The Expanding Spectrum of Mutations in Hereditary Angioedema

The CC2D2B is a novel genetic modifier of the clinical phenotype in patients with hereditary angioedema due to C1 inhibitor deficiency

Hereditary angioedema due to C1 inhibitor deficiency (HAE-C1-INH) is a rare genetic disorder caused by pathogenic variants in the SERPING1 gene and characterised by swelling and a highly variable clinical phenotype. We aimed to identify novel modifying genetic factors predisposing to the clinical symptoms. We performed whole exome sequencing (WES) and comprehensive bioinformatic analysis in symptomatic and asymptomatic (three duos) family members with HAE-C1-INH. Selected variants identified using WES (present in all asymptomatic and absent in symptomatic patients) were determined using Sanger sequencing. We included 88 clinically well-characterised HAE-C1-INH patients from south-eastern Europe (nine asymptomatic) from 42 unrelated families. We identified 39 variants in 23 genes (ANKRD36C, ARGFX, CC2D2B, IL5RA, IRF2BP2, LGR6, MRPL45, MUC3A, NPIPA1, NRG1, OR5M1, OR5M3, OR5M10, OR8U3, PLCL1, PRSS3, PSKH2, PTPRA, RTP4, SEZ6, SLC25A5, VWA3A, and ZNF790). We selected variants in CC2D2B and PLCL1, which were analysed using Sanger sequencing in the entire group of HAE-C1-INH. We found significant differences in the frequencies of the CC2D2B c.190A>G (rs17383738) variant between symptomatic and asymptomatic patients, where heterozygotes were more common in asymptomatic HAE-C1-INH patients in comparison to symptomatic patients (55 % vs 23%; P = 0.049, OR = 4.24, 95% CI 1.07-14.69). Our study identified novel genetic factors that modify the clinical variability of HAE-C1-INH. We further demonstrated, in a large cohort, the importance of the CC2D2B gene as a disease-modifying factor. Based on linkage disequilibrium analysis, the CCNJ and ZNF518A genes might also be involved in the clinical variability of HAE-C1-INH.

Definition, acronyms, nomenclature, and classification of angioedema (DANCE): AAAAI, ACAAI, ACARE, and APAAACI DANCE consensus

BACKGROUND

Angioedema (AE) manifests with intermittent, localized, self-limiting swelling of the subcutaneous and/or submucosal tissue. AE is heterogeneous, can be hereditary or acquired, may occur only once or be recurrent, may exhibit wheals or not, and may be due to mast cell mediators, bradykinin, or other mechanisms. Several different taxonomic systems are currently used, making it difficult to compare the results of studies, develop multicenter collaboration, and harmonize AE treatment.

OBJECTIVE

We developed a consensus on the definition, acronyms, nomenclature, and classification of AE (DANCE).

METHODS

The initiative involved 91 experts from 35 countries and was endorsed by 53 scientific and medical societies, and patient organizations. A consensus was reached by online discussion and voting using the Delphi process over a period of 16 months (June 2021 to November 2022).

RESULTS

The DANCE initiative resulted in an international consensus on the definition, classification, and terminology of AE. The new consensus classification features 5 types and endotypes of AE and a harmonized vocabulary of abbreviations/acronyms.

CONCLUSION

The DANCE classification complements current clinical guidelines and expert consensus recommendations on the diagnostic assessment and treatment of AE. DANCE does not replace current clinical guidelines, and expert consensus algorithms and should not be misconstrued in a way that affects reimbursement of medicines prescribed by physicians using sound clinical judgment. We anticipate that this new AE taxonomy and nomenclature will harmonize and facilitate AE research and clinical studies, thereby improving patient care.

Meta-analysis of ACE inhibitor-induced angioedema identifies novel risk locus

BACKGROUND

Angioedema is a rare but potentially life-threatening adverse drug reaction in patients receiving angiotensin-converting enzyme inhibitors (ACEis). Research suggests that susceptibility to ACEi-induced angioedema (ACEi-AE) involves both genetic and nongenetic risk factors. Genome- and exome-wide studies of ACEi-AE have identified the first genetic risk loci. However, understanding of the underlying pathophysiology remains limited.

OBJECTIVE

We sought to identify further genetic factors of ACEi-AE to eventually gain a deeper understanding of its pathophysiology.

METHODS

By combining data from 8 cohorts, a genome-wide association study meta-analysis was performed in more than 1000 European patients with ACEi-AE. Secondary bioinformatic analyses were conducted to fine-map associated loci, identify relevant genes and pathways, and assess the genetic overlap between ACEi-AE and other traits. Finally, an exploratory cross-ancestry analysis was performed to assess shared genetic factors in European and African-American patients with ACEi-AE.

RESULTS

Three genome-wide significant risk loci were identified. One of these, located on chromosome 20q11.22, has not been implicated previously in ACEi-AE. Integrative secondary analyses highlighted previously reported genes (BDKRB2 [bradykinin receptor B2] and F5 [coagulation factor 5]) as well as biologically plausible novel candidate genes (PROCR [protein C receptor] and EDEM2 [endoplasmic reticulum degradation enhancing alpha-mannosidase like protein 2]). Lead variants at the risk loci were found with similar effect sizes and directions in an African-American cohort.

CONCLUSIONS

The present results contributed to a deeper understanding of the pathophysiology of ACEi-AE by (1) providing further evidence for the involvement of bradykinin signaling and coagulation pathways and (2) suggesting, for the first time, the involvement of the fibrinolysis pathway in this adverse drug reaction. An exploratory cross-ancestry comparison implicated the relevance of the associated risk loci across diverse ancestries.

