Identification of mutations in the FVII and FXIII genes of Maltese patients with unexplained bleeding tendency

Abstract

Factor VII (FVII) is one of the constituent factors of the extrinsic pathway of the coagulation cascade. The main role of Factor VII is to initiate the process of coagulation in conjunction with tissue factor (TF/Factor III). Factor XIII (FXIII) is an enzyme of the blood coagulation system that is coded by two different subunits located on different chromosomes, and is responsible for cross-linking and stabilising fibrin. Deficiency of this factor (FXIII) affects clot stability. Factor XIII levels are not measured routinely, but FXIII deficiency may be considered in patients with an unexplained bleeding tendency. This study aimed at identifying possible candidate variants in the FVII and FXIII genes which are likely to be the causative factors of the respective factor deficiency. This was done by sequencing DNA samples from 16 individuals attending the coagulation clinic and 80 individuals obtained from the MAMI study with specific selection criteria (high INR value, low and high FXIII activity) through Next Generation Sequencing. The variants obtained were bioinformatically and statistically analysed through the use of software such as FASTQC and SPSS. Two unknown high impact DNA variants in the FXIII A subunit gene were detected in the five FXIII deficiency individuals tested. A novel Glut602X stop gained variant was found in two siblings, whilst another unknown variant, a c.2046-2A>G splice acceptor variant, was found in two identical twins and another individual. These variants were not found in FXIII control samples, and it may be likely that such deleterious variants are responsible for the severe FXIII deficiency phenotype. A highly significant and rare FVII variant, the FVII Malta I, was found in six samples having high INR values, suspected to have FVII deficiency. Another two more common variants rs6046 and rs6042 were also discovered in 37 and 38 individuals respectively. As the FVII deficiency phenotype varies from being asymptomatic to a mild deficiency, it is possible that the phenotype is the result of the interaction between several low impact variants. Rs6046 and rs6042 have reduced penetrance, with the phenotype depending on the precise allelic combination By presenting these candidate variants, this study sets the foundation for further in-depth studies to confirm and understand the exact molecular basis behind these deficiencies, with the ultimate aim to providing the best suited case specific treatment.