Hereditary angioedema: an update on causes, manifestations and treatment.

Hereditary angioedema is a rare genetic disorder caused by deficiency of C1 esterase inhibitor (C1-INH) and characterized by recurrent episodes of severe swelling that affect the limbs, face, intestinal tract and airway. Since laryngeal oedema can be life-threatening as a result of asphyxiation, correct diagnosis and management of hereditary angioedema is vital. Hereditary angioedema attacks are mediated by bradykinin, the production of which is regulated by C1-INH. Hereditary angioedema therapy relies on treatment of acute attacks, and short- and long-term prophylaxis. Acute treatment options include C1-INH concentrate, icatibant and ecallantide. Self-administration of treatment is recommended and is associated with increased quality of life of patients with hereditary angioedema. Advances in diagnosis and management have improved the outcomes and quality of life of patients with hereditary angioedema.

Cost-Effectiveness of Prophylactic Medications for the Treatment of Hereditary Angioedema Due to C1 Inhibitor Deficiency: A Real-World U.S. Perspective.

DISCLOSURES: No funding supported the writing of this commentary. The author reports personal fees from BioCryst, CSL Behring, Shire, and Pharming and grants from Ionis. He is chair of the US HAEA Medical Advisory Board and scientific advisor for HAE International.

Fixed-Dose Subcutaneous C1-Inhibitor Liquid for Prophylactic Treatment of C1-INH-HAE: SAHARA Randomized Study.

BACKGROUND: Hereditary angioedema (HAE) with C1 inhibitor deficiency (C1-INH) is characterized by swelling of subcutaneous and/or submucosal tissues. OBJECTIVE: To evaluate efficacy/safety of fixed-dose subcutaneous plasma-derived C1-INH (pdC1-INH) liquid for HAE attack prevention (NCT02584959). METHODS: Eligible patients were ≥12 years with ≥2 monthly attacks prescreening or pre-long-term prophylaxis. In a partial crossover design, 80% of patients were randomized to placebo or pdC1-INH liquid for 14 weeks and crossed over from active to placebo or vice versa for another 14 weeks. The remainder were randomized to pdC1-INH liquid for 28 weeks. The primary efficacy endpoint was normalized number of attacks (NNA) versus placebo. Key additional endpoints were the proportion of patients achieving NNA reduction ≥50%, attack severity, number of attack-free days, and safety. RESULTS: Seventy-five patients were randomized and 58 (77%) completed the study. Mean age 41 years; 88% HAE type I. Least-squares means of NNA were reduced from 3.9 with placebo to 1.6 with pdC1-INH (from day 1; P < .0001). Most patients had ≥50% NNA reduction with pdC1-INH (from day 1, 78%). A total of 8.8% of placebo-treated patients were attack-free and 5.3%, 22.8%, and 63.2% had mild, moderate, and severe attacks, respectively; 37.5% of pdC1-INH-treated patients were attack-free and 8.9%, 26.8%, and 26.8% had mild, moderate, and severe attacks, respectively. Treatment-emergent adverse event rates were similar between groups (52% vs 56% for pdC1-INH crossover vs placebo, respectively). CONCLUSIONS: Fixed-dose subcutaneous pdC1-INH liquid was superior to placebo in preventing HAE attacks and demonstrated a favorable safety profile.

Hereditary angioedema: the plasma contact system out of control.