Hereditary or acquired? Comprehensive genetic testing assists in stratifying angioedema patients

Hereditary angioedema (HAE) poses diagnostic challenges due to its episodic, non-specific symptoms and overlapping conditions. This study focuses on the genetic basis of HAE, particularly focusing on unresolved cases and those with normal C1-inhibitor levels (nC1-INH HAE). This study reveals that conventional testing identified pathogenic variants in only 10 patients (n = 32), emphasizing the necessity for an integrative approach using genome, exome, and transcriptome sequencing. Despite extensive genetic analyses, the diagnostic yield for nC1-INH HAE remains low in our study, the pathogenic variant for nC1-INH HAE was identified in only 1 patient (n = 21). Investigation into candidate genes yielded no pathogenic variants, prompting a re-evaluation of patients' diagnoses. This study advocates for a nuanced approach to genetic testing, recognizing its limitations and emphasizing the need for continuous clinical assessment. The complex genetic landscape of nC1-INH HAE necessitates further research for a more comprehensive understanding. In conclusion, this study contributes valuable insights into the genetic intricacies of HAE, highlighting the challenges in diagnosis and the evolving nature of the disease. The findings underscore the importance of advanced sequencing techniques and an integrated diagnostic strategy in unravelling the complexities of HAE, particularly in nС1-INH HAE cases.

A mechanism for hereditary angioedema caused by a methionine-379-to-lysine substitution in kininogens

ABSTRACT

Hereditary angioedema (HAE) is associated with episodic kinin-induced swelling of the skin and mucosal membranes. Most patients with HAE have low plasma C1-inhibitor activity, leading to increased generation of the protease plasma kallikrein (PKa) and excessive release of the nanopeptide bradykinin from high-molecular-weight kininogen (HK). However, disease-causing mutations in at least 10% of patients with HAE appear to involve genes for proteins other than C1-inhibitor. A point mutation in the Kng1 gene encoding HK and low-molecular weight kininogen (LK) was identified recently in a family with HAE. The mutation changes a methionine (Met379) to lysine (Lys379) in both proteins. Met379 is adjacent to the Lys380-Arg381 cleavage site at the N-terminus of the bradykinin peptide. Recombinant wild-type (Met379) and variant (Lys379) versions of HK and LK were expressed in HEK293 cells. PKa-catalyzed kinin release from HK and LK was not affected by the Lys379 substitutions. However, kinin release from HK-Lys379 and LK-Lys379 catalyzed by the fibrinolytic protease plasmin was substantially greater than from wild-type HK-Met379 and LK-Met379. Increased kinin release was evident when fibrinolysis was induced in plasma containing HK-Lys379 or LK-Lys379 compared with plasma containing wild-type HK or LK. Mass spectrometry revealed that the kinin released from wild-type and variant kininogens by PKa is bradykinin. Plasmin also released bradykinin from wild-type kininogens but cleaved HK-Lys379 and LK-Lys379 after Lys379 rather than Lys380, releasing the decapeptide Lys-bradykinin (kallidin). The Met379Lys substitutions make HK and LK better plasmin substrates, reinforcing the relationship between fibrinolysis and kinin generation.

The US Hereditary Angioedema Association Scientific Registry: hereditary angioedema demographics, disease severity, and comorbidities

BACKGROUND

Hereditary angioedema (HAE) and idiopathic nonhistaminergic angioedema (INHA) are ultra-rare diseases whose natural histories and comorbidities are incompletely understood.

OBJECTIVE

To develop a national patient-centric registry to address these deficiencies in our knowledge and improve our ability to assess the real-world impact of therapeutic interventions.

METHODS

Data from members of the US HAE Association were collected into an online registry between 2009 and April 7, 2021. Cohorts were categorized by reported physician diagnosis. Patient reported data were collected using a series of questionnaires. Demographic, natural history, and family history outcomes of the HAE due to C1 inhibitor deficiency (HAE-C1INH) participants were compared with those of the combined HAE with normal C1 inhibitor (HAE-nl-C1INH) plus INHA group. The prevalence of comorbid conditions in the HAE-C1INH group was compared with the general US population.

RESULTS

A total of 485 HAE-C1INH, 26 HAE-nl-C1INH, and 70 INHA participants were included in the analysis. Delay to diagnosis was shorter in HAE-C1INH (5 vs 11 years), but both had decreasing delays over time. Differences in attack frequency and location were found between the groups. Morbidity surrogates including emergency department visits, hospitalizations, unnecessary abdominal surgeries, and intubations were strikingly high as was mortality with 36.9% of HAE-C1INH and 15.4% of HAE-nl-C1INH participants reporting family members who died from a HAE attack. Females with HAE-C1INH had a significant increase in the prevalence of depression, sleep disorders, kidney disease, anemia, and hepatitis. Cardiovascular comorbidities were significantly reduced in the HAE-C1INH group.

CONCLUSION

The US HAEA Scientific Registry provides a mechanism to enhance our knowledge of HAE and INHA.

