Phenotypic and molecular characterization of the largest worldwide cluster of hereditary angioedema type 1

Abstract

Hereditary angioedema type 1 (HAE1) is a rare, genetically heterogeneous, and autosomal dominant disease. It is a highly variable, insidious, and potentially life-threatening condition, characterized by sudden local, often asymmetric, and episodic subcutaneous and submucosal swelling, caused by pathogenic molecular variants in the SERPING1 gene, which codes for C1-Inhibitor protein. This study performed the phenotypic and molecular characterization of a HAE1 cluster that includes the largest number of affected worldwide. A geographically HAE1 cluster was found in the northeast Colombian department of Boyaca, which accounts for four unrelated families, with 79 suspected to be affected members. Next-Generation Sequencing (NGS) was performed in 2 out of 4 families (Family 1 and Family 4), identifying the variants c.1420C>T and c.1238T>G, respectively. The latter corresponds to a novel mutation. For Families 2 and 3, the c.1417G>A variant was confirmed by Sanger sequencing. This variant had been previously reported to the patient prior to the beginning of this study. Using deep-learning methods, the structure of the C1-Inhibitor protein, p.Gln474* and p.Met413Arg was predicted, and we propose the molecular mechanism related to the etiology of the disease. Using Sanger sequencing, family segregation analysis was performed on 44 individuals belonging to the families analyzed. The identification of this cluster and its molecular analysis will allow the timely identification of new cases and the establishment of adequate treatment strategies. Our results establish the importance of performing population genetic studies in a multi-cluster region for genetic diseases.

Fig 1

SERPING1 variant on Family 1 A) Pedigree of Family 1 with persons harboring the variant c.1420C>T p.(Gln474*) and Sanger sequencing confirmation of IV,38 and IV,41.+WES and *or ** negative or positive SS respectively. B) Left, the wild-type SERPING1 protein structure with the reactive center loop (RCL) highlighted in magenta. The central beta-sheet region is indicated in red; right, SERPING1 protein structure featuring the Gln474* variant. The molecular variant promotes the insertion of the RCL into the central beta-sheet, mimicking the latent form of the protein. The absence of the RCL region is shown, and the central beta-sheet is indicated in red. The overall conformational change depicts the predicted structural transition associated with the pathogenic variant.

Fig 2. SERPING1 variants on Family 2 and 3.

A) and B) Pedigrees of Family 2 and with persons harboring the variant c.1417G>A p.Val473Met and the Sanger Sequencing confirmation of Family 2 IV,2 and Family 3 IV,11. *or ** negative or positive SS respectively.

Fig 3

SERPING1 variants on Family 4 A) Pedigree of Family 4 with persons harboring the variant c.1238T>G p.(Met413Arg) and the Sanger Sequencing confirmation of the Family 4 III,4..+WES and *or ** negative or positive SS respectively B) and C) DynaMut2 protein stability change predictions (ΔΔGstability) were determined by uploading the experimentally derived structure of C1-inhibitor protein to the DynaMut2 server at https://biosig.lab.uq.edu.au/dynamut2/. Dashed lines predict intramolecular interactions. Predicted hydrophobic interactions are shown in green, intramolecular clashes in pink, hydrogen bonds in orange, and carbonyl interactions in blue. (A-B) WT C1-inhibitor protein, (C-D) Met413Arg C1-inhibitor protein.