Lowell: "New times demand new measures, and men [and women]. As the world advances and in time outgrows the laws that in our fathers' [and mothers'] days were the best, doubtless after us some purer scheme will be shaped out by wiser men [and women] than we, made wiser by the steady growth of truth."

Characterization of the factor VIII defect in 147 patients with sporadic hemophilia A: family studies indicate a mutation type-dependent sex ratio of mutation frequencies

The clinical manifestation of hemophilia A is caused by a wide range of different mutations. In this study the factor VIII genes of 147 severe hemophilia A patients--all exclusively from sporadic families--were screened for mutations by use of the complete panel of modern DNA techniques. The pathogenous defect could be characterized in 126 patients (85.7 percent). Fifty-five patients (37.4 percent) showed a F8A-gene inversion, 47 (32.0 percent) a point mutation, 14 (9.5 percent) a small deletion, 8 (5.4 percent) a large deletion, and 2 (1.4 percent) a small insertion. Further, four (2.7 percent) mutations were localized but could not be sequenced yet. No mutation could be identified in 17 patients (11.6 percent). Sixteen (10.9 percent) of the identified mutations occurred in the B domain. Four of these were located in an adenosine nucleotide stretch at codon 1192, indicating a mutation hotspot. Somatic mosaicisms were detected in 3 (3.9 percent) of 76 patients, mothers, comprising 3 of 16 de novo mutations in the patients mothers. Investigation of family relatives allowed detection of a de novo mutation in 16 of 76 two-generation and 28 of 34 three-generation families. On the basis of these data, the male:female ratio of mutation frequencies (k) was estimated as k = 3.6. By use of the quotients of mutation origin in maternal grandfather to patients mother or to maternal grandmother, k was directly estimated as k = 15 and k = 7.5, respectively. Considering each mutation type separately, we revealed a mutation type-specific sex ratio of mutation frequencies. Point mutations showed a 5-to-10-fold-higher and inversions a >10-fold-higher mutation rate in male germ cells, whereas deletions showed a >5-fold-higher mutation rate in female germ cells. Consequently, and in accordance with the data of other diseases like Duchenne muscular dystrophy, our results indicate that at least for X-chromosomal disorders the male:female mutation rate of a disease is determined by its proportion of the different mutation types.

A trinucleotide deletion together with a base duplication event at codon 439 in the human tyrosinase gene identifies a mutational hotspot

Molecular analysis of the human tyrosinase gene in two patients suffering from a temperature-sensitive form of albinism has identified a thymine triplet deletion at codon 439 which is accompanied by a duplication of the immediately preceding cytosine residue. This results in a two base pair frame shift leading to premature termination at codon 448, giving a truncated protein. Its relationship to other mutations in tyrosinase and the possible cause are discussed. The temperature-sensitive phenotype is due to the guanine to adenine mutation at codon 422, known to generate a temperature-sensitive enzyme. The CTTT at F439 in tyrosinase is also present at F508 in CFTR, the main mutation causing cystic fibrosis.

Structure-function relationship of bacterial prolipoprotein diacylglyceryl transferase: functionally significant conserved regions