The plasma contact system contributes to thrombosis in experimental models. Even though our standard blood coagulation tests are prolonged when plasma lacks contact factors, this enzyme system appears to have a minor (if any) role in hemostasis. In this review, we explore the clinical phenotype of C1 esterase inhibitor (C1-INH) deficiency. C1-INH is the key plasma inhibitor of the contact system enzymes, and its deficiency causes hereditary angioedema (HAE). This inflammatory disorder is characterized by recurrent aggressive attacks of tissue swelling that occur at unpredictable locations throughout the body. Bradykinin, which is considered to be a byproduct of the plasma contact system during in vitro coagulation, is the main disease mediator in HAE. Surprisingly, there is little evidence for thrombotic events in HAE patients, suggesting mechanistic uncoupling from the intrinsic pathway of coagulation. In addition, it is questionable whether a surface is responsible for contact system activation in HAE. In this review, we discuss the clinical phenotype, disease modifiers and diagnostic challenges of HAE. We subsequently describe the underlying biochemical mechanisms and contributing disease mediators. Furthermore, we review three types of HAE that are not caused by C1-INH inhibitor deficiency. Finally, we propose a central enzymatic axis that we hypothesize to be responsible for bradykinin production in health and disease.

An update on the diagnosis and management of hereditary angioedema with abnormal C1 inhibitor.

Hereditary angioedema (HAE) is a rare genetic disease caused by a deficiency in functional C1-esterase inhibitor characterized by recurrent episodes of angioedema in the absence of associated urticaria. Subcutaneous swellings are experienced by virtually all patients with HAE, and dermatologists are likely to encounter this manifestation, requiring that they be knowledgeable about diagnosis and treatment options. Diagnosis of HAE is often delayed because several of the symptoms can mimic other disease states. Delays in diagnosis can lead to increased inappropriate treatment and decreased patient quality of life. Once a proper diagnosis is made, treatment needs to be targeted to the individual patient and includes on-demand therapy and an option for short- and long-term prophylaxis. On-demand therapy is required for all patients who are diagnosed with HAE and effective options include plasma-derived and recombinant C1 inhibitors, kallikrein inhibitors, and bradykinin B2-receptor antagonists. Options available for prophylaxis include plasma-derived C1 inhibitors, attenuated androgens, and antifibrinolytic agents, although the latter 2 options are associated with significant adverse events. This article reviews the diagnosis and options for effective management of patients with HAE.

Clinical Pattern and Acute and Long-term Management of Hereditary Angioedema Due to C1-Esterase Inhibitor Deficiency.

BACKGROUND: Hereditary angioedema due to C1-esterase inhibitor deficiency (HAE-C1-INH) is a life-threatening disease. OBJECTIVES: To describe the clinical characteristics and management of patients with HAE-C1-INH during routine clinical practice. METHODS: An observational, retrospective study was performed in patients with HAE-C1-INH. Demographic, clinical, and analytical data were collected from 2 periods: period A (October 2009-September 2010) and period B (October 2007-September 2009). RESULTS: We studied 112 patients with HAE-C1-INH (57.1% females). Age at onset of symptoms was 14.4 years (lower in patients who had experienced attacks in the previous year). In period B (n=87), 62.1% of patients presented at least 1 edema attack (median, 3.5 attacks/patient/2 years), and 19.1% of attacks were treated. In period A (n=77), 58.4% of patients were on maintenance therapy. Stanozolol was the most widely used drug (48.9%), with a mean weekly dose of 6.7 mg. At least 1 attack was recorded in 72.7% of patients (median, 3.0 attacks/patient/year), and 31.5% of the attacks were treated. Treatment of acute attacks increased by 12.4%. CONCLUSION: Age at onset of symptoms is associated with clinical expression of disease. The higher age at onset of symptoms, the fewer number of attacks per patient and year, and the lower dose of attenuated androgens necessary to control the disease than in other series lead us to hypothesize that HAE-C1-INH could have a less severe expression in Spain. Acute attacks seem to be treated increasingly often.

Abdominal attacks and treatment in hereditary angioedema with C1-inhibitor deficiency.

