Cold-induced urticarial autoinflammatory syndrome related to factor XII activation

Recent advances in the discovery and development of drugs targeting the kallikrein-kinin system

BACKGROUND

The kallikrein-kinin system is a key regulatory cascade involved in blood pressure maintenance, hemostasis, inflammation and renal function. Currently, approved drugs remain limited to the rare disease hereditary angioedema. However, growing interest in this system is indicated by an increasing number of promising drug candidates for further indications.

METHODS

To provide an overview of current drug development, a two-stage literature search was conducted between March and December 2023 to identify drug candidates with targets in the kallikrein-kinin system. First, drug candidates were identified using PubMed and Clinicaltrials.gov. Second, the latest publications/results for these compounds were searched in PubMed, Clinicaltrials.gov and Google Scholar. The findings were categorized by target, stage of development, and intended indication.

RESULTS

The search identified 68 drugs, of which 10 are approved, 25 are in clinical development, and 33 in preclinical development. The three most studied indications included diabetic retinopathy, thromboprophylaxis and hereditary angioedema. The latter is still an indication for most of the drug candidates close to regulatory approval (3 out of 4). For the emerging indications, promising new drug candidates in clinical development are ixodes ricinus-contact phase inhibitor for thromboprophylaxis and RZ402 and THR-149 for the treatment of diabetic macular edema (all phase 2).

CONCLUSION

The therapeutic impact of targeting the kallikrein-kinin system is no longer limited to the treatment of hereditary angioedema. Ongoing research on other diseases demonstrates the potential of therapeutic interventions targeting the kallikrein-kinin system and will provide further treatment options for patients in the future.

How to Build a Fire: The Genetics of Autoinflammatory Diseases

Systemic autoinflammatory diseases (SAIDs) are a heterogeneous group of disorders caused by excess activation of the innate immune system in an antigen-independent manner. Starting with the discovery of the causal gene for familial Mediterranean fever, more than 50 monogenic SAIDs have been described. These discoveries, paired with advances in immunology and genomics, have allowed our understanding of these diseases to improve drastically in the last decade. The genetic causes of SAIDs are complex and include both germline and somatic pathogenic variants that affect various inflammatory signaling pathways. We provide an overview of the acquired SAIDs from a genetic perspective and summarize the clinical phenotypes and mechanism(s) of inflammation, aiming to provide a comprehensive understanding of the pathogenesis of autoinflammatory diseases.

A Fully Self-Powered Wearable Leg Movement Sensing System for Human Health Monitoring

Energy-autonomous wearable human activity monitoring is imperative for daily healthcare, benefiting from long-term sustainable uses. Herein, a fully self-powered wearable system, enabling real-time monitoring and assessments of human multimodal health parameters including knee joint movement, metabolic energy, locomotion speed, and skin temperature, which are fully self-powered by highly-efficient flexible thermoelectric generators (f-TEGs) is proposed and developed. The wearable system is composed of f-TEGs, fabric strain sensors, ultra-low-power edge computing, and Bluetooth. The f-TEGs worn on the leg not only harvest energy from body heat and supply power sustainably for the whole monitoring system, but also serve as zero-power motion sensors to detect limb movement and skin temperature. The fabric strain sensor made by printing PEDOT: PSS on pre-stretched nylon fiber-wrapped rubber band enables high-fidelity and ultralow-power measurements on highly-dynamic knee movements. Edge computing is elaborately designed to estimate multimodal health parameters including time-varying metabolic energy in real-time, which are wirelessly transmitted via Bluetooth. The whole monitoring system is operated automatically and intelligently, works sustainably in both static and dynamic states, and is fully self-powered by the f-TEGs.

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.

Cold Urticaria Syndromes: Diagnosis and Management

Cold urticaria is a chronic condition causing episodic symptoms of cold-induced wheals or angioedema in response to direct or indirect exposure to cold temperatures. Whereas symptoms of cold urticaria are typically benign and self-limiting, severe systemic anaphylactic reactions are possible. Acquired, atypical, and hereditary forms have been described, each with variable triggers, symptoms, and responses to therapy. Clinical testing, including response to cold stimulation, helps define disease subtypes. More recently, monogenic disorders characterized by atypical forms of cold urticaria have been described. Here, we review the different forms of cold-induced urticaria and related syndromes and propose a diagnostic algorithm to aid clinicians in making a timely diagnosis for the appropriate management of these patients.

