Informativeness of linkage analysis for genetic diagnosis of haemophilia A in India

Association of Genetic Variant FVIII Gene and Factor VIII: A Pilot Study Among Hemophilia A Female Relatives in Saudi Arabia

Hemophilia A (HA) is an X-linked recessive disorder that results from mutations in the factor VIII gene (FVIII). Most affected patients are males due to the inheritance of mutations in the FVIII gene from their mothers. Females are mostly found to be carriers unless they inherited the mutation from both parents. Obligate carriers of HA are mothers whose sons are affected with HA, or daughters who inherit the mutation from their affected fathers. A possible carrier of HA could be any female who has one or more affected relatives with HA in her family. Hemophilia A carriers (HACs) could present with similar symptoms to affected patients, including low factor VIII level, and risk of bleeding especially after surgical procedures or postpartum hemorrhage.

OBJECTIVES

 Assessing the phenotype of possible HAC and its association with genetic variants in the FVIII gene for better screening methods for HAC.

METHODS

From the period between 25 June and 25 October 2021, the study was conducted at King Abdulaziz University Hospital in Jeddah, Saudi Arabia. We recruited seven mothers whose sons were affected with HA, and 18 possible HAC who are relatives to sever affected patients with HA. All 25 candidates were assessed for the FVIII level, activated partial thromboplastin time (APTT), and bleeding risk and sequenced a part of Exon14 in their FVIII gene.

RESULTS

Twenty-five percent of the participants show a low level of FVIII, however, none of them have prolonged bleeding nor suffer from bleeding tendency. We also identified two missense variants in six of the candidates, but the clinical significance of these variants has not been determined previously.

CONCLUSION

This pilot study is the first to explore the phenotype of several HAC in Saudi Arabia. A larger scale study with more HA patients and their female relatives is needed to understand the correlation between phenotype and genotype for better screening for HAC.

Determining common variants in patients with haemophilia A in South Vietnam and screening female carriers in their family members

AIMS

The aim of this study was to determine common variants in F8, including intron 22 inversion (Inv22), intron 1 inversion (Inv1) and point mutations, the transmission of these variants between patients with haemophilia A (HA) and their family members.

METHODS

Genetic analysis was conducted in 71 patients who were clinically diagnosed with HA and 152 related female members in South Vietnam by a combination of inversion PCR (I-PCR), multiplex PCR and direct sequencing.

RESULTS

Variants in F8, including Inv22, point mutations (with 37 genotypes) and two novel variants, occupied 60 patients with HA. Among severe patients, the rate of Inv22 was 44%. Missense was the common point mutation of over 50% in patients with moderate HA and mild HA. Inv1 was absent in all patients. F8 variants were also found in 119 female carriers (FCs) (78.3%) from families related to patients with HA. There were 56 mothers (93.3%) carrying F8 variants and passing the same variants to their sons.

CONCLUSIONS

These findings were the first to provide important information about the presence of Inv22 and point mutation in Vietnamese patients with HA, the mothers and their female family members. It demonstrated that genetic diagnosis and counselling for HA carriers were essential factors for future improvements in comprehensive and equitable healthcare polices for patients with HA and FCs in Vietnam.

Application of Indirect Linkage Analysis for Carrier Detection of Hemophilia A in Kurdistan Region of Iraq: Usefulness of Intron 18 BclI T>A, Intron 19 HindIII C>T, and IVS7 nt27 G>A Markers

Hemophilia A (HA) is the most common congenital X-linked coagulopathy caused by mutations in the factor VIII gene. One in 5000 to 10 000 male persons worldwide suffer from HA. It is the archetype of high-cost, low-volume disease. Therefore, identification of carriers is crucial to avoid the birth of affected males. Tracking of the defective X chromosome through indirect linkage analysis represents the most practical method for screening for carriers in developing countries. In this study, 227 individuals from 41 families with HA and 100 normal participants were recruited from the Kurdistan region of Iraq and evaluated for intron 18 BclI, intron 19 HindIII, and IVS7 nt 27 markers by polymerase chain reaction restriction fragment length polymorphism and direct sequencing. Among the studied women, 49%, 42%, and 14% were discovered to be heterozygous for BclI, HindIII, and IVS7 markers, respectively. Using BclI, HindIII, and IVS7 markers, 56%, 46%, and 17% of the families were informative, respectively. The combined informativity of these polymorphic sites reaches 66%. The current study illustrates the effectiveness of the BclI and HindIII markers for the diagnosis of HA carriers among the Iraqi Kurdish population.

