Dysfunctional C1 Inhibitor Research Articles

Clinical and laboratory spectrum of hereditary angioedema in a group of Egyptian children: a cross sectional study

BackgroundHereditary angioedema (HAE) is a hereditary illness represented by repeated bouts of submucosal or subcutaneous edema. Types of HAE includes; HAE with deficient C1-inhibitor (type 1), HAE with dysfunctional C1-inhibitor (type 2), and HAE with normal C1-inhibitor. Data on the epidemiology of HAE in Egypt are limited. Therefore, we aimed to characterize HAE in Egyptian children, identify the morbidity, and clarify HAE's different clinical and laboratory presentations.MethodsIn this cross-sectional study, we enrolled pediatric patients diagnosed with HAE according to the international hereditary angioedema WAO/EAACI guidelines. We gathered laboratory data on patients' mean serum C1 esterase inhibitor (C1-INH) level and activity, C4, and IgE levels.ResultsWe included 18 HAE patients (14 females and 4 males). They were between the ages of 6 and 18 years. The mean age upon confirmation of diagnosis was 8.4 ± 2.4 years. The mean time required to correctly diagnose HAE was 3.2 ± 1.8 years. We detected type I in 15 cases and type II in three cases. Eleven patients had a family member with HAE. In terms of previous misdiagnoses, 50% of patients were diagnosed with allergic angioedema. The median annual frequency of episodes was 17. The mean HAE attack time was 2.9 ± 1.5 days. Edema was most typically found in the face and abdomen. Trauma was the main triggering factor. We detected a significant direct relationship between severity of attack and C1-INH activity level.ConclusionsThis research adds a considerable clinical information about children with HAE. According to current results, there is a considerable underdiagnosis of HAE in Egypt. The detection and management of HAE can be improved by screening the relatives of HAE patients.

National survey on clinical and genetic characteristics of patients with hereditary angioedema in Latvia

BackgroundHereditary angioedema (HAE) is a rare and life-threatening inborn error of immunity. HAE is mostly caused by pathogenic variations in the serine protease inhibitor gene 1 (SERPING1), leading to deficient or dysfunctional C1-inhibitor (C1-INH), overproduction of bradykinin, and development of recurrent subcutaneous and/or submucosal oedema. The prevalence of HAE is 1 in 50,000 − 100000 people worldwide. We aimed to describe the clinical features and genetic spectrum of hereditary angioedema with C1-INH deficiency (C1-INH-HAE) in Latvia.MethodsAll patients from Latvia diagnosed with HAE (types I/II) from 2006 to March 2022 were included in the study. Laboratory tests and clinical data were analysed, and genetic tests with Sanger sequencing and whole genome sequencing were performed.ResultsThe study identified 10 C1-INH-HAE patients (nine females, one male) from eight families. The point prevalence of HAE in Latvia is 0.53 per 100 000 inhabitants. Of all patients, seven (70%) had HAE type I and three (30%) had HAE type II. The median age of patients was 54 years and the median age at onset of symptoms was 15 years. A significant delay (median 20.5 years) until diagnosis was observed, and 60% of patients had a positive family history of angioedema. All HAE patients have been hospitalised a median two times during their lifetime. Skin (100%), abdominal (80%), and airway (80%) oedema were the most frequent symptoms. Triggering factors (60%) and prodromal symptoms (90%) were referred. Attacks were severe in 50% of patients, moderate in 10%, and mild in 40%. Pathogenic variations of SERPING1 were identified in eight patients (six families), confirming the diagnosis molecularly. In two patients (two families), no pathogenic variations in the genes were found even after whole genome sequencing.ConclusionsCurrent data shows a significant delay and clear underdiagnosis of HAE in Latvia. Higher awareness and better information and communication between doctors would improve the diagnosis and management of HAE; as would screening of family members, patients with recurrent angioedema unresponsive to antihistamines and glucocorticoids, and patients with recurrent episodes of severe, unexplained abdominal pain.