BACKGROUND: Hereditary angioedema (HAE) is characterized by unpredictable attacks of debilitating subcutaneous and mucosal edema. Gastrointestinal attacks are painful, of sudden onset and often mistaken for acute abdomen leading to unnecessary surgery. The purpose of this study was to analyze symptom presentation of gastrointestinal angioedema in pediatric and adult HAE patients. METHODS: Information collected during the clinical development of ecallantide for treatment of acute HAE attacks included affected anatomic location, accompanying symptoms, medical history, and pain assessments. Efficacy endpoints included Treatment Outcome Score (TOS, maximum score = 100; minimally important difference = 30), a point-in-time measure of treatment response, and time to treatment response. RESULTS: Forty-nine percent of 521 HAE attacks only involved abdominal symptoms. The most commonly reported abdominal symptoms were distension (77%), cramping (73%) and nausea (67%). The most common pain descriptors were tender, tiring-exhausting, aching, cramping and sickening. White blood cell counts were elevated (>10 × 10(9)/L) in 23% of attacks (mean ± SD: 15.1 ± 11.27 × 10(9)/L). A high proportion of patients reported a history of abdominal surgery, including appendectomy (23%), cholecystectomy (16.4%), and hysterectomy (8.2%). Mean TOS at 4 hours post ecallantide was 77 ± 33 versus 29 ± 65 for placebo. Median time to significant symptom resolution was 165 minutes (95% CI 136, 167) for ecallantide versus >4 hours (95% CI 161, >4 hours) for placebo. Anaphylactic reactions occurred in 6 of the 149 treated patients. CONCLUSIONS: HAE should be considered in the differential diagnosis of patients with recurrent discrete episodes of severe, unexplained crampy abdominal pain associated with nausea. TRIALS REGISTRATION: The data used in the analysis were gathered across multiple clinical trials conducted during the clinical development program for ecallantide. All of the studies were conducted using Good Clinical Practices (GCP) and in accordance with the ethical principles that have their origins in the Declaration of Helsinki. Each site that participated in the clinical trials obtained the appropriate IRB or Ethics Committee approval prior to enrolling any patients. All patients provided written informed consent prior to undergoing any study-related procedures. Pediatric patients provided written assent and their parents or guardians gave written informed consent.The following trials have been registered at http://www.clinicaltrials.gov: EDEMA2 (identifier NCT01826916); EDEMA3 (identifier NCT00262080); EDEMA4 (identifier NCT00457015); and DX-88/19 (identifier NCT00456508).

Disease-modifying factors in hereditary angioedema: an RNA expression-based screening.

BACKGROUND: Hereditary Angioedema due to C1-Inhibitor deficiency (HAE types I and II) is a monogenic disease characterized by sudden, self-limited episodes of cutaneous and mucosal swelling due to local deregulation of vascular permeability. Despite its monogenic pattern of inheritance, HAE exhibits great clinical variability and low genotype/phenotype correlation among those affected, which ultimately hinders therapeutic approach and probably underlies yet unknown genetic and environmental factors. METHODS: We studied whole-genome RNA expression of PBMCs in three HAE type-I families (accounting for 40 individuals), 24 of which carry the same R472X mutation in the C1-Inhibitor gene and show large variability in terms of disease expression. Those included in this study were analyzed according to the presence of mutation and/or clinical symptoms. RESULTS: Instead of a single, common disease-associated expression pattern, we found different transcriptome signatures in two of the families studied. In one of them (referred to as DR family), symptoms correlate with the upregulation of 35 genes associated to the biological response to viral infections (including RSADs, OAS, MX and ISG pathway members) and immune response. In another pedigree (Q family), disease manifestation is linked to the upregulation of 43 genes with diverse functions, including transcription and protein folding. Moreover, symptoms-free members of the Q pedigree display relatively higher expression of 394 genes with a wide diversity of functions. CONCLUSION: We found no evidence for a common altered PBMC expression pattern linked to HAE symptoms in the three families analyzed. All the data considered, differential gene expression in PBMCs do not seem to play a significant role in the predisposition or protection against HAE in the basal -between crises- conditions analyzed. Although the RNA expression pattern associated to the response to viral infections observed in the DR family supports the idea of infectious diseases as a modifying factor for HAE severity, large-scale studies would be needed to statistically associate such expression pattern to the development of this rare disease.