Genetic analysis of bleeding disorders

Molecular genetic analysis of inherited bleeding disorders has been practised for over 30 years. Technological changes have enabled advances, from analyses using extragenic linked markers to next-generation DNA sequencing and microarray analysis. Two approaches for genetic analysis are described, each suiting their environment. The Christian Medical Centre in Vellore, India, uses conformation-sensitive gel electrophoresis mutation screening of multiplexed PCR products to identify candidate mutations, followed by Sanger sequencing confirmation of variants identified. Specific analyses for F8 intron 1 and 22 inversions are also undertaken. The MyLifeOurFuture US project between the American Thrombosis and Hemostasis Network, the National Hemophilia Foundation, Bloodworks Northwest and Biogen uses molecular inversion probes (MIP) to capture target exons, splice sites plus 5' and 3' sequences and to detect F8 intron 1 and 22 inversions. This allows screening for all F8 and F9 variants in one sequencing run of multiple samples (196 or 392). Sequence variants identified are subsequently confirmed by a diagnostic laboratory. After having identified variants in genes of interest through these processes, a systematic procedure determining their likely pathogenicity should be applied. Several scientific societies have prepared guidelines. Systematic analysis of the available evidence facilitates reproducible scoring of likely pathogenicity. Documentation of frequency in population databases of variant prevalence and in locus-specific mutation databases can provide initial information on likely pathogenicity. Whereas null mutations are often pathogenic, missense and splice site variants often require in silico analyses to predict likely pathogenicity and using an accepted suite of tools can help standardize their documentation.

Identification of mutations in the F8 and F9 gene in families with haemophilia using targeted high-throughput sequencing

INTRODUCTION

At present, many methods are available for the genetic diagnosis of haemophilia, including indirect linkage analysis, direct sequencing. However, these methods are time-consuming, labourious, and limited in their application. Therefore, the development of new, more effective techniques is necessary.

AIM

To detect the F8 and F9 gene mutations in patients with haemophilia and their female relatives in 29 haemophilia A (HA) and 11 haemophilia B (HB) families.

METHODS

FVIII

C and FIX:C were analyzed using one-stage method, and factor VIII and factor IX inhibitors were tested using the Bethesda method. Intron 22 and one inversions were identified using long-distance polymerase chain reaction (PCR) and standard PCR. Non-inversion mutations of the F8 and F9 gene were identified by targeted high-throughput sequencing. All mutations were verified by Sanger sequencing.

RESULTS

Intron 22 inversion was detected in eight HA families and intron one inversion was detected in one HA family. Apart from the inversion mutations, 20 mutations were identified in HA families, including 17 previously reported and three novel mutations: c.5724G>A (p.Trp1908*), c.6116-1_6120delGAGTGTinsTCC (p.Lys2039Ilefs*13), and c.5220-2A>C. We found a complex rearrangement in HA: intron one inversion concomitant with exon one deletion. In HB, eight recurrent mutations were detected, including six missense mutations and two nonsense mutations.

CONCLUSION

Targeted high-throughput sequencing is an effective technique to detect the F8 and F9 gene mutations, especially for the discovery of novel mutations. The method is highly accurate, time-saving and shows great advantage in uncovering large deletion mutations and also in distinguishing the wild-type genotype and heterozygous large deletions.

