Molecular genetic diagnosis in the group of hemophilia A patients in Belarus: 12 new allelic variants in the <i>F8</i> gene

Abstract

Hemophilia A is the most common severe bleeding disorder caused by various genetic changes in the F8 gene, leading to coagulation factor VIII deficiency. Hemophilia A is characterized by high heterogeneity of genetic defects. The severity of hemophilia A varies depending on the type of genetic defects in the F8 gene. More than 3000 unique variants of the F8 gene are associated with the hemophilia A. Approximately 30% of genetic defects occur de novo. The aim of this study is to determine the spectrum of genetic defects in the F8 gene in children with hemophilia A in Belarus. The study was approved by the Independent Ethics Committee and the Scientific Council of the Belarusian Research Center for Pediatric Oncology, Hematology and Immunology (the Republic of Belarus). The study included 98 patients with hemophilia A, who had been treated or followed up at the Belarusian Research Center for Pediatric Oncology, Hematology and Immunology (the Republic of Belarus). Patients were categorized into 3 groups based on the severity of their disease: severe (n = 82), moderate (n = 3), and mild (n = 13). Twenty (20.4%) patients had a history of inhibitors to factor VIII. For our study, we used venous blood samples. Genomic DNA was isolated from leukocyte suspension (obtained from the whole blood samples) using phenol-chloroform extraction. All severe hemophilia A patients were prescreened for intron 22 and 1 inversions in the F8 gene using inverse and multiplex polymerase chain reaction assays, respectively. Sequencing of F8 coding regions was carried out by next generation sequencing. All clinically relevant variants were confirmed by Sanger sequencing. Genetic testing revealed that 99% of the patients with hemophilia A (n = 97) had pathogenic variants in the F8 gene. Intron 22 and intron 1 inversion mutations within the F8 gene were detected in 45.1% (n = 37) and 1.2% (n = 1) patients with severe hemophilia A, respectively. Two patients had an abnormal pattern of intron 1 inversion, not previously described in the literature. A total of 48 different variants in the F8 gene were detected in 57 patients using next generation sequencing. Eleven of the 48 genetic variants identified have not been previously reported.