Severe haemophilia A in a female: a compound heterozygote with nonrandom X-inactivation

Genetic causes of haemophilia in women and girls

Women and girls reported as "haemophilic females" may have complex genetic causes for their haemophilia phenotype. In addition, women and girls may have excessive bleeding requiring treatment simply because they are heterozygous for haemophilia alleles. While severe and moderate haemophilia are rare in females, 16% of patients with mild haemophilia A and almost one-quarter of those with mild haemophilia B seen in U.S. haemophilia treatment centres are women and girls. A phenotypic female with a low level of factor VIII or factor IX may be classified into one of the following categories of causality: homozygosity (two identical haemophilia alleles), compound heterozygosity (two different haemophilia alleles), hemizygosity (one haemophilia allele and no normal allele), heterozygosity (one haemophilia allele and one normal allele), genetic causes other than haemophilia and non-genetic causes. Studies required for classification may include coagulation parameters, F8 or F9 sequencing, F8 inversion testing, multiplex ligation-dependent probe amplification, karyotyping and X chromosome inactivation studies performed on the patient and parents. Women and girls who are homozygous, compound heterozygous or hemizygous clearly have haemophilia, as they do not have a normal allele. Heterozygous women and girls with factor levels below the haemostatic range also meet the definitions used for haemophilia treatment.

Inherited Bleeding Disorders in North Indian Children: 14 years' Experience from a Tertiary Care Center

Inherited bleeding disorders are not uncommon in pediatric practice: most of them being chronic, require lifelong replacement therapy. To frame a management policy, it is essential to assess the load and pattern of bleeding disorders in the local population. However, there is paucity of data reporting the clinical spectrum of coagulation and platelet function disorders in Indian children. Hence to find out the exact burden and clinico-investigational profile of these patients we conducted this study. In this retrospective case review, detailed clinical information was extracted from case records in 426 children with a suspected diagnosis of hereditary bleeding disorder registered in the Pediatric Hematology clinic of a tertiary referral centre over a period of 14 years (1998-2011) and pooled for analysis. In our cohort prevalence of hemophilia A, hemophilia B, platelet function disorders, von Willebrand disease and other rare factor deficiencies were 72%, 11%, 7%, 4% and 4% respectively. Common clinical spectrum included skin bleeds, arthropathy, mucosal bleeds. 10% had deeper tissue bleeding and 16% received replacement therapy at the first visit. Nearly 3/4th of cases were lost for follow up after the initial visit. Hemophilia A was the commonest inherited bleeding disorder in our population. Skin bleeds and arthropathy were common clinical presentations. Factor replacement therapy was restricted to a minority. There is an urgent need for establishing centres of excellence with administrative commitment for factor replacement therapy for comprehensive management of such children in resource-limited countries.

Investigation of inflicted injury in a young girl reveals mild haemophilia A and Turner's syndrome

A 2-year-old girl presented to casualty with a right knee effusion after apparently minor trauma. Inflicted injury was suspected and full forensic coagulation studies were performed which revealed a mild deficiency of factor VIII. Screening of the exons and intron/exon boundaries of F8 gene indicated that the child appeared to be homozygous for the missense mutation c.5123G>A (p.Arg1708His) in exon 14 of the F8 gene. This mutation has been reported to be associated with mild haemophilia A. The possibility of hemizygosity had been masked by the test kit employed but referral to the genetics service and subsequent array CGH resulted in a diagnosis of Turner syndrome.

Molecular mechanisms underlying hemophilia A phenotype in seven females

BACKGROUND

Hemophilia A (HA) in females is a rare observation. Here we describe various genetic mechanisms that result in phenotypic expression of HA in seven females.

METHODS

The F8 gene was examined in all patients and relatives by direct sequencing. Multiplex ligation-dependent probe amplification (MLPA) was performed for large deletion screening. X chromosome inactivation was studied by PCR analysis of a polymorphic CAG repeat in the first exon of the human androgen receptor (HUMARA) gene.

RESULTS

In two females sequencing of the F8 gene revealed homozygous missense mutations (Arg593Cys and Tyr1680Phe) as a consequence of consanguineous marriage. The third case was due to compound heterozygosity comprising the missense mutation Leu412Phe inherited from the carrier mother, together with a de novo large deletion spanning exon 9-22, probably originating from the germ cells of the healthy father. Three further cases shared a common mechanism representing heterozygous mutations in the F8 gene (Arg1781His, Arg327His, small deletion in exon 10) combined with non-random inactivation of the X chromosome. The final case describes a coincidental inheritance of HA and Coffin-Lowry syndrome in the same family. The HA phenotype results from a heterozygous small deletion affecting the F8 gene (c.6872 del CT leading to Thr2272fs) and a complete inactivation of the maternal X chromosome, which segregates with Coffin-Lowry syndrome in the two brothers of the proposita.

CONCLUSIONS

In conclusion, molecular genetic analysis represents an essentially valuable tool in elucidating the nature of the molecular mechanisms underlying the HA phenotype in females.

Female monozygotic twins discordant for hemophilia A due to nonrandom X-chromosome inactivation

We describe monozygotic female twins discordant for hemophilia A, born to a carrier mother and normal father. Affected twin A presented at age 1 year with excessive bruising and factor VIII procoagulant activity (FVIII:C) of less than 1% of normal. Twin B is an asymptomatic carrier with FVIII:C level of 42%. Peripheral blood DNA was tested for X-chromosome inactivation (methylation) patterns of the X-linked human androgen receptor gene, comparing the twins' patterns to parental. Twin A showed nonrandom inactivation skewed toward the paternal X, whereas twin B showed random X-inactivation. This is the first reported case of discordance for hemophilia A between female monozygotic twins.