Prevalence of IVS10nt-18G/A in Calabrian patients with moderate/mild hemophilia A and relation with Factor VIII inhibitor antibodies

Hemophilia A is an X-linked bleeding disorder caused by widespread mutations in the factor VIII gene. In the course of a screening to research some hemophilia A mutations, our team has identified and posted a previously unreported nucleotide change in intron 10 in 20 patients with hemophilia A. We tried to identify a possible blood relationship between the people with this mutation, performing a backwards study of every family tree. First, we interviewed the patients and, if possible, parents and grandparents. When direct memory was no longer available, we consulted Registries of Births, Marriages and Deaths, and if these data were not sufficient, going backwards in time, we consulted registries of parish churches where newborns were baptized. The studied mutation was present in 33 hemophilic patients living in Calabria, 28 of them related. Three patients, carriers of this mutation, developed an FVIII inhibitor. In all the cases, the inhibitor development followed intensive treatments, after many days of exposure. Our study displayed the presence of a responsible moderate hemophilia A mutation, limited apparently to our country, probably because of a single ancestral event, and connected with FVIII inhibitor development.

Screening of intron 1 inversion and three intragenic factor VIII gene polymorphisms in Pakistani hemophilia A families

Indirect linkage analysis using highly informative polymorphic markers is the method of choice for carrier detection of hemophilia A in developing countries because direct DNA or mRNA sequence analysis is manifold costly and difficult than indirect gene tracking. Worldwide populations have revealed marked variation in the informativeness of polymorphic markers because of which each country has to select its own panel of markers for linkage analysis in hemophilia A families. The present study aimed at determining the informativeness of three factor VIII gene polymorphisms [intron 13(CA)n repeats, HindIII and AlwNI] in the Pakistani population. One hundred and forty-three individuals from 32 hemophilia A families and 68 unrelated anonymous females from the general population were screened for these polymorphisms using PCR and RFLP techniques. An inversion in intron 1 of the factor VIII gene causing 2-5% of severe hemophilia A cases was also screened in 128 Pakistani hemophilia A patients. None of the affected individuals carried the intron 1 inversion at least in peripheral blood leucocytes. The informativeness of intron 13 repeats, HindIII and AlwNI was 59.1% (13/22 hemophilia A families revealing five different alleles), 40.6% (13/32 hemophilia A families) and 6.25% (2/32 hemophilia A families), respectively. The cumulative informativeness of intron 13 repeats and HindIII was 63.6% (14/22 hemophilia A families), revealing strong linkage disequilibrium between these two polymorphic markers. These results suggest that there is a need to determine the informativeness of other polymorphic markers of the factor VIII gene to achieve 100% success rate for carrier detection of hemophilia A in Pakistan.

Prenatal diagnosis and preimplantation genetic diagnosis: novel technologies and state of the art of PGD in different regions of the world

Prenatal diagnosis (PND) aims to provide accurate, rapid results as early in pregnancy as possible. Conventional PND involves sampling cells of foetal origin by chorionic villus sampling at 11-14th weeks of pregnancy or amniocentesis after 15th week. These are invasive procedures and have a small but significant rate of 0.5% to 1% for loss of pregnancy. An alternative to existing methods for conventional PND for couples at risk of transmitting a genetic disease to their child is preimplantation genetic diagnosis (PGD). PGD is a newly emerging form of a very early prenatal diagnosis. The technique combines assisted reproductive technology with molecular genetics and cytogenetics to allow the identification of abnormality in embryos prior to implantation. The diagnosis of genetic disease in human preimplantation embryos was pioneered in the late 1980s for testing of aneuploidy, single gene and X-linked disease, such as cystic fibrosis, haemophilia and chromosomal abnormalities. The PGD-related legal and ethical issues have been debated at many levels both nationally and internationally. The attitude towards PGD varies substantially not only in different parts of the world but also within the Europe, owing to scientific, cultural and religious differences. PGD has become widely practised throughout the world for various indications and can substantially decrease the eventual risks of passing a genetic undesired condition of the offspring. Nevertheless, its extension to some new and non-medical indications has raised ethical concerns, in particular its potential eugenic dimension.