Patient-physician interactions in hereditary angioedema-Key learnings from the coronavirus disease 2019 pandemic

BACKGROUND

The coronavirus disease pandemic and its containing measures have caused concerns for patients with hereditary angioedema (HAE) and their treating physicians. Both faced challenges surrounding interaction, and communication had to adapt to facilitate appropriate management. Specifically, the pandemic resulted in reduced in-person contact in clinics. Where possible, telemedicine appointments were offered and treatment outside the hospital setting was encouraged. BODY: The pandemic markedly affected patient-physician communication, which is essential to maintain partnerships and optimize care. Although patients with HAE are often experts in their condition, guidance by their physicians is essential, especially with the recent shift toward patient-centered management for rare diseases and shared decision-making (SDM). SDM enables patients to take control of their disease and allows the risks and benefits of treatment to be discussed with their physicians. This review explores perspectives from patients and physicians in the HAE clinical setting, particularly regarding their experiences with communication throughout the pandemic. We discuss the importance of SDM in rare diseases such as HAE, factors that impact effective communication, and potential solutions.

CONCLUSION

Since patient-centered care and SDM have particular relevance in rare diseases in general, we believe our findings could be transferrable and applicable in the management of other rare diseases.

Angioedema With Normal Complement Studies: What Do We Know?

Angioedema is generally readily recognizable clinically and is characterized by localized nonpitting edema involving subcutaneous, submucosal, or deep dermal tissue caused by increased vascular permeability and extravasation of intravascular fluid. It can occur via a variety of mechanisms. A number of clinical conditions (masqueraders) are occasionally mistaken for angioedema. Clinical classification of the various angioedema forms begins with noting the presence or absence of concurrent urticaria or wheals. Pathogenesis can be considered through two broad categories: mast cell-mediated with release of vasoactive mediators causing angioedema usually associated with urticaria or in the context of an anaphylactic reaction; and bradykinin (BK)-driven, in which increased vascular permeability is mediated by BK. BK-mediated angioedema does not occur with urticaria, nor does it respond to antiallergic medications. The various forms of hereditary angioedema are included in this category, requiring specific tests of C4 and C1 inhibitor level and function to confirm the diagnosis. Angiotensin converting enzyme inhibitors, which impair the degradation of BK, account for up to a third of all patients with angioedema presenting to the emergency department. Finally, angioedema may occur by yet unknown mechanisms; under this circumstance, it is difficult to manage.

Genetic Variants Leading to Urticaria and Angioedema and Associated Biomarkers

Advances in next generation sequencing technologies, as well as their expanded accessibility and clinical use over the past 2 decades, have led to an exponential increase in the number of identified single gene disorders. Among these are primary atopic disorders-inborn errors of immunity resulting in severe allergic phenotypes as a primary presenting feature. Two cardinal aspects of type I immediate hypersensitivity allergic reactions are hives and angioedema. Mast cells (MCs) are frequent primary drivers of these symptoms, but other cells have also been implicated. Even where MC degranulation is believed to be the cause, mediator-induced symptoms may greatly vary among individuals. Angioedema-particularly in the absence of hives-may also be caused by hereditary angioedema conditions resulting from aberrant regulation of contact system activation and excessive bradykinin generation or impairment of vascular integrity. In these patients, swelling can affect unpredictable locations and fail to respond to MC-directed therapies. Genetic variants have helped delineate key pathways in the etiology of urticaria and nonatopic angioedema and led to the development of targeted therapies. Herein, we describe the currently known inherited and acquired genetic causes for these conditions, highlight specific features in their clinical presentations, and discuss the benefits and limitations of biomarkers that can help distinguish them.

Factor XII Structure-Function Relationships

Factor XII (FXII), the zymogen of the protease FXIIa, contributes to pathologic processes such as bradykinin-dependent angioedema and thrombosis through its capacity to convert the homologs prekallikrein and factor XI to the proteases plasma kallikrein and factor XIa. FXII activation and FXIIa activity are enhanced when the protein binds to a surface. Here, we review recent work on the structure and enzymology of FXII with an emphasis on how they relate to pathology. FXII is a homolog of pro-hepatocyte growth factor activator (pro-HGFA). We prepared a panel of FXII molecules in which individual domains were replaced with corresponding pro-HGFA domains and tested them in FXII activation and activity assays. When in fluid phase (not surface bound), FXII and prekallikrein undergo reciprocal activation. The FXII heavy chain restricts reciprocal activation, setting limits on the rate of this process. Pro-HGFA replacements for the FXII fibronectin type 2 or kringle domains markedly accelerate reciprocal activation, indicating disruption of the normal regulatory function of the heavy chain. Surface binding also enhances FXII activation and activity. This effect is lost if the FXII first epidermal growth factor (EGF1) domain is replaced with pro-HGFA EGF1. These results suggest that FXII circulates in blood in a "closed" form that is resistant to activation. Intramolecular interactions involving the fibronectin type 2 and kringle domains maintain the closed form. FXII binding to a surface through the EGF1 domain disrupts these interactions, resulting in an open conformation that facilitates FXII activation. These observations have implications for understanding FXII contributions to diseases such as hereditary angioedema and surface-triggered thrombosis, and for developing treatments for thrombo-inflammatory disorders.

Mechanisms involved in hereditary angioedema with normal C1-inhibitor activity

Patients with the inherited disorder hereditary angioedema (HAE) suffer from episodes of soft tissue swelling due to excessive bradykinin production. In most cases, dysregulation of the plasma kallikrein-kinin system due to deficiency of plasma C1 inhibitor is the underlying cause. However, at least 10% of HAE patients have normal plasma C1 inhibitor activity levels, indicating their syndrome is the result of other causes. Two mutations in plasma protease zymogens that appear causative for HAE with normal C1 inhibitor activity have been identified in multiple families. Both appear to alter protease activity in a gain-of-function manner. Lysine or arginine substitutions for threonine 309 in factor XII introduces a new protease cleavage site that results in formation of a truncated factor XII protein (Δ-factor XII) that accelerates kallikrein-kinin system activity. A glutamic acid substitution for lysine 311 in the fibrinolytic protein plasminogen creates a consensus binding site for lysine/arginine side chains. The plasmin form of the variant plasminogen cleaves plasma kininogens to release bradykinin directly, bypassing the kallikrein-kinin system. Here we review work on the mechanisms of action of the FXII-Lys/Arg309 and Plasminogen-Glu311 variants, and discuss the clinical implications of these mechanisms.