Overview of hereditary angioedema caused by C1-inhibitor deficiency: assessment and clinical management.

Hereditary angioedema due to C1-inhibitor deficiency (HAE-C1-INH) is a rare, autosomal-dominant disease. HAE-C1-INH is characterized by recurrent attacks of marked, diffuse, nonpitting and nonpruritic skin swellings, painful abdominal attacks, and laryngeal edema. The extremities and the gastrointestinal tract are most commonly affected. Swelling of the upper respiratory mucosa poses the greatest risk because death from asphyxiation can result from laryngealedema. HAE-C1-INH attacks are variable, unpredictable, and may be induced by a variety of stimuli, including stress or physical trauma. Because the clinical presentation of HAE-C1-INH is similar to other types of angioedema, the condition may be a challenge to diagnose. Accurate identification of HAE-C1-INH is critical in order to avoid asphyxiation by laryngeal edema and to improve the burden of disease. Based on an understanding of the underlying pathophysiology of IHAE-C1-INH, drugs targeted specifically to the disease, such as C1-inhibitor therapy, bradykinin B2-receptor antagonists, and kallikrein-inhibitors, have become available for both treatment and prevention of angioedema attacks. This article reviews the clinical features, differential diagnosis, and current approaches to management of HAE-C1-INH.

Factor XII-independent activation of the bradykinin-forming cascade: Implications for the pathogenesis of hereditary angioedema types I and II.

BACKGROUND: We have previously reported that prekallikrein expresses an active site when it is bound to high-molecular-weight kininogen (HK) and can digest HK to produce bradykinin. The reaction is stoichiometric and inhibited by C1 inhibitor (C1-INH) or corn trypsin inhibitor. Addition of heat shock protein 90 leads to conversion of prekallikrein to kallikrein in a zinc-dependent reaction. OBJECTIVE: Our goal was to determine whether these reactions are demonstrable in plasma and distinguish them from activation through factor XII. METHODS: Plasma was incubated in polystyrene plates and assayed for kallikrein formation. C1-INH was removed from factor XII-deficient plasma by means of immunoadsorption. RESULTS: We demonstrate that prekallikrein-HK will activate to kallikrein in phosphate-containing buffers and that the rate is further accelerated on addition of heat shock protein 90. Prolonged incubation of plasma deficient in both factor XII and C1-INH led to conversion of prekallikrein to kallikrein and cleavage of HK, as was seen in plasma from patients with hereditary angioedema but not plasma from healthy subjects. CONCLUSIONS: These results indicate that C1-INH stabilizes the prekallikrein-HK complex to prevent HK cleavage either by prekallikrein or by prekallikrein-HK autoactivation to generate kallikrein. In patients with hereditary angioedema, kallikrein and bradykinin formation can occur without invoking factor XII activation, although the kallikrein formed can rapidly activate factor XII if it is surface bound.

Therapeutic management of hereditary angioedema due to C1 inhibitor deficiency.

Hereditary angioedema (HAE) due to C1 inhibitor (C1-INH) deficiency is a rare genetic disease characterized by recurrent swellings of the subcutaneous and submucosal tissues that can manifest as cutaneous edema, abdominal pain and laryngeal edema with airway obstruction. These symptoms have a significant impact on patients' quality of life. The reduction in C1-INH function leads to uncontrolled activation of the contact system and generation of bradykinin, the mediator of increased vascular permeability and edema formation. In the past, few treatment options were available; however, several new therapies with proven efficacy have recently become available to treat and prevent HAE attacks, such as plasma-derived and recombinant C1-INHs that replace the deficient protein, bradykinin receptor antagonist (icatibant) that blocks bradykinin activity and kallikrein inhibitor (ecallantide) that prevents bradykinin release. Such therapies can improve disease outcome. This article reviews the therapeutic management of HAE, which involves the treatment of acute attacks and prophylaxis.