Emergency room visits by patients with HAE based on data from the Canadian 2020 national survey

Introduction: Hereditary angioedema (HAE) is a genetic disorder resulting in low or dysfunctional C1 inhibitor (C1-INH): Type 1/2 HAE and/or dysregulation of bradykinin production: HAE with normal C1INH (HAEnC1-INH). HAE is characterized by recurring, painful swelling occurring in any part of the body. Laryngeal swelling can be fatal and abdominal swelling is very painful. Consequently, HAE patients often require emergency room (ER) visits.

Applying bioinformatic analysis for prognostic assessment of the <i>HS3ST6</i> missense mutations clinical significance in the development of hereditary angioedema

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.

A CASE OF HEREDITARY ANGIOEDEMA SUBTYPE SWITCH

<h3>Introduction</h3> Hereditary angioedema (HAE) is a condition that is described by recurrent episodes of edema without pruritis that can involve multiple different organ systems including skin, gastroenterological tract, and upper respiratory tract. HAE arises from deficiency or abnormality of C1 inhibitor (C1-INH). HAE can be classified into two different classes. HAE-type I is a deficiency in C1-INH resulting in low plasma protein and abnormal functional C1 esterase level. HAE-type II is a dysfunctional C1-INH resulting in low plasma protein but normal functional C1 esterase. <h3>Case Description</h3> A 54-year-old man presents to his primary care doctor's office with a longstanding history of intermittent abdominal pain and and facial swelling lasting 12-24 hours. He has been evaluated by multiple other specialists including Gastroenterologists without an official diagnosis. He was seen by an Allergist and was diagnosed with HAE- type II after his functional C1 esterase inhibitor was normal, C3 complement was low range, and C4 complement was low. He was diagnosed with lymphoma around the same time of his HAE-type II. He was treated with Danazol and his symptoms resolved. Shortly after, the repeat functional C1 esterase was much lower, C3 and C4 complement was still low. It had appeared that he was now consistent with HAE-type I. <h3>Discussion</h3> This HAE subtype switch has not yet been described in the medical community. HAE is condition that is still misdiagnosed amongst medical specialities given the lack of understanding despite it being commonly reported condition as it may mimic other IgE mediated reactions.

74 Hereditary angioedema revealed by compartment syndrome

BackgroundHereditary angioedema (HAE) can present with a wide spectrum of clinical symptoms, including articular features like the compartment syndrome.ObjectiveWe present the peculiar case of a young female patient suffering from this rare complement system disorder and presenting as a « wrist oedema ».MethodsA 14-year-old girl was admitted in the emergency room during a night shift. She presented with acute compartment (wrist) syndrome due to edematous compression of the median nerve, associated with a typical personal history of HAE. It resolved within 6 h with IV steroids and hyperhydration.The quantitative and qualitative C1 INH esterase returning negative, the diagnosis of HAE type III was made.The patient was treated with long-term treatment based on Danazol, (the most frequently prescribed attenuated androgen to treat HAE).ResultsHAE is due to the deficiency or dysfunction of the C1 inhibitor protein (quantitative or qualitative deficiency). A new nomenclature has replaced the initial use of denominations HAE type 1, 2 or 3; to speak rather of HAE with a deficient C1 inhibitor (type 1), with a dysfunctional C1 inhibitor (type 2) or with a normal C1 inhibitor (type 3)Type 3 HAE is rare and difficult to treat. It may respond to anti-estrogenic drugs such as progestins and especially to androgens; specific (very expensive) molecules do exist and act directly on the bradykinin pathwaysConclusionA compartment syndrome may reveal extremely rare conditions such as hereditary angioedema.Early recognition and management are the guarantee of a preserved functional prognosis.