Biochemistry, molecular genetics, and clinical aspects of hereditary angioedema with and without C1 inhibitor deficiency

Hereditary angioedema (HAE) is a rare disorder characterized by cutaneous and submucosal swelling caused mostly by excessive local bradykinin production. Bradykinin is a vasoactive peptide generated by the limited proteolysis of high molecular weight kininogen (HMWK) by plasma kallikrein via the contact activation system. The contact activation system occurs not only in solution but also on the cell surface. Factor XII (FXII), prekallikrein, and HMWK are assembled on the endothelial cell surface via several proteins, including a trimer of a receptor for globular C1q domain in a Zn²⁺-dependent manner, and the reciprocal activation on the cell surface is believed to be physiologically important in vivo. Thus, the contact activation system leads to the activation of coagulation, complement, inflammation, and fibrinolysis. C1-inhibitor (C1-INH) is a plasma protease inhibitor that is a member of the serpin family. It mainly inhibits activated FXII (FXIIa), plasma kallikrein, and C1s. C1-INH hereditary deficiency induces HAE (HAE-C1-INH) due to excessive bradykinin production via the incomplete inhibition of plasma kallikrein and FXIIa through the low C1-INH level. HAE is also observed in patients with normal C1-INH (HAEnCI) who carry pathogenic variants in genes of factor XII, plasminogen, angiopoietin 1, kininogen, myoferlin, and heparan sulfate 3-O-sulfotransferase 6, which are associated with bradykinin production and/or vascular permeability. HAE-causing pathways triggered by pathogenic variants in patients with HAE-C1-INH and HAEnCI are reviewed and discussed.

The role of vasoactive peptides in skin homeostasis-focus on adiponectin and the kallikrein-kinin system

Vasoactive peptides often serve a multitude of functions aside from their direct effects on vasodynamics. This article will review the existing literature on two vasoactive peptides and their involvement in skin homeostasis: adiponectin and-as the main representative of the kallikrein-kinin system-bradykinin. Adiponectin is the most abundantly expressed adipokine in the human organism, where it is mainly localized in fat depots including subcutaneous adipose tissue, from where adiponectin can exert paracrine effects. The involvement of adiponectin in skin homeostasis is supported by a number of studies reporting the effects of adiponectin in isolated human keratinocytes, sebocytes, fibroblasts, melanocytes, and immune cells. Regarding skin pathology, the potential involvement of adiponectin in psoriasis, atopic dermatitis, scleroderma, keloid, and melanogenesis is discussed in this article. The kallikrein-kinin system is composed of a variety of enzymes and peptides, most of which have been identified to be expressed in the skin. This also includes the expression of bradykinin receptors on most skin cells. Bradykinin is one of the very few hormones that is targeted by treatment in routine clinical use in dermatology-in this case for the treatment of hereditary angioedema. The potential involvement of bradykinin in wound healing, psoriasis, and melanoma is further discussed in this article. This review concludes with a call for additional preclinical and clinical studies to further explore the therapeutic potential of adiponectin supplementation (for psoriasis, atopic dermatitis, wound healing, scleroderma, and keloid) or pharmacological interference with the kallikrein-kinin system (for wound healing, psoriasis, and melanoma).

Hereditary Angioedema During Pregnancy: Considerations in Management

In recent years, hereditary angioedema (HAE) management has substantially advanced but also become more complex with additional therapeutic options. Pregnancy significantly influences the clinical symptoms of HAE in many women because of estrogen effects or other physiologic factors, and also introduces important safety concerns related to HAE medications. Management of HAE during pregnancy requires clinicians to be familiar with the potential clinical course, triggers, and recommended treatment strategies to provide guidance and optimal medical management to women and families affected by the condition. This review provides an overview of data, considerations, and recommendations related to HAE and pregnancy.

Interventions for the long-term prevention of hereditary angioedema attacks

BACKGROUND

Hereditary angioedema (HAE) is a serious and potentially life-threatening condition that causes acute attacks of swelling, pain and reduced quality of life. People with Type I HAE (approximately 80% of all HAE cases) have insufficient amounts of C1 esterase inhibitor (C1-INH) protein; people with Type II HAE (approximately 20% of all cases) may have normal C1-INH concentrations, but, due to genetic mutations, these do not function properly. A few people, predominantly females, experience HAE despite having normal C1-INH levels and C1-INH function (rare Type III HAE). Several new drugs have been developed to treat acute attacks and prevent recurrence of attacks. There is currently no systematic review and meta-analysis that included all preventive medications for HAE.

OBJECTIVES

To assess the benefits and harms of interventions for the long-term prevention of HAE attacks in people with Type I, Type II or Type III HAE.

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest search date was 3 August 2021.