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.

Editorial: Kinin 2022 Meeting, Annecy, France

The Kinin 2022 meeting took place at the Imperial Palace, Annecy, France, from 5-8 June 2022 [...].

Factor XII Explored with AlphaFold - Opportunities for Selective Drug Development

Medical device associated thrombosis is an important clinical problem. This type of thrombosis can result from Factor XII (FXII) binding to non-natural surface materials and subsequent activation of the contact pathway. This drives the development of new therapeutic strategies to block this pathway and information on the structural properties of FXII should catalyse this quest. Presently, there is no publicly available crystal structure of full-length FXII. However, the AlphaFold Protein Structure Database provides a model structure. We here explore this model in combination with previous structure-function studies to identify opportunities for selective pharmacological blockade of the contribution of FXII in medical device associated thrombosis. Previous studies demonstrated that FXII activation is dependent on molecular cleavage after R353. We subsequently proposed that protein conformation protects this cleavage site to ensure zymogen quiescence and prevent inappropriate FXII activation. The AlphaFold model shows that a small loop containing R353 indeed is buried in the globular molecule. This is the result of intra-molecular interactions between the (N-terminal) Fibronectin type II domain, (central) kringle and (C-terminal) protease domain, in a structure that resembles a three-point harness. Furthermore, this interaction pushes the intermediate domains, as well as the flexible proline-rich region (PRR), outward while encapsulating R353 in the molecule. The outward directed positively charged patches are likely to be involved in binding to anionic surfaces. The binding of FXII to surfaces (and several monoclonal antibodies) acccelerates its activation by inducing conformational changes. For prevention of medical device associated thrombosis, it is therefore important to target the surface binding sites of FXII without causing structural changes.

Recent advances in factor XII structure and function

PURPOSE OF REVIEW

Factor XII (FXII), the precursor of the protease FXIIa, contributes to pathologic processes including angioedema and thrombosis. Here, we review recent work on structure-function relationships for FXII based on studies using recombinant FXII variants.

RECENT FINDINGS

FXII is a homolog of pro-hepatocyte growth factor activator (Pro-HGFA). We prepared FXII in which domains are replaced by corresponding parts of Pro-HGA, and tested them in FXII activation and activity assays. In solution, FXII and prekallikrein undergo reciprocal activation to FXIIa and kallikrein. The rate of this process is restricted by the FXII fibronectin type-2 and kringle domains. Pro-HGA replacements for these domains accelerate FXII and prekallikrein activation. When FXII and prekallikrein bind to negatively charged surfaces, reciprocal activation is enhanced. The FXII EGF1 domain is required for surface binding.

SUMMARY

We propose a model in which FXII is normally maintained in a closed conformation resistant to activation by intramolecular interactions involving the fibronectin type-2 and kringle domains. These interactions are disrupted when FXII binds to a surface through EGF1, enhancing FXII activation and prekallikrein activation by FXIIa. These observations have important implications for understanding the contributions of FXII to disease, and for developing therapies to treat thrombo-inflammatory disorders.

IL-1 and autoinflammatory disease: biology, pathogenesis and therapeutic targeting

Over 20 years ago, it was first proposed that autoinflammation underpins a handful of rare monogenic disorders characterized by recurrent fever and systemic inflammation. The subsequent identification of novel, causative genes directly led to a better understanding of how the innate immune system is regulated under normal conditions, as well as its dysregulation associated with pathogenic mutations. Early on, IL-1 emerged as a central mediator for these diseases, based on data derived from patient cells, mutant mouse models and definitive clinical responses to IL-1 targeted therapy. Since that time, our understanding of the mechanisms of autoinflammation has expanded beyond IL-1 to additional innate immune processes. However, the number and complexity of IL-1-mediated autoinflammatory diseases has also multiplied to include additional monogenic syndromes with expanded genotypes and phenotypes, as well as more common polygenic disorders seen frequently by the practising clinician. In order to increase physician awareness and update rheumatologists who are likely to encounter these patients, this review discusses the general pathophysiological concepts of IL-1-mediated autoinflammation, the epidemiological and clinical features of specific diseases, diagnostic challenges and approaches, and current and future perspectives for therapy.