The international WAO/EAACI guideline for the management of hereditary angioedema – The 2021 revision and update

Hereditary Angioedema (HAE) is a rare and disabling disease for which early diagnosis and effective therapy are critical. This revision and update of the global WAO/EAACI guideline on the diagnosis and management of HAE provides up-to-date guidance for the management of HAE. For this update and revision of the guideline, an international panel of experts reviewed the existing evidence, developed 28 recommendations, and established consensus by an online DELPHI process. The goal of these recommendations and guideline is to help physicians and their patients in making rational decisions in the management of HAE with deficient C1-inhibitor (type 1) and HAE with dysfunctional C1-inhibitor (type 2), by providing guidance on common and important clinical issues, such as: 1) How should HAE be diagnosed? 2) When should HAE patients receive prophylactic on top of on-demand treatment and what treatments should be used? 3) What are the goals of treatment? 4) Should HAE management be different for special HAE patient groups such as children or pregnant/breast feeding women? 5) How should HAE patients monitor their disease activity, impact, and control? It is also the intention of this guideline to help establish global standards for the management of HAE and to encourage and facilitate the use of recommended diagnostics and therapies for all patients.

The international WAO/EAACI guideline for the management of hereditary angioedema-The 2021 revision and update.

Hereditary angioedema (HAE) is a rare and disabling disease for which early diagnosis and effective therapy are critical. This revision and update of the global WAO/EAACI guideline on the diagnosis and management of HAE provides up-to-date guidance for the management of HAE. For this update and revision of the guideline, an international panel of experts reviewed the existing evidence, developed 28 recommendations, and established consensus by an online DELPHI process. The goal of these recommendations and guideline is to help physicians and their patients in making rational decisions in the management of HAE with deficient C1 inhibitor (type 1) and HAE with dysfunctional C1 inhibitor (type 2), by providing guidance on common and important clinical issues, such as: (1) How should HAE be diagnosed? (2) When should HAE patients receive prophylactic on top of on-demand treatment and what treatments should be used? (3) What are the goals of treatment? (4) Should HAE management be different for special HAE patient groups such as children or pregnant/breast-feeding women? and (5) How should HAE patients monitor their disease activity, impact, and control? It is also the intention of this guideline to help establish global standards for the management of HAE and to encourage and facilitate the use of recommended diagnostics and therapies for all patients.

Angioedema without wheals: a clinical update

Angioedema without wheals (urticaria) represents a heterogeneous group of clinically indistinguishable diseases of hereditary or acquired etiology. Hereditary angioedema is a rare inherited condition leading to recurrent, sometimes life-threatening angioedema attacks in subcutaneous tissues and gastrointestinal and oropharyngeal mucosa dating back to childhood or adolescence. Most of these patients have mutations in the SERPING1 gene, causing either low C1 inhibitor production (hereditary angioedema with C1 inhibitor deficiency type I) or the production of dysfunctional C1 inhibitor (hereditary angioedema with C1 inhibitor deficiency type II). Hereditary angioedema with normal C1 inhibitor has been defined later. Although C1 inhibitor concentration and function are in the normal range, it leads to typical hereditary angioedema symptoms owing to mutations in FXII, PLG, ANGPT1, KNG1, and MYOF genes. Patients who exhibit none of these genetic mutations despite having a similar clinical presentation are classified as having unknown hereditary angioedema. Fewer than 1 in 10 patients with C1 inhibitor deficiency have acquired angioedema with C1 inhibitor deficiency. The clinical presentation is very similar to that of hereditary angioedema, making it difficult to distinguish these 2 conditions clinically. Unlike hereditary angioedema, there are no genetic mutations, and family history and symptoms tend to appear later in life. Acquired angioedema with C1 inhibitor deficiency is commonly associated with lymphoproliferative and autoimmune diseases. Angioedema attacks might start 1 year before the underlying disease in acquired angioedema with C1 inhibitor deficiency. Approximately half of the patients admitted to the hospital for acute angioedema are patients receiving angiotensin-converting enzyme (ACE) inhibitor therapy. Angioedema typically occurs on the lips, tongue, mouth, pharynx, and subglottic regions. Patients may require hospitalization and intensive care monitoring owing to airway involvement. Idiopathic histaminergic acquired angioedema may be diagnosed only when any possible causes of histaminergic angioedema are excluded (foods, drugs, animal dander, aeroallergens, insect stings, latex, and others), and the symptoms respond well to antihistamine treatment. Idiopathic nonhistaminergic acquired angioedema should be considered when all other types of recurrent angioedema have been ruled out and patients do not respond to high-dose antihistamines. The lack of a standard biochemical laboratory test for patients with idiopathic histaminergic acquired angioedema, idiopathic nonhistaminergic acquired angioedema, angiotensin-converting enzyme inhibitor-induced acquired angioedema, and hereditary angioedema with normal C1 inhibitor makes the diagnosis more challenging. Future efforts should focus on increasing awareness of all the rare types of angioedema among physicians and developing more straightforward and more accessible diagnostic methods.

