Intron 22 inversion real-time polymerase chain reaction detection in haemophilia A families from central South Africa

Abstract

Haemophilia A is an X-linked recessive bleeding disorder characterised by deficiency of coagulation factor VIII (FVIII). [1] The disorder can be classified according to procoagulant levels of FVIII: patients with severe haemophilia A have levels of <1 IU/dL, those with moderate disease 1-5 IU/dL, and those with mild disease 5-40 IU/ dL. The disorder mainly affects males, at a rate of 1 in 5 000-10 000 worldwide. [1,2] The 2017 World Federation of Hemophilia survey [3] reported that 149 764 individuals were affected by haemophilia A globally, with only 1 848 reported in South Africa (SA). Haemophilia A is underdiagnosed in SA, as in many other developing countries, owing to a lack of access to diagnostic expertise. [4] There is currently only one genetic testing facility, which services all the haemophilia A treatment centres in SA. [4] Genetic research on haemophilia is therefore limited in SA, [4] as evident from the FVIII gene (F8) variant database, to which SA has made no contribution. [5] Genetic testing is of paramount importance in the comprehensive treatment plan for haemophilia A, since mutations in F8 are the cause of the disorder. Furthermore, F8 mutations may be associated with the development of FVIII inhibitors, [6] and variant detection allows for prenatal and carrier detection to enable genetic counselling of haemophilia A families. [7] According to the literature, 45% of all severe haemophilia A cases are associated with an inversion in intron 22 (inv22) of F8. [8,9] Based on gene expression, an mRNA conventional inv22 polymerase chain reaction (PCR) screening method was developed to allow rapid detection of inv22. [10] This method assumes the presence of an additional exon, called exon 23c, contained in the inv22 mutant FVIII transcript. [11] Exon 23c was found to be spliced to exon 22 of F8 in unrelated haemophilia A patients. [10] Objectives To detect the presence of inv22 in the haemophilia A population of central SA and potential haemophilia A carriers. This open-access article is distributed under Creative Commons licence CC-BY-NC 4.0.

Systematic Review of Genetic-Related Risk Factor and Inhibitor Epidemiology in People with Severe Hemophilia a from Africa: A 2023 Update

“…However, it is technically difficult to standardize and requires a high-quality DNA extract. This has probably motivated the development of alternative methods such as reverse PCR used in Egypt [36,37] or real-time PCR developed by Kloppers JF in South Africa in 2019 [38,39].…”

De Novo Intron 22 Inversion Carrier Detection—The Emerging Value of Genetic Analysis in a Developing Country

“…In that initial study we screened 62 people (27 families) with hemophilia A, including putative carriers, for the Inv22 variation. 5 Since the publication of our initial study's results and the implementation of Inv22 screening on our diagnostic platform, we have subsequently screened 28 more people with hemophilia (including carriers) from our local HTC. However, securing broader clinician buy-in in our country, especially with genetic carrier detection, with the clinical utility of genetic screening not always apparent in asymptomatic carriers, remains a problem.…”