A set of five microsatellite markers linked to F8 gene can detect haemophilia A carriers across India

  Haemophilia A (HA) is an X-linked recessive bleeding disorder, primarily because of defects in the 186-kb long factor VIII gene (F8) affecting 1-2 men per 10,000 worldwide. Available markers for carrier detection are not effective in all populations, especially in India. In this study, we have chosen a set of five microsatellite markers, namely, DSX9897, DSX1073, intron 1 (GT)(n) , intron 22 (CA)(n) and intron 25 (CA)(n) , in and around the F8 gene to achieve better sensitivity for carrier detection. Each marker locus has been PCR amplified in the individual DNA samples using fluorescent markers followed by genotyping experiment in automated sequencer. Genotype calls have been made by GeneMapper Software (version 4). Allele frequency of each microsatellite marker was calculated manually. Heterozygosity was determined by counting the heterozygotes in the female subset. We have shown that in 253 normal individuals from 20 different ethnic groups of India, the heterozygosity for the markers ranged from 0.25 to 0.54; and for the entire subset of 102 female samples we could successfully discriminate between the two X-chromosomes using these five markers. These markers could also discriminate between the two X-chromosomes for each of 39 obligate carriers included in this study. In conclusion, this panel of five markers around the F8 locus can be used for carrier detection of HA with higher sensitivity across India for families affected with the disease.

Analysis of five polymorphic DNA markers for indirect genetic diagnosis of haemophilia A in the Brazilian population

Hemophilia A is an X-linked, inherited, bleeding disorder caused by the partial or total inactivity of the coagulation factor VIII (FVIII). Due to difficulties in the direct recognition of the disease-associated mutation in the F8 gene, indirect diagnosis using polymorphic markers located inside or close to the gene is used as an alternative for determining the segregation of the mutant gene within families and thus for detecting carrier individuals and/or assisting in prenatal diagnosis. This study characterizes the allelic and haplotype frequencies, genetic diversity, population differentiation and linkage disequilibrium of five microsatellites (F8Int1, F8Int13, F8Int22, F8Int25.3 and IKBKG) in samples of healthy individuals from São Paulo, Rio Grande do Sul and Pernambuco and of patients from São Paulo with haemophilia A to determine the degree of informativeness of these microsatellites for diagnostic purposes. The interpopulational diversity parameters highlight the differences among the analyzed population samples. Regional differences in allelic frequencies must be taken into account when conducting indirect diagnosis of haemophilia A. With the exception of IKBKG, all of the microsatellites presented high heterozygosity levels. Using the markers described, diagnosis was possible in 10 of 11 families. The F8Int22, F8Int1, F8Int13, F8Int25.3 and IKBKG microsatellites were informative in seven, six, five and two of the cases, respectively, demonstrating the effectiveness of using these microsatellites in prenatal diagnosis and in carrier identification in the Brazilian population.

Molecular pathology of haemophilia A in Indian patients: identification of 11 novel mutations

BACKGROUND

The identification of pathogenic mutations in haemophilia A (HA) patients is important as a basis for genetic diagnosis and also for the assessment of clinical manifestations.

METHOD

We analyzed 36 inversion negative congenital HA cases (28 unrelated and 8 familial) by multiplex PCR and the conformation sensitive gel electrophoresis (CSGE) technique, followed by DNA sequencing. The pathogenicity of each of these mutations was assessed using various prediction software.

RESULTS

We found 17 missense, 5 deletions, 3 insertions, and 2 nonsense mutations, out of which 16 were recurrent and 11 novel. All novel substitution mutations were found to be deleterious using the prediction softwares. We also encountered a double mutation (1 novel and 1 hot-spot mutation) in a family with a strong family history. A missense mutation in heterozygous state was also detected in a female bleeder with very low factor VIII levels, probably due to extreme lyonization.

CONCLUSION

High heterogeneity in mutational profile has been observed in the present study. The outcome of this study would enable us to give an accurate diagnosis in all affected families by direct mutation analysis.