Hereditary angioedema caused by a premature stop codon mutation in the SERPING1 gene

BackgroundHereditary angioedema with deficient and dysfunctional C1 inhibitor (C1-INH-HAE) is a rare genetic disorder. The majority of the cases with this disease are caused by mutations in the C1-inbitor gene SERPING1 and are classified as type 1 and type 2. We aimed to detect mutations in the SERPING1 gene and evaluate its expression in nine probands with hereditary angioedema from nine different families.MethodsNine probands with hereditary angioedema from nine different families and 53 healthy controls were recruited in this study. All eight exons and intron–exon boundaries in the SERPING1 gene were amplified by PCR and then sequenced. Mutations were identified by alignment with reference sequences. mRNA expression was measured by real-time PCR.ResultsAll probands were diagnosed with HAE type 1. Nine mutations were found in nine patients: c.44delT, c.289C<T, c.296_303delCCATCCAA, c.538C<T, c.786_787insT, c.794 G < A, c.939delT, c.1214_1223delCCAGCCAGGA, and c.1279delC. All mutations formed a premature stop codon that might lead to the impaired synthesis of C1 inhibitor and result in the deficiency of this protein. None of the detected mutations were observed in the controls. In the C1-INH-HAE group, SERPING1 mRNA expression was significantly reduced (20% of the normal average level) compared to controls.ConclusionsThree known and six novel mutations in the SERPING1 gene were identified, and they produced a truncated nonfunctional C1 inhibitor without a reactive central loop. All the mutations led to reduced expression of SERPING1 mRNA in peripheral blood and low antigenic C1 inhibitor levels.

Oral Plasma Kallikrein Inhibitor BCX7353 for Treatment of Hereditary Angioedema

Hereditary angioedema (HAE) is rare disorder caused by a SERPING1 gene mutation that triggers severe swelling of the skin and upper airway. Treatment options for HAE with deficient and dysfunctional C1-inhibitor are expanding to include small-molecule drugs that inhibit protein interactions in the kallikrein-kinin system. Discovered by BioCryst Pharmaceuticals, BCX7353 is a synthetic, once-daily, small molecule drug that can be taken as an oral capsule to treat HAE attacks and for prophylaxis. This article will summarize recent and current BCX7353 clinical trials. Overall, results indicate BCX7353 is a promising form of therapy with a rapid 1 h onset of action, long duration of action, and acceptable tolerance.

Effect of an electronic treatment plan on acute management of hereditary angioedema

Hereditary angioedema (HAE) is a rare congenital disorder arising from decreased or dysfunctional complement C1 inhibitor (C1-INH),1 which manifests as painful, unpredictable, episodic swelling for which patients often present to the emergency department (ED). Edema of the face and oropharynx may be associated with life-threatening airway compromise, and abdominal swelling may be painful and debilitating. The latter may be associated with unnecessary surgeries or procedures,2-4 whereas airway and facial swelling is often mistaken for allergic or anaphylactic angioedema.