SELECTION CRITERIA

We included randomised controlled trials in children or adults with HAE that used medications to prevent HAE attacks. The comparators could be placebo or active comparator, or both; approved and experimental drug trials were eligible for inclusion. There were no restrictions on dose, frequency or intensity of treatment. The minimum length of four weeks of treatment was required for inclusion; this criterion excluded the acute treatment of HAE attacks.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were 1. HAE attacks (number of attacks per person, per population) and change in number of HAE attacks; 2. mortality and 3. serious adverse events (e.g. hepatic dysfunction, hepatic toxicity and deleterious changes in blood tests). Our secondary outcomes were 4. quality of life; 5. severity of breakthrough attacks; 6. disability and 7. adverse events (e.g. weight gain, mild psychological changes and body hair). We used GRADE to assess certainty of evidence for each outcome.

MAIN RESULTS

We identified 15 studies (912 participants) that met the inclusion criteria. The studies included people with Type I and II HAE. The studies investigated avoralstat, berotralstat, subcutaneous C1-INH, plasma-derived C1-INH, nanofiltered C1-INH, recombinant human C1-INH, danazol, and lanadelumab for the prevention of HAE attacks. We did not find any studies on the use of tranexamic acid for prevention of HAE attacks. All drugs except avoralstat reduced the number of HAE attacks compared with placebo. For breakthrough attacks that occurred despite prophylactic treatment, intravenous and subcutaneous forms of C1-INH and lanadelumab reduced attack severity. It is not known whether other drugs have a similar effect, as the severity of breakthrough attacks in people taking drugs other than C1-INH and lanadelumab was not reported. For quality of life, avoralstat, berotralstat, C1-INH (all forms) and lanadelumab increased quality of life compared with placebo; there were no data for danazol. Four studies reported on changes in disability during treatment with C1-INH, berotralstat and lanadelumab; all three drugs decreased disability compared with placebo. Adverse events, including serious adverse events, did not occur at a rate higher than placebo. However, serious adverse event data and other adverse event data were not available for danazol, which prevented us from drawing conclusions about the absolute or relative safety of this drug. No deaths were reported in the included studies. The analysis was limited by the small number of studies, the small number of participants in each study and the lack of data on older drugs, therefore the certainty of the evidence is low. Given the rarity of HAE, it is not surprising that drugs were rarely directly compared, which does not allow conclusions on the comparative efficacy of the various drugs for people with HAE. Finally, we did not identify any studies that included people with Type III HAE. Therefore, we cannot draw any conclusions about the efficacy or safety of any drug in people with this form of HAE.

AUTHORS' CONCLUSIONS

The available data suggest that berotralstat, C1-INH (subcutaneous, plasma-derived, nanofiltered and recombinant), danazol and lanadelumab are effective in lowering the risk or incidence (or both) of HAE attacks. In addition, C1-INH and lanadelumab decrease the severity of breakthrough attacks (data for other drugs were not available). Avoralstat, berotralstat, C1-INH (all forms) and lanadelumab increase quality of life and do not increase the risk of adverse events, including serious adverse events. It is possible that danazol, subcutaneous C1-INH and recombinant human C1-INH are more effective than berotralstat and lanadelumab in reducing the risk of breakthrough attacks, but the small number of studies and the small size of the studies means that the certainty of the evidence is low. This and the lack of head-to-head trials prevented us from drawing firm conclusions on the relative efficacy of the drugs.

Complement Genetics for the Practicing Allergist Immunologist: Focus on Complement Deficiencies

Complement deficiencies have been considered to be rare for many decades, but this assumption is changing year by year. Recognition of these conditions significantly increases thanks to the availability of different testing approaches and due to clinical awareness. Furthermore, sequencing technologies (including Sanger sequencing, targeted gene panels, and whole exome/genome sequencing) may facilitate the identification of the underlying disease-causing genetic background. On the other hand, functional characterization of the identified possibly pathogenic variations and performing family studies, as illustrated by some of our cases, remain similarly important to establish a precise clinical diagnosis facilitating the most appropriate management. Here, we present 4 illustrative cases with complement deficiencies of diverse etiologies and also provide an educative, step-by-step description on how to identify the underlying cause of complement deficiency based on the results of complement laboratory testing.

Differential Diagnosis of Urticarial Lesions

Urticaria is a mast cell-dependent disease, characterized by the presence of wheals, angioedema, or both in the absence of systemic symptoms. It is a common disease worldwide, with an important health burden especially in chronic situations, that last more than 6 weeks. Although urticaria is usually a straightforward diagnosis, some diseases presenting with urticarial lesions must be excluded, particularly urticarial vasculitis and auto-inflammatory syndromes. In these settings additional atypical features are often present (long-lasting lesions, bruising, fever, malaise, arthralgia), allowing the clinician to suspect a diagnosis other than urticaria. The authors propose an approach based on these atypical features, the presence or absence of systemic symptoms and on skin histopathology as well as some blood parameters.