Development of the Cold Urticaria Activity Score

BACKGROUND

Cold urticaria (ColdU) is a form of inducible urticaria where cold induces wheals and/or angioedema. The burden of disease is high and linked to trigger thresholds, exposure, and avoidance. There are presently no validated patient-reported outcome measures (PROMs) to assess and monitor disease activity. Our objective was to develop a disease-specific activity score for ColdU that is easy to administer and evaluate.

METHODS

A Cold Urticaria Activity Score (ColdUAS) questionnaire was developed, directed by PROM developing guidelines. After the generation of a conceptional framework, the item generation phase included the literature research on ColdU signs and symptoms and on comparable tools for similar diseases and 47 ColdU patient interviews. Subsequently, an impact analysis for content validity was performed. The final selection of items underwent expert review for face validity and cognitive debriefing.

RESULTS

The ColdUAS, a self-administered questionnaire for the prospective assessment of disease activity in patients with ColdU, consists of 4 items: 1. the frequency and severity of the signs (wheals and/or angioedema), 2. the frequency and severity of the symptoms (e.g., itch and burn), 3. the exposure to specific triggers, and 4. the avoidance of these triggers. The recall period for each item is the last 24 h.

CONCLUSIONS

The ColdUAS is the first disease-specific PROM to assess ColdU disease activity. It may help to better assess patients' disease status in routine clinical practice as well as in clinical trials. Anchor-based approaches are currently used to validate the ColdUAS.

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.

Autoinflammation: Interferonopathies and Other Autoinflammatory Diseases

The family of autoinflammatory diseases (AIDs) continues to expand and now includes over 40 genetically defined disorders. Their defining feature is a dysregulated inflammatory innate immune response. Many AIDs have overlapping clinical characteristics, and dermatological manifestations are common. Autoinflammatory features have also been recognized in more common dermatological conditions such as psoriasis. Furthermore, there is an increasing understanding that immunodeficiencies, autoimmune disorders, and even some allergic disorders share overlapping autoinflammatory features. The discovery that certain somatic mutations, arising within the bone marrow and restricted to the myeloid cell lineage can cause acquired AID heralds a new era of discoveries in this field.

Sex-specific differences in plasma levels of FXII, HK, and FXIIa-C1-esterase inhibitor complexes in community acquired pneumonia

Sex-dependent differences in immunity and coagulation play an active role in the outcome of community-acquired pneumonia (CAP). Contact phase proteins act at the crossroads between inflammation and coagulation thus representing a point of convergence in host defense against infection. Here, we measured the levels of factor XII (FXII), FXIIa-C1 esterase inhibitor (C1INH) complexes, and high molecular weight kininogen (HK) in plasma of CAP patients and correlated them to clinical disease severity. Levels of FXIIa-C1INH/albumin ratio were elevated, irrespective of sex, in plasma of CAP patients (n=139) as compared to age-matched donors (n=58). No simultaneous decrease in FXII levels, indicating its consumption, was observed. Stratification by sex revealed augmented FXII levels in plasma of CAP women as compared to sex-matched donors yet no apparent differences in men. This sex-specific effect was, however, attributable to lower FXII levels in female donors relative to men donors. Plasma estradiol levels mirrored those for FXII. Levels of HK/albumin ratio were decreased in CAP plasma as compared to donors, however, after stratification by sex, this difference was only observed in women and was related to higher HK/albumin values in female donors as opposed to male donors. Finally, strong negative correlation between plasma levels of HK/albumin ratio and CAP severity, as assessed by CRB65 score, in males and females was observed. Our study identifies sex-dependent differences in plasma levels of the contact phase proteins in elderly subjects that may contribute to specific clinical outcomes in CAP between men and women.