HAE Update: Determining optimal patient specific therapy

Hereditary angioedema (HAE) is a rare autosomal dominant disease caused by deficient or dysfunctional C1 inhibitor (C1 INH). HAE patients experience recurrent episodes of angioedema affecting the extremities, face, genitalia or submucosal edema in the abdomen or upper airway. Laryngeal attacks can be fatal. The determination of optimal therapy should be based on individualization of patient history and preferences. The parameters include attack frequency, location, severity and burden of illness on quality of life. Patients with HAE need medications for acute attacks; some also require prophylaxis. This is an overview of HAE treatments currently available in the US and how to individualize therapy for patients based on their circumstances. A literature search was performed for HAE and therapeutic modalities currently available. HAE guidelines and randomized, controlled clinical trials were evaluated. There are several options for acute and prophylactic treatment of HAE that have been approved by the Food and Drug Administration. Acute treatments include C1 INH, a replacement therapy; ecallantide, a kallikrein inhibitor; and icatibant, a bradykinin-2 receptor antagonist. Prophylactic treatments include attenuated androgens and C1 INH. These options have been proven safe and effective in clinical trials. Optimal therapy is based on the individual patients need regarding on-demand therapy and/or prophylactic therapy, short-term or long-term. Patients with HAE have individual requirements, based on the nature and frequency of past attacks, occupation, proximity to trained medical personnel, and patient preference. These factors should be used to create a patient-centered approach to management of HAE.

New treatment options for acute edema attacks caused by hereditary angioedema

New treatment options for acute edema attacks caused by hereditary angioedema (HAE) are reviewed. HAE is characterized by mutations in the C1 inhibitor gene leading to either a reduced expression of C1 inhibitor in the plasma or expression of a functionally impaired C1 inhibitor. HAE is classified into two major types based on the cause of the C1 inhibitor deficiency. Type I HAE is defined by a reduced expression of C1 inhibitor in the plasma, whereas type II HAE is characterized by the expression of a dysfunctional C1 inhibitor protein. Clinical data were reviewed for C1 inhibitor, ecallantide, and icatibant in the treatment of acute edema attacks caused by HAE. C1 inhibitor leads to a faster onset of edema relief and is effective in decreasing the duration of edema. Dosing strategies include fixed dosing and weight-based dosing. Optimal dosing strategies have not been established, but fixed dosing (500-1000 units) or 20 units/kg has been effective in clinical trials and reports. No comparative trials suggest that one strategy is superior to another; however, the approved labeling for acute treatment is based on weight. Ecallantide is also efficacious for treating acute episodes; however, the available evidence is limited to a single published trial. Icatibant has shown variable effects in two trials with placebo and active controls. In patients with HAE, most edema episodes only involve the skin and gastrointestinal tract, though airway obstruction caused by laryngeal angioedema is the most common cause of death. I.V. C1 inhibitor should be considered first-line treatment for acute edema attacks because of its fast onset of action and effectiveness, though it is not clear whether fixed or weight-based dosing is preferred. Ecallantide can be considered as a second-line treatment option.

Pharmacokinetic analysis of human plasma–derived pasteurized C1‐inhibitor concentrate in adults and children with hereditary angioedema: a prospective study

Hereditary angioedema (HAE) is a rare and potentially life-threatening disease presenting with acute edema of subcutaneous tissues and/or mucous membranes. Patients with HAE have abnormally low or dysfunctional C1-inhibitor (C1-INH). Preventing the progression of acute attacks is the main goal of C1-INH replacement therapy; knowledge of the C1-INH concentrate half-life is of crucial importance. This pharmacokinetic study was conducted to investigate the pharmacokinetics of pasteurized human plasma-derived C1-INH concentrate (pC1-INH). This was a prospective, single-center study of six children and 34 adults with an established diagnosis of HAE. On-demand treatment with pC1-INH was administered to all children, whereas adults received either pC1-INH on-demand treatment or individual replacement therapy (IRT). Functional C1-INH plasma levels were fitted to a single-compartment model with nonlinear regression, and the area under the curve was standardized to a dose equivalent of 15 U/kg body weight of pC1-INH concentrate. The median half-life of functional C1-INH plasma levels in pediatric patients receiving on-demand therapy was 32.9 hours (mean, 31.5 hr). In adults, the median half-lives of functional C1-INH plasma levels after on-demand therapy were 39.1 hours (mean, 47.8 hr) and 30.9 hours (mean 33.3 hr) for patients on IRT. The median times to achieve maximum plasma activity after administration were 0.6 hour for children, 1.0 hour for adults receiving on-demand treatment, and 0.5 hour for adults on IRT. pC1-INH concentrate has a long median terminal elimination half-life and rapidly reaches maximum plasma concentrations. This rapid onset of clinical efficacy is essential in patients suffering from HAE.