In pursuit of excellence: an integrated care pathway for C1 inhibitor deficiency.

There are estimated to be approximately 1500 people in the United Kingdom with C1 inhibitor (C1INH) deficiency. At BartsHealth National Health Service (NHS) Trust we manage 133 patients with this condition and we believe that this represents one of the largest cohorts in the United Kingdom. C1INH deficiency may be hereditary or acquired. It is characterized by unpredictable episodic swellings, which may affect any part of the body, but are potentially fatal if they involve the larynx and cause significant morbidity if they involve the viscera. The last few years have seen a revolution in the treatment options that are available for C1 inhibitor deficiency. However, this occurs at a time when there are increased spending restraints in the NHS and the commissioning structure is being overhauled. Integrated care pathways (ICP) are a tool for disseminating best practice, for facilitating clinical audit, enabling multi-disciplinary working and for reducing health-care costs. Here we present an ICP for managing C1 inhibitor deficiency.

Current pharmacotherapy of bradykinin-mediated angioedema.

INTRODUCTION: Bradykinin-mediated angioedema is characterized by subcutaneous and/or submucosal edema formation without wheals and pruritus. It is linked to bradykinin-enhanced vascular permeability and, therefore, it does not respond to conventional measures, but requires specific therapy. AREAS COVERED: This summary briefly reviews the different types of bradykinin-mediated angioedema and its remedies. Therapy focuses on relieving edema, as well as on decreasing its incidence and severity. The modes of the actions of attenuated androgens and antifibrinolytics are not precisely known - these agents have been introduced on an empirical basis. Contemporary treatments, by contrast, have been purposely developed to inhibit bradykinin. Most experience pertains to angioedema resulting from C1-inhibitor deficiency, and the controlled studies have focused on the hereditary form of this disease type (HAE). The pathomechanisms of HAE with normal C1-inhibitor activity, as well as of angiotensin-converting enzyme inhibitor-releated, and of non-histaminergic idiopathic sporadic angioedemas are largely unknown. Appropriate laboratory methods for the diagnosis, or specific interventions for the therapy of these conditions are not available or only available off-label. EXPERT OPINION: In this case, diagnosis and management are challenging. The range of targeted therapeutic options has increased in recent years and includes measures to handle emergencies, prevent edematous episodes and manage additional types of bradykinin-mediated angioedema.

Hereditary angioedema attacks resolve faster and are shorter after early icatibant treatment.

BACKGROUND: Attacks of hereditary angioedema (HAE) are unpredictable and, if affecting the upper airway, can be lethal. Icatibant is used for physician- or patient self-administered symptomatic treatment of HAE attacks in adults. Its mode of action includes disruption of the bradykinin pathway via blockade of the bradykinin B(2) receptor. Early treatment is believed to shorten attack duration and prevent severe outcomes; however, evidence to support these benefits is lacking. OBJECTIVE: To examine the impact of timing of icatibant administration on the duration and resolution of HAE type I and II attacks. METHODS: The Icatibant Outcome Survey is an international, prospective, observational study for patients treated with icatibant. Data on timings and outcomes of icatibant treatment for HAE attacks were collected between July 2009-February 2012. A mixed-model of repeated measures was performed for 426 attacks in 136 HAE type I and II patients. RESULTS: Attack duration was significantly shorter in patients treated <1 hour of attack onset compared with those treated ≥ 1 hour (6.1 hours versus 16.8 hours [p<0.001]). Similar significant effects were observed for <2 hours versus ≥ 2 hours (7.2 hours versus 20.2 hours [p<0.001]) and <5 hours versus ≥ 5 hours (8.0 hours versus 23.5 hours [p<0.001]). Treatment within 1 hour of attack onset also significantly reduced time to attack resolution (5.8 hours versus 8.8 hours [p<0.05]). Self-administrators were more likely to treat early and experience shorter attacks than those treated by a healthcare professional. CONCLUSION: Early blockade of the bradykinin B(2) receptor with icatibant, particularly within the first hour of attack onset, significantly reduced attack duration and time to attack resolution.