Illustrated State-of-the-Art Capsules of the ISTH 2020 Congress

This year's Congress of the International Society of Thrombosis and Haemostasis (ISTH) was hosted virtually from Philadelphia July 17-21, 2021. The conference, now held annually, highlighted cutting-edge advances in basic, population and clinical sciences of relevance to the Society. Despite being held virtually, the 2021 congress was of the same scope and quality as an annual meeting held in person. An added feature of the program is that talks streamed at the designated times will then be available on-line for asynchronous viewing. The program included 77 State of the Art (SOA) talks, thematically grouped in 28 sessions, given by internationally recognized leaders in the field. The SOA speakers were invited to prepare brief illustrated reviews of their talks that were peer reviewed and are included in this article. The topics, across the main scientific themes of the congress, include Arterial Thromboembolism, Coagulation and Natural Anticoagulants, COVID-19 and Coagulation, Diagnostics and Omics, Fibrinogen, Fibrinolysis and Proteolysis, Hemophilia and Rare Bleeding Disorders, Hemostasis in Cancer, Inflammation and Immunity, Pediatrics, Platelet Disorders, von Willebrand Disease and Thrombotic Angiopathies, Platelets and Megakaryocytes, Vascular Biology, Venous Thromboembolism and Women's Health. These illustrated capsules highlight the major scientific advances with potential to impact clinical practice. Readers are invited to take advantage of the excellent educational resource provided by these illustrated capsules. They are also encouraged to use the image in social media to draw attention to the high quality and impact of the science presented at the congress.

Blood Clotting and the Pathogenesis of Types I and II Hereditary Angioedema

The plasma contact system is the initiator of the intrinsic pathway of coagulation and the main producer of the inflammatory peptide bradykinin. When plasma is exposed to a negatively charged surface the two enzymes factor XII (FXII) and plasma prekallikrein (PK) bind to the surface alongside the co-factor high molecular weight kininogen (HK), where PK is non-covalently bound to. Here, FXII and PK undergo a reciprocal activation feedback loop that leads to full contact system activity in a matter of seconds. Although naturally occurring negatively charged surfaces have shown to be involved in the role of the contact system in thrombosis, such surfaces are elusive in the pathogenesis of bradykinin-driven hereditary angioedema (HAE). In this review, we will explore the molecular mechanisms behind contact system activation, their assembly on the endothelial surface, and their role in the HAE pathophysiology.

Capillary electrophoresis as a fragment screening tool to cross-validate hits from chromogenic assay: Application to FXIIa

In this study, a partial-filling affinity capillary electrophoresis (pf-ACE) method was developed for the cross-validation of fragment hits revealed by chromogenic factor XIIa (FXIIa) assay. Chromogenic assay produces false positives, mainly due to spectrophotometric interferences and sample purity issues. pf-ACE was selected as counter-screening technology because of its separative character and the fact that the target does not have to be attached or tagged. The effects of protein plug length, applied voltage and composition of the running buffer were examined and optimized. Detection limit in terms of dissociation constant was estimated at 400 μM. The affinity evaluation was performed close to physiological conditions (pH 7.4, ionic strength 0.13 mol L^-1) in a poly (ethylene oxide)-coated capillary of 75 μm internal diameter x 33 cm length with an applied voltage of 3 kV. This method uncovered chromogenic assay's false positives due to zinc contamination. Moreover, pf-ACE supported the evaluation of compounds absorbing at 405 nm.

Cold urticaria - What we know and what we do not know

Cold urticaria (ColdU) is a common form of chronic inducible urticaria characterized by the development of wheals, angioedema or both in response to cold exposure. Recent research and guideline updates have advanced our understanding and management of ColdU. Today, its pathophysiology is thought to involve the cold-induced formation of autoallergens and IgE to these autoallergens, which provoke a release of proinflammatory mediators from skin mast cells. The classification of ColdU includes typical and atypical subtypes. We know that cold-induced wheals usually develop on rewarming and resolve within an hour and that anaphylaxis can occur. The diagnosis relies on the patient's history and cold stimulation testing. Additional diagnostic work-up, including a search for underlying infections, should only be done if indicated by the patient's history. The management of ColdU includes cold avoidance, the regular use of nonsedating antihistamines and the off-label use of omalizumab. However, many questions regarding ColdU remain unanswered. Here, we review what is known about ColdU, and we present important unanswered questions on the epidemiology, underlying pathomechanisms, clinical heterogeneity and treatment outcomes. Our aim is to guide future efforts that will close these knowledge gaps and advance the management of ColdU.