Genotyping of intron 22-related rearrangements of F8 by inverse-shifting PCR in Egyptian hemophilia A patients

Hemophilia A (HA) is the most common severe bleeding disorder in humans, affecting one in 5,000 male births. In severe HA, intron 22 inversion of F8 is the most prevalent mutation, accounting for 40-50% of all mutations; however, little is known about the disease-causing mutations among Egyptian hemophiliacs. We aimed at genotyping all possible known DNA rearrangements of intron 22 of F8 in Egyptian HA patients. Peripheral blood samples were collected from 30 Egyptian HA patients (13 severe, ten moderate, and seven mild cases). Genotyping of F8 intron 22 rearrangements was performed by inverse-shifting PCR (IS-PCR). Our study revealed that seven patients (23.3%) had inversion 22, three patients (10%) had deletion 22, and 20 patients (66.7%) carried the wild-type allele. No intron 22 duplication was detected. The relative proportion of inversion 22-type 1 to inversion 22-type 2 was 85.7% and 14.3%, respectively, whereas the relative proportion of deletion 22-type 1 to deletion 22-type 2 was 33.3% and 66.7%, respectively. A statistically highly significant relation was found between disease severity and F8 intron 22 rearrangements (p = 0.008). Among severe cases, 46.1% had inversion 22, 23.1% had deletion 22, and 30.8% carried the wild-type allele. We conclude that F8 intron 22 inversion/deletion is responsible for about one third of disease-causing mutations among Egyptian hemophiliacs and for nearly 70% in severe cases. In addition, F8 intron 22 inversion/deletion by IS-PCR has proven to be a rapid and robust technique and might be the recommended tool for genetic analysis of HA patients specially with severe cases in developing countries.

Screening for hemophilia A carriers: utility of PCR-RFLP--based polymorphism analysis

Health schemes are promoting application of molecular diagnosis and screening in peripheral diagnostics labs. Intragenic restriction fragment length polymorphisms in the intron 18 (BclI), intron 19 (HindIII), and intron 22 (XbaI) of the Factor VIII gene were studied in 100 patients with hemophilia A and their relatives at risk from different regions of north India. For Bcl I, HindIII, and XbaI, the positive allele frequency was 0.57, 0.38, and 0.43, respectively, and heterozygosity was 0.54, 0.49, 0.41, respectively, whereas the heterozygosity in terms of informativity of the above markers was 53% for BclI, 44% for HindIII, and 34% for XbaI. Combined informativity of these markers was 77%. Review of Indian and world literature shows a marked variation in the informativity of polymorphic sites. Screening for carriers forms the baseline for prevention of hemophilia A. Polymerase chain reaction-restriction fragment length polymorphism is a low-cost procedure, efficient in the north Indian population.

Factor VIII gene haplotypes and linkage disequilibrium for the indirect genetic analysis of hemophilia A in India

Genomic consequences of factor VIII gene haplotypes for the indirect genetic analysis of haemophilia A has not been done in India hitherto. Consequently, BclI/intron18, HindIII/intron 19, and XbaI/intron 22 restriction sites were investigated in 159 individuals from 42 families with hemophilia A. The frequencies of haplotype II, IV, VI, that is, BclI (+)-HindIII (-)- XbaI (+), BclI (+)HindIII (+)-XbaI (-), and BclI (-)-HindIII (-)-XbaI (+) were 0.312, 0.198, and 0.164 respectively. The high heterogeneity of haplotype II highlighted its potential for indirect genetic diagnosis of factor VIII. Analysis revealed strong but incomplete linkage disequilibrium (D' = 0.76, 0.68, and 0.51) between BclI/HindIII, HindIII/XbaI, and BclI/XbaI, respectively. The overall cumulative polymorphism information content (PIC) of these three markers increased from 0.36 to 0.80. Escalation of PIC up to 80% in the present study suggests that haplotyping of factor VIII gene determines better prognosis in the direction of indirect genetic analysis of hemophilia A.