Per-attack reporting of prodromal symptoms concurrent with C1-inhibitor treatment of hereditary angioedema attacks.

INTRODUCTION: Prodromal symptoms commonly precede hereditary angioedema (HAE) attacks. There is continuing interest in evaluating prodromes as treatment indicators, but a paucity of relevant data. This study was designed to prospectively identify prodomal characteristics in patients voluntarily reporting such information around the time of seeking treatment for an acute HAE attack. METHODS: Twenty-eight patients with HAE were enrolled in this survey, which was conducted in the context of an open-label study of treatment of HAE attacks with plasma-derived C1-inhibitor concentrate. At the time of treatment, patients were encouraged to answer survey questions about prodromal symptoms preceding that particular HAE attack. RESULTS: Twenty-one patients provided prodromal information for 253 treated HAE attacks. Seventy-one percent of patients (15/21) reported prodromes. Three patients accounted for approximately 80% of the attacks and 89% of the reported prodromal symptoms. Prodromes were experienced before 67.6% (171/253) of attacks, with a mean of 1.4 prodromes per attack. Fatigue was the most frequent prodrome (42% of attacks), followed by nausea (26%), and flu-like symptoms (22%). The median duration of a prodrome before an attack was 12 h (range, 0.33-24 h). CONCLUSIONS: Despite many limitations in the study design, these findings confirm that prodromes are frequently associated with HAE attacks in many patients and occur sufficiently early to allow time for treatment initiation. The frequency of "false positive" prodromal symptoms remains undetermined, and the authors captured data only on attacks severe enough to warrant treatment. Additional well-designed prospective studies are clearly needed to continue investigating the potential clinical relevance of prodromes.

Efficacy assessments in randomized controlled studies of acute therapy for hereditary angioedema.

Hereditary angioedema (HAE) is a rare disorder caused by a deficiency of C1 esterase inhibitor, characterized by recurrent, highly variable attacks of subcutaneous or submucosal edema that may affect multiple body sites. Clinical studies of acute HAE therapies have required the use of assessment tools to evaluate both pretreatment attack severity (baseline severity) and changes in symptom severity following treatment (treatment response). This article reviews the range of assessment tools used for efficacy determination of acute HAE therapies, based on a review of relevant clinical studies. Because the goal is relief of symptoms (rather than cure), patient-reported outcomes (PROs) form the basis of these tools. Tools used to evaluate baseline severity typically employ location-specific assessment of symptom severity, using either categorical descriptions (which may be converted into numerical variables) or a visual analog scale (VAS). Some studies define the initial or most symptomatic site as an "index" site for purposes of efficacy determination, while others (such as the Mean Symptom Complex Severity score used in clinical studies of ecallantide) use a composite score that reflects all sites. Assessment of treatment response typically employs the same tool(s) to evaluate baseline severity, and may be either time-based (e.g., time to achievement of minimal or no symptoms) or symptom-based (e.g., degree of symptom relief at predetermined time points). Although it is unlikely that therapies will be compared using identical assessment tools, prospective or retrospective validation ensures the adequacy and relevance of such tools, which should be taken into consideration when therapies are compared.

There is an increased risk of atherosclerosis in hereditary angioedema.