A mechanism for hereditary angioedema caused by a lysine 311-to-glutamic acid substitution in plasminogen

Patients with hereditary angioedema (HAE) experience episodes of bradykinin (BK)-induced swelling of skin and mucosal membranes. The most common cause is reduced plasma activity of C1 inhibitor, the main regulator of the proteases plasma kallikrein (PKa) and factor XIIa (FXIIa). Recently, patients with HAE were described with a Lys311 to glutamic acid substitution in plasminogen (Plg), the zymogen of the protease plasmin (Plm). Adding tissue plasminogen activator to plasma containing Plg-Glu311 vs plasma containing wild-type Plg (Plg-Lys311) results in greater BK generation. Similar results were obtained in plasma lacking prekallikrein or FXII (the zymogens of PKa and FXIIa) and in normal plasma treated with a PKa inhibitor, indicating Plg-Glu311 induces BK generation independently of PKa and FXIIa. Plm-Glu311 cleaves high and low molecular weight kininogens (HK and LK, respectively), releasing BK more efficiently than Plm-Lys311. Based on the plasma concentrations of HK and LK, the latter may be the source of most of the BK generated by Plm-Glu311. The lysine analog ε-aminocaproic acid blocks Plm-catalyzed BK generation. The Glu311 substitution introduces a lysine-binding site into the Plg kringle 3 domain, perhaps altering binding to kininogens. Plg residue 311 is glutamic acid in most mammals. Glu311 in patients with HAE, therefore, represents reversion to the ancestral condition. Substantial BK generation occurs during Plm-Glu311 cleavage of human HK, but not mouse HK. Furthermore, mouse Plm, which has Glu311, did not liberate BK from human kininogens more rapidly than human Plg-Lys311. This indicates Glu311 is pathogenic in the context of human Plm when human kininogens are the substrates.

Specific Targeting of Plasma Kallikrein for Treatment of Hereditary Angioedema: A Revolutionary Decade

Hereditary angioedema (HAE) is a rare, chronic, genetic disease that presents with nonpruritic angioedema of the face, extremities, airway (can be life-threatening), genitourinary system, and abdomen. These symptoms can significantly impair daily activities. Hereditary angioedema is classified into HAE owing to a deficiency of functional C1INH (HAE-C1INH) or HAE with normal C1INH (HAE-nl-C1INH). Both type I and II HAE-C1INH result from inherited or spontaneous mutations in the SERPING1 gene, which encodes for C1INH. These mutations result in C1INH dysfunction, leading to uncontrolled plasma kallikrein activity with excessive bradykinin production. Bradykinin receptor activation leads to vasodilation, increased vascular permeability, and smooth muscle contractions, resulting in submucosal angioedema through fluid extravasation. Hereditary angioedema nl-C1INH is caused by either a known or unknown genetic mutation. The underlying mechanism of HAE-nl-C1INH is less well understood but is thought to be related to bradykinin signaling. Plasma kallikrein inhibitors have been developed to inhibit the kallikrein-kinin pathway to prevent (prophylactic) and treat on-demand (acute) HAE attacks. Several of these medications are delivered through subcutaneous or intravenous injection, although new and emerging therapies include oral formulations. This article provides a historical review and describes the evolving landscape of available kallikrein inhibitors to treat HAE-C1INH.

Pregnancy in Patients With Hereditary Angioedema and Normal C1 Inhibitor

Background

HAE with normal C1 inhibitor (HAE-nC1-INH) has been identified as a bradykinin mediated angioedema. Estrogens are one of the main trigger factors. Pregnancy in HAE with C1 inhibitor deficiency showed variable course, however, few reports are available for HAE-nC1-INH. We evaluated the course of pregnancies in women diagnosed with HAE-nC1-INH.

Methods

Women with diagnosis of HAE-nC1-INH according to the following criteria: clinical manifestations similar to HAE-C1-INH, normal biochemical evaluation and family history were included. A questionnaire about pregnancies was applied after consent. Genetic evaluation for known mutations was performed in all patients.

Results

A total of 45 pregnancies occurring in 26 HAE-nC1-INH patients were evaluated (7/26 patients with F12 variant). Spontaneous abortion was reported in 8/45 (17.8%) pregnancies. Onset of attacks started before the pregnancy in 18/26 patients; during the pregnancy in 2/26; and after the pregnancy in 6/26. HAE attacks occurred in 24/37 pregnancies (64,7%): during the 1st trimester in 41.7%; 2nd trimester in 12.5%; 3rd trimester in 20.8%; 1st and 3rd trimesters in 4.2% and during the whole pregnancy in 20.8%. Among 15/18 patients who had attacks before pregnancy, symptoms persisted with worsening in 9/15; improvement in 4/15; no change in 1/15, and no response in 1/15.

Conclusions

The occurrence of abortion in HAE-nC1-INH was similar to the expected for not affected women. The 1st trimester of the pregnancy was more symptomatic for HAE-nC1-INH women. Considering the strong relevance of estrogens in HAE-nC1-INH, pregnancy could worsen the course of disease.

A Model for Surface-Dependent Factor XII Activation: The Roles of Factor XII Heavy Chain Domains

The FXII EGF1 domain promotes surface binding, FXII activation on surfaces, and FXIIa activation of prekallikrein on surfaces.

The FXII FN2 and KNG domains are part of a mechanism that restricts FXII activation in the absence of a surface.

Factor XII (FXII) is the zymogen of a plasma protease (FXIIa) that contributes to bradykinin generation by converting prekallikrein to the protease plasma kallikrein (PKa). FXII conversion to FXIIa by autocatalysis or PKa-mediated cleavage is enhanced when the protein binds to negatively charged surfaces such as polymeric orthophosphate. FXII is composed of noncatalytic (heavy chain) and catalytic (light chain) regions. The heavy chain promotes FXII surface-binding and surface-dependent activation but restricts activation when FXII is not surface bound. From the N terminus, the heavy chain contains fibronectin type 2 (FN2), epidermal growth factor-1 (EGF1), fibronectin type 1 (FN1), EGF2, and kringle (KNG) domains and a proline-rich region. It shares this organization with its homolog, pro–hepatocyte growth factor activator (Pro-HGFA). To study the importance of heavy chain domains in FXII function, we prepared FXII with replacements of each domain with corresponding Pro-HGFA domains and tested them in activation and activity assays. EGF1 is required for surface-dependent FXII autoactivation and surface-dependent prekallikrein activation by FXIIa. KNG and FN2 are important for limiting FXII activation in the absence of a surface by a process that may require interactions between a lysine/arginine binding site on KNG and basic residues elsewhere on FXII. This interaction is disrupted by the lysine analog ε-aminocaproic acid. A model is proposed in which an ε-aminocaproic acid–sensitive interaction between the KNG and FN2 domains maintains FXII in a conformation that restricts activation. Upon binding to a surface through EGF1, the KNG/FN2-dependent mechanism is inactivated, exposing the FXII activation cleavage site.

