Molecular characterization of female hemophilia A by multiplex ligation-dependent probe amplification analysis and X-chromosome inactivation study

FVIII at the crossroad of coagulation, bone and immune biology: Emerging evidence of biological activities beyond hemostasis

Hemophilia A is an X-linked hereditary disorder that results from deficient coagulation factor VIII (FVIII) activity, leading to spontaneous bleeding episodes, particularly in joints and muscles. FVIII deficiency has been associated with altered bone remodeling, dysregulated macrophage polarization, and inflammatory processes that are associated with the neoformation of abnormal blood vessels. Treatment based on FVIII replacement can lead to the development of inhibitors that render FVIII concentrate infusion ineffective. In this context, hemophilia has entered a new therapeutic era with the development of new drugs, such as emicizumab, that seek to restore the hemostatic balance by bypassing pathologically acquired antibodies. We discuss the potential extrahemostatic functions of FVIII that may be crucial for defining future therapies in hemophilia.

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.

An intronic mutation c.6430-3C>G in the F8 gene causes splicing efficiency and premature termination in hemophilia A

: Hemophilia A is a bleeding disorder caused by coagulation factor VIII protein deficiency or dysfunction, which is classified into severe, moderate, and mild according to factor clotting activity. An overwhelming majority of missense and nonsense mutations occur in exons of F8 gene, whereas mutations in introns can also be pathogenic. This study aimed to investigate the effect of an intronic mutation, c.6430-3C>G (IVS22-3C>G), on pre-mRNA splicing of the F8 gene. We applied DNA and cDNA sequencing in a Chinese boy with hemophilia A to search if any pathogenic mutation in the F8 gene. Functional analysis was performed to investigate the effect of an intronic mutation at the transcriptional level. Human Splicing Finder and PyMol were also used to predict its effect. We found the mutation c.6430-3C>G (IVS22-3C>G) in the F8 gene in the affected boy, with his mother being a carrier. cDNA from the mother and pSPL3 splicing assay showed that the mutation IVS22-3C>G results in a two-nucleotide AG inclusion at the 3' end of intron 22 and leads to a truncated coagulation factor VIII protein, with partial loss of the C1 domain and complete loss of the C2 domain. The in-silico tool predicted that the mutation induces altered pre-mRNA splicing by using a cryptic acceptor site in intron 22. The IVS22-3C>G mutation was confirmed to affect pre-mRNA splicing and produce a truncated protein, which reduces the stability of binding between the F8 protein and von Willebrand factor carrier protein due to the loss of an interaction domain.

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.

Heterogeneous lengths of copy number mutations in human coagulopathy revealed by genome-wide high-density SNP array

BACKGROUND

The recent advent of genome-wide molecular platforms has facilitated our understanding of the human genome and disease, particularly copy number aberrations. We performed genome-wide single nucleotide polymorphism-array in hereditary coagulopathy to delineate the extent of copy number mutations and to assess its diagnostic utility.

DESIGN AND METHODS

The study subjects were 17 patients with hereditary coagulopathy from copy number mutations in coagulation genes detected by multiple ligation-dependent probe amplification. Eleven had hemophilia (7 hemophilia A and 4 hemophilia B) and 6 had thrombophilia (4 protein S deficiency and 2 antithrombin deficiency). Single nucleotide polymorphism-array experiments were performed using Affymetrix Genome-Wide Human SNP arrays 6.0.

RESULTS

Copy number mutations were identified by single nucleotide polymorphism-array in 9 patients, which ranged in length from 51 Kb to 6,288 Kb harboring 2 to ~160 genes. Single nucleotide polymorphism-array showed a neutral copy number status in 8 patients including 7 with either a single-exon copy number mutation or duplication mutations of PROS1.

CONCLUSIONS

This study revealed unexpectedly heterogeneous lengths of copy number mutations underlying human coagulopathy. Single nucleotide polymorphism-array had limitations in detecting copy number mutations involving a single exon or those of a gene with homologous sequences such as a pseudogene.