SERPING1 Variants and C1-INH Biological Function: A Close Relationship With C1-INH-HAE.

Hereditary angioedema with C1 Inhibitor deficiency (C1-INH-HAE) is caused by a constellation of variants of the SERPING1 gene (n = 809; 1,494 pedigrees), accounting for 86.8% of HAE families, showing a pronounced mutagenic liability of SERPING1 and pertaining to 5.6% de novo variants. C1-INH is the major control serpin of the kallikrein-kinin system (KKS). In addition, C1-INH controls complement C1 and plasminogen activation, both systems contributing to inflammation. Recognizing the failed control of C1s protease or KKS provides the diagnosis of C1-INH-HAE. SERPING1 variants usually behave in an autosomal-dominant character with an incomplete penetrance and a low prevalence. A great majority of variants (809/893; 90.5%) that were introduced into online database have been considered as pathogenic/likely pathogenic. Haploinsufficiency is a common feature in C1-INH-HAE where a dominant-negative variant product impacts the wild-type allele and renders it inactive. Small (36.2%) and large (8.3%) deletions/duplications are common, with exon 4 as the most affected one. Point substitutions with missense variants (32.2%) are of interest for the serpin structure-function relationship. Canonical splice sites can be affected by variants within introns and exons also (14.3%). For noncanonical sequences, exon skipping has been confirmed by splicing analyses of patients' blood-derived RNAs (n = 25). Exonic variants (n = 6) can affect exon splicing. Rare deep-intron variants (n = 6), putatively acting as pseudo-exon activating mutations, have been characterized as pathogenic. Some variants have been characterized as benign/likely benign/of uncertain significance (n = 74). This category includes some homozygous (n = 10) or compound heterozygous variants (n = 11). They are presenting with minor allele frequency (MAF) below 0.00002 (i.e., lower than C1-INH-HAE frequency), and may be quantitatively unable to cause haploinsufficiency. Rare benign variants could contribute as disease modifiers. Gonadal mosaicism in C1-INH-HAE is rare and must be distinguished from a de novo variant. Situations with paternal or maternal disomy have been recorded (n = 3). Genotypes must be interpreted with biological investigation fitting with C1-INH expression and typing. Any SERPING1 variant reminiscent of the dysfunctional phenotype of serpin with multimerization or latency should be identified as serpinopathy.

SERPING1 mutation update: Mutation spectrum and C1 Inhibitor phenotypes.

C1 inhibitor (C1Inh) deficiency is responsible for hereditary angioedema (C1-INH-HAE) and caused by variants of the SERPING1/C1INH/C1NH gene. C1Inh is the major control of kallikrein-kinin system. C1Inh deficiency leads to its uncontrolled activation, with subsequent generation of the vasoactive peptide bradykinin. This update documents 748 different SERPING1 variants, including published variants and additional 120 unpublished ones. They were identified as heterozygous variants (n = 729), as homozygous variants in 10 probands and as compound heterozygous variants (nine combinations). Six probands with heterozygous variants exhibited gonadal mosaicism. Probands with heterozygous (n = 72) and homozygous (n = 1) variants were identified as de novo cases. Overall, 58 variants were found at positions showing high residue conservation among serpins, and have been referred to as a mousetrap function of C1Inh: reactive center loop, gate, shutter, breach, and hinge. C1Inh phenotype analysis identified dysfunctional serpin variants with failed serpin-protease association and a residual 105-kDa species after incubation with target protease. Regarding this characteristic, in conditions with low antigenic C1Inh, 74 C1-INH-HAE probands presented with an additional so-called intermediate C1-INH-HAE phenotype. The present update addresses a comprehensive SERPING1 variant spectrum that facilitates genotype-phenotype correlations, highlighting residues of strategic importance for serpin function and for identification of C1Inh deficiency as serpinopathy.

Hereditary C1 inhibitor deficiency is associated with high spontaneous amidase activity.

