Molecular diagnosis of inversions resulting from intron 22 rearrangement of F8 gene in a patients with hemophilia A and their families and genotype-phenotype association analysis
Authors: Bahrulolum Howra , Hashemi Mehrdad 
Published: July 2022

Background: Hemophilia A is an X-linked recessive bleeding disorder characterized by a qualitative and quantitative deficiency of coagulation factor VIII resulting from heterogeneous mutations in the factor VIII gene. About half of severe hemophilia A cases (40-50%) are caused by the F8 intron 22 inversion mutation. The development of inhibitor antibodies against transfused FVIII in patients with hemophilia A is the most significant treatment complication seen in hemophiliacs patients. Variations in the F8 gene, especially intron 22 inversions, are one of the genetic factors that lead to the development of FVIII inhibitors. The present study aimed to screen Intron 22 inversion type I and type II in severe hemophilia A patients and investigated its role as a predisposing factor for the inhibitor development. Furthermore, another aim of this study was to investigate a hypothesized association between the ABO blood group and the risk of inhibitor development in hemophilia A patients (including moderate and mild forms). Methods: Genetic analysis was conducted in 20 patients who were clinically diagnosed with severe hemophilia A and seven related female members by inversion-shifting PCR.Results: Intron 22 inversion mutation was detected in 35% (7/20) of patients with severe hemophilia A. Among them, 28% (2/7) had an inversion type I, and 72% (5/7) had an inversion type II. The frequency of intron 22 inversion variation in this small cohort study was almost similar to those reported in other populations, but the frequency of inversion type II was significantly higher than the frequencies of other reporting populations. Carrier status analysis showed that two cases were not carried abnormal alleles, 5 cases were carried inversion 22 type II and 2 cases were carried inversion 22 type I. The prior family history was shown in 70% of all patients and 71.1% (5/7) of hemophilia A patients with Inv22 variation. Inhibitor prevalence in patients was 15% (n=3) and seen in the mild, moderate, and severe phenotypes. The results indicated that there was no correlation between prior family history, as well as FVIII inhibitor development and intron 22 inversion variation. Our results also showed that the risk of inhibitor development was free from any significant correlation to the ABO blood group.Conclusions: The IS-PCR is a simple, rapid, and cost-effective method that can be used for both diagnosis of Inv22 variation in hemophilia A patient and carrier screening. Both approaches are important to determine carrier status and move forward with family planning. The prevalence of Inv22 of FVIII in this study is nearly like that of other populations. Despite the fact that the intron 22 inversion variant was related with 35% of severe hemophilia A phenotypic cases, it was not a substantial risk factor for inhibitor development. Furthermore, there was no significant association between ABO blood group and inhibitor development in this in this cohort of hemophiliacs.