Second trimester antenatal diagnosis in rare coagulation factor deficiencies

Prenatal diagnosis is sought after for those genetic disorders, whose management is not satisfactory either because of the outcome or owing to extreme cost involved in the management of the patients affected by a specific disorder. Severe hemophilia and homozygous thalassemia are the 2 disorders for which there is an increasing demand for prenatal diagnosis in India. Rare severe deficiencies of coagulation factor X (FX) and factor VII (FVII) may present with severe bleeding manifestations. Because of their rarity the laboratory offering prenatal diagnosis for severe hemophilia and thalassemia may not be in a position to provide genetic diagnosis in the fetus. In this communication, we describe 2 families, 1 with an index patient of severe FVII deficiency and the other with severe FX deficiency where successful prenatal diagnosis was given after cordocentesis between 17 and 19 weeks using a battery of coagulation factor assays. Follow-up studies were performed 3 to 4 months after delivery and the diagnoses were reconfirmed on these babies by a repeat factor assay for FX and FVII deficiency, respectively.

Robustness of factor assays following cordocentesis in the prenatal diagnosis of haemophilia and other bleeding disorders

Prenatal diagnosis is the generally accepted option for genetic disorders including haemophilias and other bleeding disorders. Cord blood analysis between 17.4 and 20.6 weeks of gestation was performed in 172 confirmed carriers belonging to families of haemophilia A, haemophilia B, von Willebrand disease (VWD), factor VII and X deficiency; 133 were carriers for haemophilia A, 30 for haemophilia B, six for type 3 VWD, two for FX deficiency and one for FVII deficiency. The approach to the cord was either transabdominal or transamniotic. The volume of blood collected varied between 1 and 2 mL. In case of haemophilias, the diagnosis was offered by factor VIII/IX:C activity and antigen assays wherever required. In case of VWD, the diagnosis was based on von Willebrand factor antigen assays as detected by ELISA along with FVIII:C assay while in cases of FVII and FX deficiency, the diagnosis was based on FVII:C and FX:C respectively. The factor levels were compared with the normal range established in the laboratory for different coagulation factors between 18 and 21 weeks of gestation in women tested for other haematological disorders. Only in two cases, the procedure had to be repeated for reasons of extensive maternal contamination. All the deliveries have been followed up and the diagnoses reconfirmed by repeat clotting factor assays and DNA analysis whenever informative. Simple precautions like collection of fetal blood samples in smaller volumes in separate tubes, assaying multiple coagulation factors in the fetal blood samples helped us to offer diagnoses in all the women analysed. No fetal death or abortion was reported following the procedure. We suggest that accurate fetal blood sampling is a safe technique for the diagnosis of many of the bleeding disorders in places where genetic diagnostic services are not available.

First-trimester prenatal diagnosis in haemophilia A and B families--10 years experience from a centre in India

During the last 10 years (1995-2005) we have offered diagnosis in 438 families out of 502 families referred, by chorionic villus sampling procedure between 10 and 12 weeks of pregnancy in severe haemophilia A and B families. Sixty four families could not be offered a diagnosis in the first trimester either due to non-informativeness with the available techniques or due to the absence of affected members in the family and were subsequently offered diagnosis in the second trimester by direct analysis of factor VIII/IX clotting activity and antigen in the fetal blood samples. For first-trimester diagnosis in the chorionic villus samples, we have used both direct and indirect methods, that is, intron 22 and 1 inversions in the factor VIII gene, a multiplex PCR for the detection of gross deletions in the factor IX gene and RFLP analysis using a battery of markers within and outside the factor VIII/IX gene. The informativeness of all these techniques was found to be 92.21% in case of haemophilia A and 83.91% in case of haemophilia B. We followed up 122 children out of 326 (diagnosed unaffected prenatally) after birth and the diagnosis was adequately reconfirmed by both factor assays and by DNA analysis. Only one case of misdiagnosis was detected so far (0.22%), where the diagnosis was based only on the extragenic marker of the factor VIII gene.