BACKGROUND: Angioedema diagnosis classically targets the complement system (via C1 inhibitor (C1Inh) function and antigenic C4 level) and contact phase activation (via amidase activity). Bradykinin is responsible for angioedema attacks and is produced from contact phase activation secondary to failed C1Inh control. OBJECTIVE: We aimed to compare the diagnostic performances of spontaneous amidase activity and antigenic C4 level in C1Inh hereditary angioedema (C1Inh-HAE) patients. METHODS: Samples from 185 C1Inh-HAE patients (81 men, 104 women; confirmed by SERPING1 gene mutations) and from 99 blood donors (50 men, 49 women) were tested for C1Inh function, antigenic C4 level and spontaneous amidase activity. RESULTS: In the C1Inh-HAE group, antigenic C4 level was decreased (n=135) and amidase activity was increased (n=181). Receiver operating characteristic analyses showed higher diagnostic performance values for the spontaneous amidase assay compared to those of antigenic C4. CONCLUSION: The spontaneous amidase activity assay should replace antigenic C4 level testing and should be tested alongside the C1Inh function for both AE screening and follow up of HAE patients.

A nationwide study of acquired C1-inhibitor deficiency in France: Characteristics and treatment responses in 92 patients.

Acquired angioedema (AAE) due to C1-inhibitor (C1INH) deficiency is rare. Treatment options for acute attacks are variable and used off-label. Successful treatment of the associated lymphoma with rituximab seems to prevent acute attacks in subjects with AAE. The aim of this study was to describe AAE manifestations, its associated diseases, and patients' responses to treatments in a representative cohort.A retrospective nationwide study was conducted in France. The inclusion criteria were recurrent angioedema attacks and an acquired decrease in functional C1INH <50% of the reference value.A total of 92 cases were included, with a median age at onset of 62 years. Facial edema and abdominal pain were the most frequent symptoms. Fifteen patients were hospitalized in the intensive care unit because of laryngeal edema, and 1 patient died. Anti-C1INH antibodies were present in 43 patients. The associated diseases were primarily non-Hodgkin lymphoma (n = 44, with 24 splenic marginal zone lymphomas) and monoclonal gammopathy of undetermined significance (n = 24). Three patients had myeloma, 1 had amyloid light-chain (of immunoglobulin) (AL) amyloidosis, 1 patient had a bronchial adenocarcinoma, and 19 patients had no associated disease. Icatibant relieved the symptoms in all treated patients (n = 26), and plasma-derived C1INH concentrate in 19 of 21 treated patients. Six patients experienced thromboembolic events under tranexamic acid prophylaxis. Rituximab prevented angioedema in 27 of 34 patients as a monotherapy or in association with chemotherapy. Splenectomy controlled AAE in 7 patients treated for splenic marginal zone lymphoma. After a median follow-up of 4.2 years, angioedema was on remission in 52 patients.AAE cases are primarily associated with indolent lymphoma-especially splenic marginal zone lymphoma-and monoclonal gammopathy of undetermined significance but not with autoimmune diseases or other conditions. Icatibant and plasma-derived C1INH concentrate control attacks; splenectomy and immunochemotherapy prevent angioedema in lymphoma setting.

Phospholipase A2 Receptor-Related Membranous Nephropathy and Mannan-Binding Lectin Deficiency.

Most patients with idiopathic membranous nephropathy (IMN) have IgG4 autoantibodies against phospholipase A2 receptor (PLA2R). C3 and C5b-9 are found in immune deposits of IMN kidney biopsy specimens, but the pathway of complement activation in IMN remains elusive. We report the case of a patient who developed IMN with intense staining for PLA2R, IgG4, C3, C5b-9, factor B, and properdin and very weak staining for C1q, C4d, and IgG1. Measurement of mannan binding lectin (MBL) antigenic level and activity revealed MBL deficiency. Genotyping revealed a heterozygous (A/C) polymorphism in codon 57 of MBL2 exon 1 associated with homozygous and heterozygous variations in the promoter region at -550 (L/L) and -221 (X/Y), respectively, suggesting that the patient harbored the LXA/LYC haplotypes linked to MBL deficiency. Genetic sequencing in 77 consecutive patients with IMN identified four patients with MBL2 promoter and coding region variations associated with MBL deficiency and the same complement pattern in immune deposits as the index patient. In contrast, patients with wild-type MBL2 had immune deposits with intense Cd4 staining. Thus, IMN can develop in patients with complete MBL deficiency, with complement activated mainly by the alternative pathway, whereas the lectin pathway is also activated in those with wild-type MBL2.