Appraisal of danazol prophylaxis for hereditary angioedema

Hereditary angioedema (HAE) is an autosomal dominant disease characterized by painful, recurrent attacks of inflammation affecting the hands, feet, face, abdomen, urogenital tract, and the larynx. The inflammation can be disfiguring, debilitating, quite painful, and, in the case of laryngeal attacks, life-threatening. Attacks are frequently the source of unnecessary exploratory abdominal procedures, extended hospital stays affecting a patient's ability to retain employment, and severe compromise of the patient's quality of life. HAE is estimated to affect 10,000 people in the US and is caused by deficient or dysfunctional C1-inhibitor, a naturally occurring molecule that is known to inhibit kallikrein, bradykinin, and other serine proteases in plasma. The treatment and management of HAE have been hampered by the dearth of safe and effective therapies. In the United States, there are currently no approved therapies for the treatment of acute HAE attacks. Although prophylactic HAE therapies do exist, they are often viewed as suboptimal due to moderate degrees of efficacy and the existence of adverse effects associated with therapy. Danazol, an attenuated androgen, is the most commonly prescribed prophylaxis treatment for HAE in the United States. Although it has demonstrated moderate efficacy in the prevention of HAE attacks, danazol's side-effect profile can be problematic because there is a correlation between frequency and severity of adverse events and dosage and duration of therapy.

Role of the P2 residue of complement 1 inhibitor (Ala443) in determination of target protease specificity: inhibition of complement and contact system proteases.

A dysfunctional C1 inhibitor (C1 INH) from a family in whom the propositus presented with systemic lupus erythematosus but without angioedema previously was shown to have diminished inhibitory activity toward isolated C1r and C1s, and intact C1. The mutation was identified as replacement of Ala443 (P2) with Val. This study further analyzed the reactivity of this mutant and characterized two mutants with Ser or Asp at this position. Ser at P2 does not interfere with binding of target proteases. However, the mutant with Asp at this position is unable to bind C1r and beta factor XIIa, and also has a decreased rate of reaction with C1s and kallikrein. Therefore, alteration of polarity alone had no effect on binding, while a bulky and/or charged side chain was not tolerated. Although defective in inhibition of C1r and C1s, the P2 A-->V mutant had acquired the ability to complex with trypsin. It also completely retained the ability to complex with kallikrein and factor XIIa. None of the 10 individuals expressing this mutant protein has ever had angioedema. This observation, combined with normal inhibition of contact system proteases and defective inhibition of complement proteases, suggests that angioedema is caused by bradykinin generated from contact system activation.

Characterization of C1 Inhibitor-Ta: A DYSFUNCTIONAL C1INH WITH DELETION OF LYSINE 251

