Genetic Screening in Patients Suspected of Inherited Bleeding Disorders

Sammanfattning: Inherited bleeding disorders constitute a heterogeneous group of genetic diseases, affecting virtually all major components of the hemostatic system. The diagnostics are potentially complex, and a high proportion of patients remain without a conclusive diagnosis following work-up. In recent years, advances in high-throughput DNA sequencing technologies have facilitated the use of genetic investigations in patients suspected of inherited bleeding disorders. Even though genetic investigations have contributed appreciably to the diagnostics, a considerable proportion of the genetic variants identified are still of uncertain significance. The overall aim of this thesis was to investigate the significance of selected genetic variants identified in patients suspected of inherited bleeding disorders, presenting with incompletely explained bleeding tendencies. In Paper I, the consequences of heterozygous variants in the genes UNC13D, STX11 and STXBP2 were investigated by functional methods. The results suggested an association between heterozygous variants in UNC13D, STX11 or STXBP2 and impaired platelet degranulation, possibly contributing to increased bleeding in affected patients. In Paper II, a rare variant in FGB was identified as the cause of familial hypofibrinogenemia following genetic and functional investigations. In Paper III, investigations using biomarkers specific for collagen formation and degradation were not able to verify any functional abnormalities hypothesized to result from heterozygous variants in COL1A1, COL3A1, COL5A1 or COL5A2. However, an interesting negative correlation between plasma ascorbic acid levels and the ISTH-BAT bleeding score was observed in the patients. In Paper IV, two previously undescribed variants in GNE were found to be causative of severe congenital macrothrombocytopenia when harbored in a compound heterozygous state, as a result of markedly decreased platelet sialylation. Treatment with the sialidase inhibitor oseltamivir did not prove to be effective for increasing the platelet counts. In summary, this thesis contributes to the continuously increasing knowledge of genetic variants associated with inherited bleeding disorders, required for adequately diagnosing a higher proportion of patients suffering from constitutionally increased bleeding.