C1 Inhibitor as a glycoprotein: The influence of polysaccharides on its function and autoantibody target.

C1 Inhibitor (C1Inh), a member of the Serine proteinase inhibitor family, is the most heavily glycosylated plasma protein. This work investigated the impact of C1Inh glycosylation on its function regarding protease targets and autoantibody binding. C1Inh deglycosylation was found to affect its function with O-linked polysaccharides, but not with N-linked polysaccharides, in controlling the contact phase but not C1s target, thus indicating the N-terminal domain's involvement in C1Inh function. Instructive samples demonstrated that O-deglycosylation strongly suppressed autoantibody binding, suggesting the polysaccharide motif is an antibody target. The autoantibodies did not directly affect C1Inh function.

Coagulation Factor XII Gene Mutation in Brazilian Families with Hereditary Angioedema with Normal C1 Inhibitor.

BACKGROUND: Hereditary angioedema (HAE) with normal C1 inhibitor (C1-INH) is a rare disorder. Mutations of the gene encoding coagulation factor XII have been identified in a subset of patients with this condition. Our aim was to investigate mutations in the F12 gene in patients with HAE with normal C1-INH from Brazil. METHODS: We studied 5 Brazilian families with index female patients who presented with recurrent angioedema with normal C1-INH and C4 levels. Genomic DNA was isolated from whole blood and PCR was performed. Mutations were detected by the sequencing of exon 9 of the F12 gene and allelic discrimination. RESULTS: The c.983C>A (p.Thr328Lys) mutation was identified in 16 subjects, from 4 of the 5 families studied, including 8 patients with symptoms of HAE with normal C1-INH (87.5% women) and 8 subjects asymptomatic for HAE (25% women). Mean age at onset of symptoms among the FXII-HAE patients was 13.8 years (range 6-25 years). Recurrent abdominal pain (100%) and subcutaneous angioedema (87.5%) were the most frequent clinical presentations. Two patients presented with associated laryngeal edema. In keeping with previous observations in patients with both C1-INH-HAE and HAE with normal C1-INH, all 7 women with FXII-HAE reported triggering or worsening of symptoms upon intake of estrogen-containing oral contraceptives and/or pregnancy. CONCLUSIONS: We report for the first time in Brazil a mutation in the F12 gene as a likely cause of HAE with normal C1-INH in patients with recurrent attacks of angioedema and/or abdominal pain. A higher frequency of abdominal pain attacks and onset of symptoms at a younger age were observed among Brazilian patients when compared to those from other parts of the world.

Distinct conditions support a novel classification for bradykinin-mediated angio-oedema.

BACKGROUND: Angio-oedema (AO) can be attributable to bradykinin (BK) accumulation, as is the case for prototypical hereditary AO (HAO) due to C1 inhibitor (C1-INH) deficiency. However, our clinical experience in a reference centre has shown that some patients display a clinical history suggestive of HAO, but exhibit normal C1-INH function, have no mutation in the causative genes associated with HAO (SERPING1, F12), and report no intake of drugs known to promote AO. OBJECTIVE: We sought to determine the frequency and distribution of different AO subtypes suspected to be BK-mediated AO (BK-AO) and defined by clinical, history and biological criteria (enzyme activities implicated in BK formation and catabolism). METHODS: The files of all patients referred to our centre for suspected BK-AO were retrospectively analysed. RESULTS: The distribution of patients (n = 162) was 16 and 4% with a hereditary deficiency of C1-INH or a gain of factor XII function, respectively, 29% with iatrogenic BK-AO, 21% with non-iatrogenic defective kininase activity and 30% with idiopathic increased kinin formation. CONCLUSION: BK-AO may be caused by multiple inherited or acquired factors triggering BK accumulation. Therefore, we propose a novel typology for BK-AO based on the imbalance of production/catabolism of BK.

[Hereditary angioedema biological diagnosis]. / Angiœdème héréditaire: diagnostic biologique.