Dysfunctional C1 inhibitor (C1INH)-Ta is a naturally occurring mutant from a patient with type II hereditary angioedema. This mutant has a deletion of the codon for Lys-251, which is located in the connecting strand between helix F and strand 3A, overlying beta sheet A. Deletion of this Lys modifies the amino acid sequence at this position from Asn-Lys-Ile-Ser to Asn-Ile-Ser and creates a new glycosylation site. To further characterize the mechanism of dysfunction, we have analyzed the recombinant normal and Ta proteins expressed by COS cells in addition to the proteins in serum and isolated from serum. Recombinant C1INH-Ta revealed an intermediate thermal stability in comparison with the intact and reactive center cleaved normal proteins. Analysis of the reactivity of this recombinant protein with target proteases demonstrated no complex formation with C1s, C1r, or kallikrein. Inefficient complex formation was, however, clearly detectable with beta-factor XIIa. Each protease produced partial cleavage of the recombinant mutant inhibitor. Recombinant C1INH-Ta, on 7.5% SDS-polyacrylamide gel electrophoresis and by size fractionation on Superose 12, showed a higher molecular weight fraction that was compatible in size with dimer formation. However, no multimerization of C1INH-Ta isolated from serum or of C1INH-Ta in serum, was observed. The C1INH-Ta dimer expressed the epitopes that normally are expressed only on the protease complexed or the cleaved inhibitor. These epitopes were not expressed on the monomeric inhibitor. The data suggest that the mutation in C1INH-Ta results in a folding abnormality that behaves as if it consists of two populations of molecules, one of which is susceptible to multimerization and one of which is converted to a substrate, but which retains residual inhibitory activity.

Unique C1 inhibitor dysfunction in a kindred without angioedema. I. A mutant C1 INH that inhibits C1-s but not C1-r.

We have described hereditary incomplete deficiency of the fourth component of complement (C4) in 10 members of a large kindred. C4 deficiency in this kindred is not linked to C4 loci in the HLA region. C4 synthesis is decreased, and C4 catabolism is normal in kindred members with low serum C4 levels. We have discovered a uniquely dysfunctional C1 inhibitor in all C4-deficient members of this kindred. C1 inhibitor dysfunction is revealed by incubating sera of affected members with EDTA, which destroys all C4 activity in these sera, but not in normal sera or sera from individuals with partial C4 deficiencies. The M(r) of C1 inhibitor purified from affected members is normal, but approximately 50% of this C1 inhibitor resists cleavage by trypsin (0.14 microM) at arg444, suggesting a substitution at this position. Moderate increases in trypsin, however, result in cleavage of the resistant molecules, which would not be expected if arg444 were the site of the mutation. All molecules in C1 inhibitor purified from affected members' plasma bind to activated C1s (C1-s), but approximately 50% of molecules in these preparations do not bind to activated C1r (C1r). These findings show that affected kindred members have a unique mutation in C1 inhibitor. The mutant C1 inhibitor does not prevent the activation of C1s by C1-r when serum Ca2+ is chelated by EDTA, but its inhibition of C1-s is normal in vivo, as shown by normal C2 levels, normal C4 catabolism, and absence of angioedema in C4-deficient members. The nature of the mutation, its selective failure to inhibit C1-r, and its relationship to decreased C4 synthesis remain to be defined.

A hinge region mutation in C1-inhibitor (Ala436–>Thr) results in nonsubstrate-like behavior and in polymerization of the molecule.

C1-inhibitor(Mo), a dysfunctional C1-inhibitor molecule produced in two kindred with type II hereditary angioedema, has a mutation at the P10 position (Ala436 to Thr). Like most serpins with hinge region mutations (P14, P12, P10), C1-inhibitor(Mo) loses its inhibitory activity. However, unlike the other hinge region mutations, this mutant is not converted to a substrate. As shown by nondenaturing gel electrophoresis, gel filtration, sucrose density gradient ultracentrifugation, and electron microscopy, C1-inhibitor(Mo) exists in both monomeric and multimeric forms. Polymerization probably results from reactive center loop insertion into the A sheet of an adjacent molecule. Native C1-inhibitor(Mo) was shown to have a thermal stability profile intermediate to those of intact and of cleaved normal C1-inhibitor. Native C1-inhibitor(Mo) did not bind to monoclonal antibody KII, which binds only to reactive center-cleaved normal C1-inhibitor. It did, however, react with monoclonal antibody KOK12, which recognizes complexed or cleaved C1-inhibitor but not intact normal C1-inhibitor. Native C1-inhibitor(Mo), therefore, exists in a conformation similar to the complexed form of normal C1-inhibitor.