Identification of factor VIII gene mutations in 101 patients with haemophilia A: mutation analysis by inversion screening and multiplex PCR and CSGE and molecular modelling of 10 novel missense substitutions

Haemophilia A (HA) is an X-linked bleeding disorder caused by diverse mutations in the human coagulation factor VIII (FVIII) gene. We have analysed DNA from 109 unrelated Indian patients with HA for their FVIII gene defects. Among these patients 89 (82%) had severe (FVIII:C <1%) HA, 11 (10%) had moderate (FVIII:C 1-5%) HA and nine (8%) had mild (FVIII:C 5-30%) HA. These patients were first screened for the common intron 22 and intron 1 inversions. Inversion negative samples were screened for point mutations by a multiplex PCR and conformation sensitive gel electrophoresis strategy. Mutations were identified in 101 of the 109 patients. These included two (2%) intron 1 and 51 (51%) intron 22 inversions, four (4%) gross deletions and 44 (43%) point mutations. Twenty-nine novel causative mutations, including 11 missense, seven frameshift, five nonsense mutations, three splice site defects and three gross deletions were detected. Ten of the novel missense mutations were studied by molecular modelling. Two different (Thr2253Pro and Pro1392fs) mutations were seen in four unrelated families and FVIII gene haplotyping suggested a common founder effect. Seven of these 109 patients had inhibitors. Among them, four had intron 22 inversions, one had a novel gross deletion (delexon 2-9) and one a nonsense mutation (Trp1535Stop). In one of these patients, no mutation could be identified in the FVIII gene. A Thr2253Pro novel mutation and an intron 22 inversion were identified in two female haemophiliacs. The data from this study suggests that the spectrum of gene defects in Indian patients with HA is as heterogeneous as reported in other populations.

Genetic diagnosis of haemophilia and other inherited bleeding disorders

Inherited deficiencies of plasma proteins involved in blood coagulation generally lead to lifelong bleeding disorders, whose severity is inversely proportional to the degree of factor deficiency. Haemophilia A and B, inherited as X-linked recessive traits, are the most common hereditary hemorrhagic disorders caused by a deficiency or dysfunction of blood coagulation factor VIII (FVIII) and factor IX (FIX). Together with von Willebrand's disease, a defect of primary haemostasis, these X-linked disorders include 95% to 97% of all the inherited deficiencies of coagulation factors. The remaining defects, generally transmitted as autosomal recessive traits, are rare with prevalence of the presumably homozygous forms in the general population of 1:500,000 for FVII deficiency and 1 in 2 million for prothrombin (FII) and factor XIII (FXIII) deficiency. Molecular characterization, carrier detection and prenatal diagnosis remain the key steps for the prevention of the birth of children affected by coagulation disorders in developing countries, where patients with these deficiencies rarely live beyond childhood and where management is still largely inadequate. These characterizations are possible by direct or indirect genetic analysis of genes involved in these diseases, and the choice of the strategy depends on the effective available budget and facilities to achieve a large benefit. In countries with more advanced molecular facilities and higher budget resources, the most appropriate choice in general is a direct strategy for mutation detection. However, in countries with limited facilities and low budget resources, carrier detection and prenatal diagnosis are usually performed by linkage analysis with genetic markers. This article reviews the genetic diagnosis of haemophilia, genetics and inhibitor development, genetics of von Willebrand's disease and of rare bleeding disorders.

Use of Intron 1 and 22 inversions and linkage analysis in carrier detection of hemophilia A in Indians

BACKGROUND

Hemophilia A is an X-linked recessively inherited bleeding disorder characterized by deficiency of procoagulant factor VIII (FVIII).

METHODS

Sixty unrelated hemophilia A patients and their family members have undergone tests for carrier detection by linkage analysis using the polymorphic markers Bcl I, Xba I and Intron 13 or 22 VNTRs. In families of sporadic hemophiliacs, the carrier status of female subjects was ascertained by linkage analysis along with FVIII:C/VWD Ag estimation.