C1 inhibitor (C1 Inh) activity is an essential parameter for kinins angioedema (AE) diagnosis either hereditary or acquired or sporadic, it is analysed on plasma exclusively. Hereditary AE with C1 Inh functional deficiency is associated with alterations of the SERPING1 gene. Hereditary AE with normal C1 Inh (HAE nC1 Inh) is combined with F12 gene mutations, it is coding for Factor XII whose activity is controlled by C1 Inh, they are found in about 5% of HAE nC1 Inh cases. Every loss of C1 Inh activity must be taken as anormal by clinicians even for women with oral oestroprogestatives, it would be confirmed by the presence of cleaved C1 Inh. The kinins (primarily bradykinin) are the mediators responsible for local increase of vascular permeability. Bradykinin is released from high MW kininogen (HK) during the contact system activation. Plasma proteases mainly support this proteolytic activity controlled by C1 Inh. Family of a patient diagnosed with HAE must be studied, symptomatic as asymptomatic members indeed clinical symptoms regularly emerge very late in the life.

Enzymatic assays for the diagnosis of bradykinin-dependent angioedema.

BACKGROUND: The kinins (primarily bradykinin, BK) represent the mediators responsible for local increase of vascular permeability in hereditary angioedema (HAE), HAE I-II associated with alterations of the SERPING1 gene and HAE with normal C1-Inhibitor function (HAE-nC1INH). Besides C1-Inhibitor function and concentration, no biological assay of kinin metabolism is actually available to help physicians for the diagnosis of angioedema (AE). We describe enzymatic tests on the plasma for diagnosis of BK-dependent AE. METHODS: The plasma amidase assays are performed using the Pro-Phe-Arg-p-nitroanilide peptide substrate to evaluate the spontaneous amidase activity and the proenzyme activation. We analyzed data of 872 patients presenting with BK-dependent AE or BK-unrelated diseases, compared to 303 controls. Anti-high MW kininogen (HK) immunoblot was achieved to confirm HK cleavage in exemplary samples. Reproducibility, repeatability, limit of blank, limit of detection, precision, linearity and receiver operating characteristics (ROC) were used to calculate the diagnostic performance of the assays. RESULTS: Spontaneous amidase activity was significantly increased in all BK-dependent AE, associated with the acute phase of disease in HAE-nC1INH, but preserved in BK-unrelated disorders. The increase of the amidase activity was associated to HK proteolysis, indicating its relevance to identify kininogenase activity. The oestrogens, known for precipitating AE episodes, were found as triggers of enzymatic activity. Calculations from ROC curves gave the optimum diagnostic cut-off for women (9.3 nmol⋅min(-1)⋅mL(-1), area under curve [AUC] 92.1%, sensitivity 80.0%, and specificity 90.1%) and for men (6.6 nmol·min(-1)⋅mL(-1), AUC 91.0%, sensitivity 87.0% and specificity 81.2%). CONCLUSION: The amidase assay represents a diagnostic tool to help physicians in the decision to distinguish between BK-related and -unrelated AE.

Complement alternative pathway activation in the course of thrombotic microangiopathy associated with adult-onset Still's disease.

Atypical haemolytic uraemic syndrome is a rare disease associated which genetic or acquired factors those cause defective regulation of the alternative complement pathway. We report the case of a 46-year-old woman who presented with thrombotic microangiopathy coinciding with a monocyclic evolution of adult-onset Still's disease. Low C3 with decreased FB concentration, associated with normal C4 was present until the thrombotic microangiopathy's resolution, indicative of an excessive production of alternative C3 convertase. She responded to plasma exchange. This observation reinforces the hypothesis for a common pathway in the pathogenesis for both of the diseases, and suggests alternative complement pathway mediation.

Acquired C1-inhibitor deficiency: 7 patients treated with rituximab.

BACKGROUND: Acquired C1-inhibitor deficiency can occur secondary to excessive C1-inhibitor consumption (type I) and be associated with a lymphoid hemopathy, or linked to the presence of anti-C1-inhibitor autoantibodies (type II) in a context of an isolated monoclonal gammopathy, sometimes associated with lymphoproliferation. Efficacy of danazol, tranexamic acid and/or corticosteroids is inconstant. Rituximab efficacy against type II angioedema has been reported. METHODS: Description of 7 rituximab-treated patients, 6 with type II acquired angioedema and 1 with type I. RESULTS: Clinical efficacy (only for type II) was complete for 3, partial for 2 and 2 were therapeutic failures. Only 2 patients had improved biological parameters, with normalization of their C1-inhibitor levels and diminished anti-C1-inhibitor autoantibodies, observed 1-9 months after the last infusion of the second rituximab cycle. An associated lymphoproliferation did not affect the response to treatment. CONCLUSION: Rituximab efficacy in the treatment of acquired angioedema is inconstant and might require repeated cycles.