BACKGROUND: Hereditary angioedema is associated either with a deficiency in the amount or in the function of the C1 inhibitor (C1 INH). OBJECTIVE: In this study the endothelial function of HAE patients was investigated to evaluate the impact of hereditary C1-INH deficiency on atherosclerosis, which has not yet been established before. METHODS: A total of 26 patients (14 female, 12 male. Mean age: 38±13) diagnosed with HAE and 30 healthy controls were enrolled in the study. Measurement of coronary flow reserve (CFR) in the left anterior descending coronary artery was performed using transthoracic doppler harmonic echocardiography at baseline and following dipyridamol infusion. The intima-media thickness (IMT) in the carotid artery was measured using an echocardiographic system equipped with 10 MHz linear transducer (Vingmed System Five). RESULTS: The mean CFR value for the HAE patient group was significantly lower than that of the control group (p<0.001). The mean IMT was not found to be significantly different between the two groups, although it was slightly higher in the HAE patient group. No correlation was found between the CFR and the disease severity scores, nor was it shown between the CFR values and the duration of danazol treatment. CONCLUSION: Our results indicate that there is a microvascular endothelial dysfunction in HAE patients. Although carotid intima media thickness of these patients was not significantly increased, the presence of microvascular endothelial dysfunction might be regarded as an early indicator of a premature atherosclerosis.

Cross-talk between the complement and the kinin system in vascular permeability.

The endothelium is a continuous physical barrier that regulates coagulation and selective passage of soluble molecules and circulating cells through the vessel wall into the tissue. Due to its anatomic localization, the endothelium may establish contact with components of the complement, the kinin and the coagulation systems which are the main, though not exclusive, inducers of vascular leakage. Although the complement and the kinin systems may act independently, increasing evidence suggest that there is a crosstalk that involve different components of both systems. Activation is required for the function of the two systems which are involved in pathological conditions such as hereditary and acquired angioedema (AE) and vasculitidis. The aim of this review is to discuss the contribution of complement and kinin systems to vascular leakage and the cross-talk between the two systems in the development of AE. This clinical condition is characterized by episodic and recurrent local edema of subcutaneous and submucosal tissues and is due to inherited or acquired C1-INH deficiency. Although the pathogenesis of the swelling in patients with AE was originally thought to be mediated by C2, ample evidence indicate bradykinin (BK) as the most effective mediator even though the possibility that both the complement and the kinin-forming systems may contribute to the edema has not been completely excluded. BK induces endothelial leakage interacting with B2 receptors but other molecules may be involved in the onset and maintenance of AE. In this review we shall discuss the role of B1 receptors and gC1qR/p33 in addition to that of B2 receptors in the onset of AE attacks and the importance of these receptors as new possible molecular targets for therapy.

Type I hereditary angioedema in Taiwan -- clinical, biological features and genetic study.

BACKGROUND: Hereditary angioedema (HAE) is a rare, autosomal dominant inherited disease which is caused by a genetic deficiency of C1 esterase inhibitor (C1 INH). There have only been a few case reports in Taiwan to date. OBJECTIVE: To describe the clinical features of type I HAE in Taiwanese patients. METHODS: Three unrelated Taiwanese families with type I HAE are reported, and one case of a family from a review of PubMed was reviewed. Clinical manifestations, diagnostic examinations, management and genetic studies were analyzed. RESULTS: Including this report, 19 patients had low C1 INH and low C4 levels and were diagnosed with type I HAE. Only 11 (57.9%) patients were symptomatic. Recurrent skin swelling and edema over the four extremities or trunk were reported in all symptomatic patients (100%). 45.5% of the patients recalled laryngeal attacks and one patient died from asphyxia. 18.2% of the patients experienced abdominal symptoms. The age at the beginning of clinical symptoms ranged from 5 to 30 years (mean +/- SD: 20.82 +/- 7.88 years). The diagnosis tended to be delayed (range from 1 to 39 years; mean +/- SD: 8.45 +/- 11.04 years). Nine patients had a mutant C1 INH gene, and two patients received long-term prophylaxis with danazol. CONCLUSION: The prevalence of hereditary angioedema in Taiwan is low. Persons with low levels of C1 INH who were clinically symptomatic accounted for only 57.9% of the cases in our study, which is far lower than previous reports from other countries. Ethnic differences may be the reason for this finding. Further genomic studies are needed to elucidate the genetic penetrance of C1 INH deficiency in Taiwan.