Hereditary angioedema (HAE) is a genetically determined disease characterized by recurrent attacks of edema affecting the subcutaneous and/or submucosal layers of tissue, face, lips, neck, extremities of the body, oral cavity, intestine and/or larynx. In the latter case, the disease becomes life-threatening. The majority of HAE cases are associated with decreased levels of C1 (C1-esterase inhibitor), there are also descriptions of HAE with dysfunctional C1 inhibitor and HAE with normal C1 inhibitor. In the first and second variants, mutations in the C1NH gene are the cause of the disease. HAE with normal quantitative and functional levels of C1-inhibitor has the same clinical manifestations but with mutations in other genes, including F12, PLG, ANGPT1, KNG1, MYOF, and HS3ST6. Currently, mutations in the HS3ST6 gene remain poorly understood; only one missense mutation (p.Thr144Ser, rs746467957) associated with the development of HAE has been described.The aim of our work was to study new mutations in the HS3ST6 gene and analyze in silico their prognostic nature and clinical significance for the development of hereditary angioedema.The material was whole blood samples obtained from 13 patients with symptoms of hereditary angioedema without reduced levels and function of C1-INH.Whole exome sequencing of patients, bioinformatic analysis of HS3ST6 gene mutations using a number of databases and Web resources to predict the effect of mutations on the protein and assess the conservatism of the positions of the mutations detected was involved in study methods.Mutations in the HS3ST6 gene were identified in four patients, including two cases with two mutations simultaneously. Application of bioinformatic analysis allowed us to obtain new data on four missense mutations in the studied gene. Potential pathogenetic significance was determined for three of them. The mutation NC_000016.9:g.1962132G>A (p.A163V) is most likely to be involved in pathogenesis of HAE by indirect disruption of heparan sulfate O-sulfation directly within the protein. The NC_000016.9:g.1962024G>A mutation (p.P199L) appears to lead to the development of the disease through disruption of docking with SDC2 heparan sulfate. In the NC_000016.9:g.1962046C>T (p.A192T) mutation, destabilization of the 192 amino acid position next to PAPS, may contribute to disruption of heparan sulfate O-sulfation through disruption of protein functional activity and, therefore, catalysis transfer of sulfo group to heparan sulfate syndecan-2. Thus, in all three cases, the formation of HAE appears to be possible due to disruption of the O-sulfation steps of heparan sulfate syndecan-2.Considering that in silico methods offer new opportunities to assess the pathogenetic significance of mutations, the application of bioinformatic analysis can contribute to a detailed investigation of the causes of hereditary angioedema. The present work convincingly demonstrates that rare mutations in the HS3ST6 gene may be involved in the pathogenesis of HAE and provoke edema due to increased bradykinin release.