The structure-function relationship of bacterial prolipoprotein diacylgyceryl transferase (LGT) Has been investigated by a comparison of the primary structures of this enzyme in phylogenetically distant bacterial species, analysis of the sequences of mutant enzymes, and specific chemical modification of the Escherichia coli enzyme. A clone containing the gene for LGT, lgt, of the gram-positive species Staphylococcus aureus was isolated by complementation of the temperature-sensitive lgt mutant of E. coli (strain SK634) defective in LGT activity. In vivo and in vitro assays for prolipoprotein diacylglyceryl modification activity indicated that the complementing clone restored the prolipoprotein modification activity in the mutant strain. Sequence determination of the insert DNA revealed an open reading frame of 837 bp encoding a protein of 279 amino acids with a calculated molecular mass of 31.6 kDa. S. aureus LGT showed 24% identity and 47% similarity with E. coli, Salmonella typhimurium, and Haemophilus influenzae LGT.S. aureus LGT, while 12 amino acids shorter than the E. coli enzyme, had a hydropathic profile and a predicted pI (10.4) similar to those of the E. coli enzyme. Multiple sequence alignment among E. coli, S. typhimurium, H. influenzae, and S. aureus LGT proteins revealed regions of highly conserved amino acid sequences throughout the molecule. Three independent lgt mutant alleles from E. coli SK634, SK635, and SK636 and one lgt allele from S. typhimurium SE5221, all defective in LGT activity at the nonpermissive temperature, were cloned by PCR and sequenced. The mutant alleles were found to contain a single base alteration resulting in the substitution of a conserved amino acid. The longest set of identical amino acids without any gap was H-103-GGLIG-108 in LGT from these four microorganisms. In E. coli lgt mutant SK634, Gly-104 in this region was mutated to Ser, and the mutant organism was temperature sensitive in growth and exhibited low LGT activity in vitro. Diethylpyrocarbonate inactivated the E. coli LGT with a second-order rate constant of 18.6 M-1S-1, and the inactivation of LGT activity was reversed by hydroxylamine at pH 7. The inactivation kinetics were consistent with the modification of a single residue, His or Tyr, essential for LGT activity.

Genetic diagnosis of haemophilia A of Chinese origin

Genetic diagnosis of haemophilia A has been studied in two aspects. One is to directly identify the mutations in the factor VIII genes of the affected probands, and the other is to examine the usefulness of several intragenic factor VIII markers for gene tracking. Direct mutational analysis by PCR-SSCP (polymerase chain reaction--single-strand conformation polymorphism) has been accomplished previously in 87 haemophilia A patients, accounting for nearly 10% of cases in Taiwan. Of the 87 cases, 46% were with point mutations, short deletions or insertions, and most of the remaining were with gene inversion readily identified by Southern blotting. Further examination of 112 patients has estimated a 33% incidence for gene inversion in all the patients with haemophilia A, or 37% in severe cases. Since the direct mutational detection described above cannot be used in all Chinese families with haemophilia A, genetic markers were also investigated. The two CA repeat markers located at intron 13 (CA-13) and intron 22 (CA-22), respectively, were amplified and analysed simultaneously. Seven different alleles with 18-24 CAs have been identified for CA-13. Alleles of 20 and 21 CAs are the most common and their population frequency was 0.68 and 0.24, respectively. The CA-22 marker contained a repetition of (GT)n(AG)n as was identified in the white European but not in the Canadian population. Alleles with 25 and 26 GT/AGs account for 18% and 75% of this group of samples, respectively. The expected rate of heterozygosity for either CA markers was 68%, although a value of 57% was observed by haplotype analysis, indicating an association of the two repeat markers. Nevertheless, the study of 62 females showed that with the combined use of CA-13 and CA-22 with BclI, approximately 71% would be informative for these markers. This number may increase to 81% if XbaI polymorphism is added. We propose that a better genetic diagnosis procedure for Chinese individuals would be first to look for the inversion mutation, secondly for one of the intragenic markers, and then at the PCR-SSCP analysis.

Severe haemophilia A in a female resulting from two de novo factor VIII mutations

A 2-year-old girl is described with severe haemophilia A (factor VIII: C < 0.01 units/ml). Both of her parents were phenotypically normal. Cytogenetic analysis on the proband demonstrated an interstitial X chromosome deletion encompassing Xq26-q28. Molecular studies with several polymorphic markers close to and within the factor VIII gene showed that the proband had inherited only the paternal factor VIII gene, indicating that the X chromosome deletion had occurred de novo in the maternal germ line. Further study of the factor VIII gene inherited by the proband from her father showed the presence of a de novo gene inversion mutation (a type 1, distal pattern inversion). Neither parent showed any evidence of the factor VIII inversion in their somatic DNA. The severe haemophilia A documented in this girl is therefore the result of two de novo mutations affecting the factor VIII gene, a maternally derived X chromosome deletion and a paternal factor VIII inversion mutation.