Reevaluation of von Willebrand disease diagnosis in a Croatian paediatric cohort combining bleeding scores, phenotypic laboratory assays and next generation sequencing: a pilot study.

Introduction: This study reevaluated von Willebrand disease (vWD) diagnosis in a Croatian paediatric cohort by combining bleeding scores (BS), phenotypic laboratory testing, and next-generation sequencing (NGS).

Materials and methods: A total of 25 children (11 males and 14 females, median age 10 years, from 2 to 17) previously diagnosed with vWD were included. BS were calculated using an online bleeding assessment tool. Phenotypic laboratory analyses included platelet count, platelet function analyser closure times, prothrombin time, activated partial thromboplastin time, von Willebrand factor antigen (vWF:Ag), vWF gain-of-function mutant glycoprotein Ib binding activity (vWF:GPIbM), vWF collagen binding activity (vWF:CBA), factor VIII activity (FVIII:C) and multimeric analysis. Next-generation sequencing covered regions of both vWF and FVIII genes and was performed on MiSeq (Illumina, San Diego, USA).

Results: Disease-associated variants identified in 15 patients comprised 11 distinct heterozygous vWF gene variants in 13 patients and one novel FVIII gene variant (p.Glu2085Lys) in two male siblings. Four vWF variants were novel (p.Gln499Pro, p.Asp1277Tyr, p.Asp1277His, p.Lys1491Glu). Three patients without distinctive variants had vWF:GPIbM between 30 and 50%. Patients with identified vWF gene variants had statistically significant lower values of vWF:GPIbM (P = 0.002), vWF:Ag (P = 0.007), vWF:CBA (P < 0.001) and FVIII:C (P = 0.002), compared to those without. Correlations between BS and phenotypic laboratory test results were not statistically significant for either of the tests.

Conclusion: The applied diagnostic approach confirmed the diagnosis of vWD in 13 patients and mild haemophilia A in two. Limited utility of BS in the paediatric population was evidenced.