Genotyping of intron 22 inversion of factor VIII gene for diagnosis of hemophilia A by inverse-shifting polymerase chain reaction and capillary electrophoresis

Factor VIII inhibitor development in Egyptian hemophilia patients: does intron 22 inversion mutation play a role?

Background

Hemophilia A (HA) is an X-linked recessive bleeding disorder characterized by qualitative and quantitative deficiency of factor VIII (FVIII). The development of inhibitor antibodies against FVIII is the most challenging complication of treatment. Mutations in the FVIII gene is one of the genetic factors that leads to development of FVIII inhibitors especially intron 22 inversion (Inv22).

Objectives

This study was carried out to assess the frequency of Inv22 of FVIII gene in Egyptian patients with hemophilia A and its role as a risk factor for developing inhibitors.

Patients and methods

Seventy-two patients with severe HA and 48 patients with moderate HA were enrolled in the current study. All patients were treated on demand with either plasma-derived factor VIII or recombinant factor VIII concentrates. Genotyping of FVIII Inv22 was performed by LD-PCR while the presence and magnitude of inhibitor activity in blood was determined by the Bethesda assay.

Results

Around 23% of all hemophilia cases had positive Inv22. Intron 22 inversion mutation was detected in 6 and 33% of patients with moderate and severe HA respectively. Twenty-one cases (18%) of all hemophilic patients developed inhibitors. Thirty-7% of patients with Inv22 had inhibitor in their blood, almost all, but one, had severe HA. The risk of an inhibitor development during replacement therapy was four folds higher among Inv22 positive cases as compared with mutation negative peers (OR 4.3, 95% CI 1.6–11.9, P = 0.003).

Conclusions

The prevalence of Inv22 of F VIII in Egyptian hemophiliacs is nearly like that of other population. This mutation was more frequently detected among severe hemophilic patients as compared with moderately affected peers. The presence of Inv22 mutation significantly predispose to FVIII inhibitor development.

Capillary electrophoresis based on nucleic acid analysis for diagnosing inherited diseases

Most hereditary diseases are incurable, but their deterioration could be delayed or stopped if diagnosed timely. It is thus imperative to explore the state-of-the-art and high-efficient diagnostic techniques for precise analysis of the symptoms or early diagnosis of pre-symptoms. Diagnostics based on clinical presentations, hard to distinguish different phenotypes of the same genotype, or different genotypes displaying similar phenotypes, are incapable of pre-warning the disease status. Molecular diagnosis is ahead of harmful phenotype exhibition. However, conventional gold-standard molecular classifications, such as karyotype analysis, Southern blotting (SB) and sequencing, suffer drawbacks like low automation, low throughput, prolonged duration, being labor intensive and high cost. Also, deficiency in flexibility and diversity is observed to accommodate the development of precise and individualized diagnostics. The aforementioned pitfalls make them unadaptable to the increasing clinical demand for detecting and interpreting numerous samples in a rapid, accurate, high-throughput and cost-effective manner. Nevertheless, capillary electrophoresis based on genetic information analysis, with advantages of automation, high speed, high throughput, high efficiency, high resolution, digitization, versatility, miniature and cost-efficiency, coupled with flexible-designed PCR strategies in sample preparation (PCR-CE), exhibit an excellent power in deciphering cryptic molecular information of superficial symptoms of genetic diseases, and can analyze in parallel a large number of samples in a single PCR-CE, thereby providing an alternative, accurate, customized and timely diagnostic tool for routine screening of clinical samples on a large scale. Thus, the present study focuses on CE-based nucleic acid analysis used for inherited disease diagnosis. Also, the limitations and challenges of this PCR-CE for diagnosing hereditary diseases are discussed.

Accurate, simple, and inexpensive assays to diagnose F8 gene inversion mutations in hemophilia A patients and carriers

The most frequent mutations resulting in hemophilia A are an intron 22 or intron 1 gene inversion, which together cause ∼50% of severe hemophilia A cases. We report a simple and accurate RNA-based assay to detect these mutations in patients and heterozygous carriers. The assays do not require specialized equipment or expensive reagents; therefore, they may provide useful and economic protocols that could be standardized for central laboratory testing. RNA is purified from a blood sample, and reverse transcription nested polymerase chain reaction (RT-NPCR) reactions amplify DNA fragments with the F8 sequence spanning the exon 22 to 23 splice site (intron 22 inversion test) or the exon 1 to 2 splice site (intron 1 inversion test). These sequences will be amplified only from F8 RNA without an intron 22 or intron 1 inversion mutation, respectively. Additional RT-NPCR reactions are then carried out to amplify the inverted sequences extending from F8 exon 19 to the first in-frame stop codon within intron 22 or a chimeric transcript containing F8 exon 1 and the VBP1 gene. These latter 2 products are produced only by individuals with an intron 22 or intron 1 inversion mutation, respectively. The intron 22 inversion mutations may be further classified (eg, as type 1 or type 2, reflecting the specific homologous recombination sites) by the standard DNA-based "inverse-shifting" PCR assay if desired. Efficient Bcl I and T4 DNA ligase enzymes that cleave and ligate DNA in minutes were used, which is a substantial improvement over previous protocols that required overnight incubations. These protocols can accurately detect F8 inversion mutations via same-day testing of patient samples.