The prevalence of hereditary angioedema in a Chinese cohort with decreased complement 4 levels

Objective

Hereditary angioedema (HAE) is a rare, life-threatening autosomal dominant disorder. We aimed to investigate the prevalence of HAE in a Chinese population with a decreased Complement 4 (C4) level.

Methods

All the patients present in Tongji Hospital with C4 below lower normal range were included from January 2019 to June 2020. The individual data were extracted from the database and categorized by diagnosis. Patients suspected of HAE were further evaluated by C1 inhibitor level and function test to confirm the HAE diagnosis.

Results

A total of 8226 patients were enrolled in our study, among whom 18 had symptoms similar to HAE and received C1 inhibitor level and function tests. Two (1 male and 1 female) of the 18 patients were identified as HAE patients. This means the prevalence of HAE was 2.43/10 000 among the C4-decreased population and 10.1/10 000 in the C4-decreased population with etiology undetermined. The 2 HAE patients had experienced skin and oropharynx edema attack and received tracheotomy. The female patient had a family history. Laboratory tests showed significant decrease of C4 and C1 inhibitor levels in the 2 patients, both of whom were diagnosed as type 1 HAE.

Conclusion

The prevalence of HAE is low in C4-decreased patients. In a large cohort, C4 level can serve as a practical indicator to screen the HAE patients, but further testing of C1 inhibitor activity and levels is needed to confirm the diagnosis of HAE.

Clinical features of hereditary angioedema and warning signs (H4AE) for its identification

OBJECTIVES

The study describes a case series of hereditary angioedema with C1 Inhibitor Deficiency (C1INH-HAE) in order to corroborate six clinical warning signs "HAAAAE (H4AE)" to enable early identification of this disease.

METHODS

The authors analyzed the C1INH-HAE cohort to analyze the clinical aspects of the present study's patients and corroborate the six clinical warning signs of the Hereditary Angioedema Brazilian Guidelines. Data regarding demographics, the onset of disease, time to diagnosis, frequency of attacks per year, organs involved, triggers, crisis duration and their outcomes, and disease treatment were collected. Then the authors developed an acronym, H4AE, to help healthcare professionals remember the warning signs.

RESULTS

The authors included 98 patients in the study, with a mean age of 38.1 years, 67.3% being female, and 75.3% with a family history of HAE. HAE diagnosis was delayed, on average, 13.7 years after its initial manifestation. Exploratory laparotomy was reported by 26.9%, and orotracheal intubation by 21.3% of the present study's patients; 61.3% and 30.3% of them were admitted at least once in the hospital and in the intensive care unit, respectively. The authors constructed an acronym "H4AE" with the six warning signs of HAE: Hereditary, recurrent Angioedema, Abdominal pain, Absence of urticaria, Absence of response to antihistamines, Estrogen association.

CONCLUSION

C1INH-HAE is still underdiagnosed and associated with high morbidity. The study showed clinical features of this disease, corroborating the warning signs, which may be useful in raising awareness and improving the diagnosis of C1INH-HAE. The authors suggest the acronym "H4AE" to remind the warning signs.

Hereditary Angioedema: Diagnostic Algorithm and Current Treatment Concepts

Hereditary angioedema (HAE) is an uncommon disorder with a global prevalence of approximately 1 in 10,000 to 1 in 50,000 population. This disease is grossly underrecognized in India because of lack of awareness and/or lack of diagnostic facilities. Clinical manifestations include swelling over face, eyes, lips, hands, feet, and genitals, abdominal pain, and life-threatening laryngeal edema. HAE should be suspected in all patients who present with angioedema without wheals and who do not respond to antihistamines and/or steroids. C1 levels, C1-INH levels, and C1-INH function should be checked in all patients suspected to have HAE. C1q levels should be assessed in patients with suspected autoimmune-mediated acquired angioedema. Management of HAE constitutes the treatment of acute attack and short-term and long-term prophylaxis. Because of lack of all first-line recommended medications, the management of HAE in India is a challenging task. Patients are managed using fresh frozen plasma (acute treatment), tranexamic acid, and attenuated androgens (prophylaxis). Even though attenuated androgens have been shown to be effective in the prevention of attacks of HAE, the side effect profile especially in children and in females is a serious concern. Hence, the treatment needs to be individualized considering the risk-benefit ratio of long-term prophylaxis. In this review, we provide an overview of diagnostic strategy for patients with HAE and the current treatment concepts with emphasis on currently available treatment options in resource-constrained settings.

