Targeted DNA Sequencing for Hemophilia A, B, and von Willebrand Disease: Analytical Precision in Clinical Laboratories and Improved Disease Characterization

Hemophilia A, B, and von Willebrand disease correspond to more than 90% of all inherited bleeding disorders associated with coagulation factor deficiencies. Symptoms between these deficiencies may vary greatly and yet are often phenotypically similar. Bleeding episodes can range from mild to severe, at times with life threatening hemorrhages. Currently, biochemical assays are performed to assess the function of each coagulation factor, but diagnosis remains cumbersome and prone to multiple sources of variability between laboratories. Genetic evaluation allows for the examination of multiple coagulation factor genes simultaneously and may quickly identify possible causes to the disease. Additionally, genetic testing should be more reproducible and readily comparable between clinical laboratories. In this work we evaluate the potential use of targeted sequencing of three coagulation factors genes – F8, F9 and VWF – for the concurrent diagnosis and characterization of hemophilia A, B, and von Willebrand disease samples. For targeted DNA sequencing we selected specific DNA probes using genomic coordinates spanning the complete intronic and exonic regions of the three genes, as well as flanking gene sequences. Eleven hemophilia A samples and four hemophilia B samples, clinically characterized and submitted to Sanger sequencing for F8 and F9 genes coding regions, respectively, were included in this study. Our results indicate that even though DNA quality may be ideal for traditional DNA sequencing, enrichment techniques require more intact fragments, as reflected by variations in sequencing coverage between samples: quadruplicate results per sample showed 100X coverage varying from 80% of sequenced regions to less then 20%. Point substitutions found in F9 genes by Sanger sequencing were confirmed by targeted sequencing, but results for F8 gene were less satisfactory, in agreement with probe design limitations at this point. Of interest for hemophilia A patients, four samples possessed, in addition to the alterations in F8, point mutations in VWF. Probe design and sequencing parameters did not allow for the identification of F8 intron 1 and intron 22 inversions, frequent alterations in hemophilia A, but optimization procedures are currently underway. We conclude that targeted sequencing approach may be a viable and more complete solution for the diagnosis and management of hemophilia A, B and von Willebrand disease.