Severe haemophilia A in a female resulting from an inherited gross deletion and a de novo codon deletion in the F8 gene

Haemophillia A (HA) is an X-linked bleeding disorder caused by mutations in the F8 gene. While the disease affects 1 in 5000 males, phenotypic expression of haemophilia A is rare in females, similar to other X-linked recessive disorders. We describe a 5-year-old female with severe haemophilia A. We determined the underlying molecular defect in the F8 genes of the proband and her closest family members by direct DNA sequencing, marker analysis and quantitative real-time polymerase chain reaction. The patient showed two different mutations in the F8 gene: the paternal copy of the F8 gene had a de novo p.Phe652/653 deletion in exon 13 while the maternally inherited gene showed a large deletion encompassing exons 1 to 22. The structural analysis of residues Phe652/Phe653 based on a three-dimensional model of activated factor VIII provides evidence of the impact of the mutant factor VIII protein in the clinical manifestations of the patient. This unusual finding highlights the need to perform a thorough molecular analysis including sequencing, marker and quantitative analyses to identify compound heterozygous females with HA.

Mutation spectrum of 122 hemophilia A families from Taiwanese population by LD-PCR, DHPLC, multiplex PCR and evaluating the clinical application of HRM

Background

Hemophilia A represents the most common and severe inherited hemorrhagic disorder. It is caused by mutations in the F8 gene, which leads to a deficiency or dysfunctional factor VIII protein, an essential cofactor in the factor X activation complex.

Methods

We used long-distance polymerase chain reaction and denaturing high performance liquid chromatography for mutation scanning of the F8 gene. We designed the competitive multiplex PCR to identify the carrier with exonal deletions. In order to facilitate throughput and minimize the cost of mutation scanning, we also evaluated a new mutation scanning technique, high resolution melting analysis (HRM), as an alternative screening method.

Results

We presented the results of detailed screening of 122 Taiwanese families with hemophilia A and reported twenty-nine novel mutations. There was one family identified with whole exons deletion, and the carriers were successfully recognized by multiplex PCR. By HRM, the different melting curve patterns were easily identified in 25 out of 28 cases (89%) and 15 out of 15 (100%) carriers. The sensitivity was 93 % (40/43). The overall mutation detection rate of hemophilia A was 100% in this study.

Conclusion

We proposed a diagnostic strategy for hemophilia A genetic diagnosis. We consider HRM as a powerful screening tool that would provide us with a more cost-effective protocol for hemophilia A mutation identification.

Haemophilia A: molecular insights

Haemophilia A is the most common inherited bleeding disorder caused by defects in the

Clin Chem Lab Med 2007;45:450–61.

Familial nonrandom inactivation linked to the X inactivation centre in heterozygotes manifesting haemophilia A

A basic tenet of the Lyon hypothesis is that X inactivation occurs randomly with respect to parental origin of the X chromosome. Yet, nonrandom patterns of X inactivation are common - often ascertained in women who manifest recessive X-linked disorders despite being heterozygous for the mutation. Usually, the cause of skewing is cell selection disfavouring one of the cell lineages created by random X inactivation. We have identified a three generation kindred, with three females who have haemophilia A because of extreme skewing of X inactivation. Although they have both normal and mutant factor VIII (FVIII) alleles, only the mutant one is transcribed; and, they share an XIST allele that is never transcribed. The skewing in this case seems to result from an abnormality in the initial choice process, which prevents the chromosome bearing the mutant FVIII allele from being an inactive X.

Skewed X-chromosome inactivation in monochorionic diamniotic twin sisters results in severe and mild hemophilia A

This study describes the genetic mechanisms responsible for the de novo occurrence of severe and mild hemophilia A in monozygotic twin females. Both twins were found to carry a previously known factor VIII mutation (Tyr16Cys) in the heterozygous state which most probably arose in the paternal germ line. Both twins showed concordant skewing of X inactivation toward the maternally derived normal X chromosome, the most severely affected twin exhibiting a higher percentage of inactivation of the normal X chromosome. The degree of skewing of X inactivation closely correlated with both the coagulation parameters and the clinical phenotype of the twins. Since these twins were monochorionic, such results suggest that the twinning event in this case has occurred after the onset of the X-inactivation period.

Factor VIII gene inversions and polymorphisms in Brazilian patients with haemophilia A: carrier detection and prenatal diagnosis

In families afflicted with haemophilia A, genetic counselling is often requested. Inversion mutations and polymorphic sites of the FVIII gene have been examined in a Brazilian population, with the aim of developing a strategy that would be accurate and informative for carrier analysis and prenatal diagnosis in Brazil. Patients with haemophilia A and families were studied. Inversion mutations in the FVIII gene were detected in 39.4% of severely affected patients, 85% of them being of distal type. No inversions were observed in patients with mild or moderate forms of the disease. Two bi-allelic polymorphisms were studied. Intron 18 SSCP and intron 19 RFLP analyses indicated the presence of a restriction site in 39.5% and 42.9% of haemophilics, respectively. Two multiallelic microsatellite polymorphisms in introns 13 and 22 were also studied; eight different alleles were detected in each system with a heterozygosity rate of 83.08% and 78.77%, respectively. When all four intragenic loci were examined in linkage analysis, the cumulative reliability was 100%. In conclusion, inversion mutation analysis should be the first-line test for Brazilian patients with severe haemophilia A. In cases of severe haemophilia A where no inversion could be detected or in mild or moderate haemophilia A, the use of all four polymorphisms is very informative for linkage analysis and should be used for carrier detection and genetic counselling in the Brazilian population.