Hereditary Angioedema: A Gynecology and Obstetrics Perspective

Hereditary angioedema is an autosomal dominant genetic disease that causes tissue edema mediated by bradykinin. The angioedema attacks have several triggers including stress, trauma, infection, and increased estrogens levels. This explains the greater incidence and clinical severity in women, which are usually asymptomatic until puberty, when the attacks begin to occur. It may involve multiple locations on the body, leading to complications, such as surgical intervention prompt by severe acute abdominal pain, and laryngeal edema that can culminate in death from asphyxia. This is of particular concern as this angioedema does not respond to life-saving medications commonly used in its treatment, namely, high doses of second-generation antihistamines, corticosteroids, and epinephrine. Hereditary angioedema attacks are treated with specific medication that includes icatibant, ecallantide, and C1 inhibitor, the latter being also used in short-term and long-term prophylaxis. There are other pharmacological strategies for long-term prophylaxis like lanadelumab, danazol, stanozolol, aminocaproic acid, and tranexamic acid. During pregnancy and lactation, the preferred treatment and prophylaxis is C1 inhibitor.

We report a case of hereditary angioedema describing its chronological evolution over a period of a woman's life, and highlighting some of the specificities of this pathology that intersect with the specialty of Obstetrics and Gynecology. Our aim is to draw attention to these particularities, namely the triggering factors of crisis, the need for high suspicion of the diagnosis, and the treatment and prophylaxis options for pregnant and non-pregnant women that can make the difference between life and death. To achieve a favorable outcome, the multidisciplinary teamwork between the specialties of Immunoallergology and Obstetrics and Gynecology was crucial.

First Census of Patients with Hereditary Angioedema in the Canary Islands

Hereditary angioedema (HAE) is a rare genetic condition whose main symptoms are recurrent swelling in the skin, mucosa, and internal organs. Recent studies suggested that the regulation of the inflammatory response and the complement cascade are two of the pathways significantly enriched in the Canary Islands, Spain. Here, we describe the first HAE patient series in this region. Forty-one patients (33 F, 8 M) and nine healthy relatives belonging to twenty-nine families were recruited for this study, obtaining their clinical and demographic features using a data collection form, as well as blood samples for biochemical analysis. The mean age of patients was 36.8 years (ranging from 4 to 72 years). Positive family history of HAE was reported in 13 patients (32.5%), and a mean diagnosis delay of 7.9 (±12.5) years was estimated, ranging from months to 50 years. Cutaneous edema was the most common symptom (53.6%), while airway symptoms was present in 11 patients. Prophylactic treatment was indicated for 23 patients, while 14 also require on-demand rescue treatment. We estimate a minimum prevalence of 1.25:100,000 for HAE due to C1-INH deficiency or dysfunction in the Canary Islands, which is higher than the estimates for mainland Spanish populations. HAE continues to be a disease poorly recognized by health care professionals due to its confusing symptoms, leading to longer diagnosis delay. Altogether, the evidence reinforces the need for a rapid and accurate diagnosis and precision medicine-based studies to improve the patient's quality of life.

Expanding Horizons in Complement Analysis and Quality Control

Complement not only plays a key role in host microbial defense but also modulates the adaptive immune response through modification of T- and B-cell reactivity. Moreover, a normally functioning complement system participates in hematopoiesis, reproduction, lipid metabolism, and tissue regeneration. Because of its powerful inflammatory potential, multiple regulatory proteins are needed to prevent potential tissue damage. In clinical practice, dysregulation and overactivation of the complement system are major causes of a variety of inflammatory and autoimmune diseases ranging from nephropathies, age-related macular degeneration (AMD), and systemic lupus erythematosus (SLE) to graft rejection, sepsis, and multi-organ failure. The clinical importance is reflected by the recent development of multiple drugs targeting complement with a broad spectrum of indications. The recognition of the role of complement in diverse diseases and the advent of complement therapeutics has increased the number of laboratories and suppliers entering the field. This has highlighted the need for reliable complement testing. The relatively rapid expansion in complement testing has presented challenges for a previously niche field. This is exemplified by the issue of cross-reactivity of complement-directed antibodies and by the challenges of the poor stability of many of the complement analytes. The complex nature of complement testing and increasing clinical demand has been met in the last decade by efforts to improve the standardization among laboratories. Initiated by the IUIS/ICS Committee for the Standardization and Quality Assessment in Complement Measurements 14 rounds of external quality assessment since 2010 resulted in improvements in the consistency of testing across participating institutions, while extending the global reach of the efforts to more than 200 laboratories in 30 countries. Worldwide trends of assay availability, usage, and analytical performance are summarized based on the past years’ experiences. Progress in complement analysis has been facilitated by the quality assessment and standardization efforts that now allow complement testing to provide a comprehensive insight into deficiencies and the activation state of the system. This in turn enables clinicians to better define disease severity, evolution, and response to therapy.

Hormonal Effects on Urticaria and Angioedema Conditions

Women appear to be more frequently affected with urticaria and angioedema. Sex hormones are believed to have an important mechanistic role in regulating pathways involved in these conditions. This effect is likely nonspecific for chronic spontaneous urticaria (CSU) or many forms of angioedema (AE), because many other chronic diseases such as asthma are also affected by sex hormones. The role of sex hormones has been better elucidated for hereditary AE, because they have been shown to have multiple effects including upregulation of FXII, an important activator of the kallikrein pathway. However, their role in the underlying pathogenesis for CSU is less clear. Autoimmunity is clearly linked to CSU, which is more common in women. This suggests that sex hormones could act as adjuvants in activating or upregulating autoimmune pathways. The purpose of this review is to discuss in detail the role of sex hormones in CSU and AE and how a better understanding of the impact hormones has on these conditions might lead to new treatment advancements with better clinical outcomes.