Human C3 deficiency associated with impairments in dendritic cell differentiation, memory B cells, and regulatory T cells.

Primary C3 deficiency, a rare autosomal inherited disease (OMIM 120700), was identified in a 2-year-old male suffering from recurrent pyogenic infections from early infancy with undetectable total complement hemolytic activity (CH50) and C3 values. The nonconsanguineous parents and the two patients' two siblings had 50% normal serum C3 concentration. The molecular abnormality associated a paternal allele coding C3 with the missense mutation p.Ser(550)Pro and an apparently null maternal allele, with production of a defective protein that could no longer be secreted. Vaccination of the child did not induce a long-term Ab response. Accordingly, switched memory IgD(-)CD27(+) B cells were barely detected, amounting to only 2.3% of peripheral blood CD19(+) cells. Cells were significantly defective in stimulating alloreactive responses. The in vitro development of immature dendritic cells and their maturation capacity were greatly impaired, with decreased CD1a expression and IL-12p70 secretion ability. These cells were unable to induce autologous B cell proliferation and Ig secretion in the presence of CD40L and C3. Finally, the regulatory T cell development ability of CD4(+) T cells after CD3 and CD46 activation in the presence of IL-2 was significantly impaired. Thus, the association of important functional defects of dendritic cells, acquisition of B cell memory, and regulatory T cells with human C3 deficiency strongly supports a major role for C3 in bridging innate and adaptive immunity in humans.

Functional C1-inhibitor diagnostics in hereditary angioedema: assay evaluation and recommendations.

Hereditary angioedema (HAE) is an autosomal dominant disease characterized by recurrent episodes of potentially life-threatening angioedema. The most widespread underlying genetic deficiency is a heterozygous deficiency of the serine protease inhibitor C1 esterase inhibitor (C1-Inh). In addition to low C4 levels, the most important laboratory parameter for correct diagnosis of HAE or angioedema due to acquired C1-Inh deficiency is reduced C1-Inh function (fC1-Inh). No direct recommendations about the assays for fC1-Inh or sample handling conditions are available, although this would prove especially useful when a laboratory first starts to offer assays on fC1-Inh for HAE diagnosis. In the present study we evaluated the performance of fC1-Inh assays in the 15 different laboratories that are specialised in HAE diagnostics and assessed inter-laboratory variation with each laboratory using their own assays and standards. A double-blind survey was conducted using plasma/serum samples from healthy donors and HAE patients and the uniformity of HAE diagnosis was evaluated. It can be concluded that the diagnosis of fC1-Inh deficiency was made correctly in most cases in this survey. We can recommend the chromogenic assay for the determination of fC1-Inh, while the complex ELISA needs further investigation.

Disease expression in women with hereditary angioedema.

OBJECTIVE: Fluctuations in sex hormones can trigger angioedema attacks in women with hereditary angioedema. Combined oral contraceptive therapies, as well as pregnancy, can induce severe attacks. The course of angioedema may be very variable in different women. STUDY DESIGN: Within the PREHAEAT project launched by the European Union, data on 150 postpubertal women with hereditary angioedema were collected in 8 countries, using a patient-based questionnaire. RESULTS: Puberty worsened the disease for 62%. Combined oral contraceptives worsened the disease for 79%, whereas progestogen-only pills improved it for 64%. During pregnancies, 38% of women had more attacks, but 30% had fewer attacks. Vaginal delivery was usually uncomplicated. Attacks occurred within 48 hours in only 6% of cases. Those more severely affected during menses had more symptoms during pregnancies, suggesting a hormone-sensitive phenotype for some patients. CONCLUSION: The course of angioedema in women with C1 inhibitor deficiency is affected by physiologic hormonal changes; consequently, physicians should take these into account when advising on management.