Next generation sequencing in bleeding disorders: two novel variants in the F5 gene (Valencia-1 and Valencia-2) associated with mild factor V deficiency.

Inherited bleeding coagulation disorders (IBCDs) have a powerful diagnostic tool in next generation sequencing (NGS) that not only offers confirmation of diagnosis but also aids in genetic counselling, prenatal diagnosis and helps to predict the clinical course and follow-up of a disease. In our group, targeted-NGS using a Custom SureSelect QXT Panel (Agilent Technologies, Inc., Santa Clara, CA, USA) was designed to screen for causal variants in 40 genes related with the coagulation cascade. In this work, we used NGS for screening all the coding and intronic boundary regions of F5 gene in two patients affected by factor V (FV) deficiency (parahemophilia). Two new mutations were found: c.4745A>G (p.Tyr1582Cys, NM_000130.4) and c.1999_2002dupAATT (p.Ser668ter; NM_000130.4), both located in exon 13 of the F5 gene. We designated them Valencia-1 and Valencia-2 respectively. Valencia-1 could provoke loss of the fifth cupredoxin domain of the FV, and would be responsible for its defective activity. Valencia-2 prematurely stops the translation of mRNA, resulting in a truncated FV protein which lacks completely the B domain and the light chain. NGS has permitted to describe an increasing number of FV deficiency-causing mutations and a better understanding of FV's structure and function. The description of deficiency-causing mutations will continue to increase our knowledge of the functional residues of FV, as well as those which are involved in the correct folding of the protein. In this sense, NGS is a useful tool for studying IBCDs, as permits studying the whole coagulation cascade at once and gives a global view of the patient's genetic background.