RESULTS

Of the 33 families with positive family history, the defective X chromosome was tracked in 28 mothers. The carrier status of females from hemophilia A families with positive family history, ascertained by linkage analysis and Intron 22 and 1 inversion, was made out in 85% cases. FVIII:C/VWF Ag ratio was evaluated in 36 females from 9 sporadic hemophilic families. Using the FVIII:C/VWF Ag ratio along with linkage analysis, carrier status was determined in 9 (25%) of the 36 females studied. Using Intron 22 inversion along with linkage analysis and FVIII:C/VWF Ag estimation, the informativity in female subjects from families of sporadic hemophiliacs increased from 25% to 52%.

CONCLUSION

In the West, linkage analysis with Bcl I, Xba I and Intron 13 or 22 VNTR markers and inversion 22 offers a good tool for carrier detection of hemophilia A in India.

A highly informative, multiplexed assay for the indirect detection of hemophilia A using five-linked microsatellites

BACKGROUND

Hemophilia A is a severe bleeding disorder caused by almost 1000 different known mutations in the F8C gene. Direct mutation analysis is sometimes difficult for this disorder. When a mutation cannot be found, linkage analysis can be used for prenatal and carrier diagnosis.

AIM

To develop a rapid and effective system for carrier detection and prenatal diagnosis of hemophilia A based on a single-multiplexed polymerase chain reaction (PCR) reaction utilizing five microsatellite markers.

PATIENTS AND METHODS

Two intronic microsatellites and three other markers flanking the factor VIII gene were ascertained, and primers were designed for multiplex PCR amplification. A kindred with Hemophilia A was tested for linkage using the panel of primers, and informativity in the general population was ascertained by testing 50 unrelated females.

RESULTS

Co-amplification of all microsatellites was optimized using DNA extracted by standard methods. Rapid detection and sizing of products were carried out using an automated DNA sequencer. The combined microsatellite panel was informative in each of the kindreds tested, and in 100% of the 50 unrelated females (95% CI 94.2-100%).

CONCLUSIONS

This method enables the indirect detection of hemophilia A for patients in whom mutations cannot be found, facilitating carrier testing and prenatal analysis. It is rapid and straightforward compared with many other published protocols, and offers a high degree of informativity.

A rapid multifluorescent polymerase chain reaction for genetic counselling in Chinese haemophilia A families

Linkage analysis is a widely used strategy for genetic counselling in haemophilia A (HA) families. We attempted to develop more informative markers closely linked to factor VIII (FVIII) gene and establish a rapid multifluorescent polymerase chain reaction (PCR) method with these markers. Five extragenic (DXS15, DXS9901, G6PD, DXS1073 and DXS1108) and one intragenic (F8Civs13) markers were examined in 118 healthy individuals and 12 HA families which had been diagnosed before. Five extragenic markers were within an interval of about 1.5 Mb to FVIII gene and located on each side of the gene. The expected heterozygote rate (HR) of DXS15, DXS9901, G6PD, DXS1073, DXS1108 and F8Civs13 were 74.97%, 79.77%, 56.06%, 59.92%, 39.97% and 47.61%, while the observed HR were 88.24%, 82.35%, 21.57%, 62.75%, 35.29% and 52.94%. When six polymorphic markers were combined together, all the studied females were informative in at least one of these markers and 29.41% of them were detected informative in three markers with the highest frequency. The diagnostic rates of DXS15, DXS9901, G6PD, DXS1073, DXS1108 and F8Civs13 in 12 haemophilia families were 75.00%, 91.67%, 41.67%, 75.00%, 33.33% and 66.67% respectively. All the genetic diagnosis was consistent with the result we analysed before and no recombination was observed. Family 1 was given as an example in this study and was found to be informative in three polymorphic markers DXS15, DXS9901 and DXS1073. The patient's sister was detected the same allele as the proband, but her male fetus did not inherit the affected allele from her, which was consistent with the result of sequencing. It was demonstrated that the multifluorescent PCR method established in this study was convenient and efficient and can be applied to carrier detection and prenatal diagnosis in HA families.