Monogenic autoinflammatory disorders: Conceptual overview, phenotype, and clinical approach

Autoinflammatory diseases are conditions in which pathogenic inflammation arises primarily through antigen-independent hyperactivation of immune pathways. First recognized just over 2 decades ago, the autoinflammatory disease spectrum has expanded rapidly to include more than 40 distinct monogenic conditions. Related mechanisms contribute to common conditions such as gout and cardiovascular disease. Here, we review the basic concepts underlying the "autoinflammatory revolution" in the understanding of immune-mediated disease and introduce major categories of monogenic autoinflammatory disorders recognized to date, including inflammasomopathies and other IL-1-related conditions, interferonopathies, and disorders of nuclear factor kappa B and/or aberrant TNF activity. We highlight phenotypic presentation as a reflection of pathogenesis and outline a practical approach to the evaluation of patients with suspected autoinflammation.

Hereditary Hearing Impairment with Cutaneous Abnormalities

Syndromic hereditary hearing impairment (HHI) is a clinically and etiologically diverse condition that has a profound influence on affected individuals and their families. As cutaneous findings are more apparent than hearing-related symptoms to clinicians and, more importantly, to caregivers of affected infants and young individuals, establishing a correlation map of skin manifestations and their underlying genetic causes is key to early identification and diagnosis of syndromic HHI. In this article, we performed a comprehensive PubMed database search on syndromic HHI with cutaneous abnormalities, and reviewed a total of 260 relevant publications. Our in-depth analyses revealed that the cutaneous manifestations associated with HHI could be classified into three categories: pigment, hyperkeratosis/nail, and connective tissue disorders, with each category involving distinct molecular pathogenesis mechanisms. This outline could help clinicians and researchers build a clear atlas regarding the phenotypic features and pathogenetic mechanisms of syndromic HHI with cutaneous abnormalities, and facilitate clinical and molecular diagnoses of these conditions.

A Pathophysiological Perspective on the SARS-CoV-2 Coagulopathy

Recent evidence is focusing on the presence of a hypercoagulable state with development of both venous and arterial thromboembolic complications in patients infected with SARS-CoV-2. The ongoing activation of coagulation related to the severity of the illness is further characterized by thrombotic microangiopathy and endotheliitis. These microangiopathic changes cannot be classified as classical disseminated intravascular coagulation (DIC). In this short review we describe the interaction between coagulation and inflammation with focus on the possible mechanisms that might be involved in SARS-CoV-2 infection associated coagulopathy in the critically ill.

Cold-induced urticarial autoinflammatory syndrome related to factor XII activation

Hereditary autoinflammatory diseases are caused by gene mutations of the innate immune pathway, e.g. nucleotide receptor protein 3 (NLRP3). Here, we report a four-generation family with cold-induced urticarial rash, arthralgia, chills, headache and malaise associated with an autosomal-dominant inheritance. Genetic studies identify a substitution mutation in gene F12 (T859A, resulting in p.W268R) which encodes coagulation factor XII (FXII). Functional analysis reveals enhanced autocatalytic cleavage of the mutated protein and spontaneous FXII activation in patient plasma and in supernatant of transfected HEK293 cells expressing recombinant W268R-mutated proteins. Furthermore, we observe reduced plasma prekallikrein, cleaved high molecular weight kininogen and elevated plasma bradykinin. Neutrophils are identified as a local source of FXII. Interleukin-1β (IL-1β) is upregulated in lesional skin and mononuclear donor cells exposed to recombinant mutant proteins. Treatment with icatibant (bradykinin-B2-antagonist) or anakinra (interleukin-1-antagonist) reduces disease activity in patients. In conclusion, our findings provide a link between contact system activation and cytokine-mediated inflammation.

Systemic autoinflammatory syndromes such as cryopyrin-associated periodic syndrome (CAPS) are rare and often involve genes related to the inflammasome. Here, the authors report a syndrome characterised by systemic inflammation and cold-induced urticarial rash associated with a Factor XII-activating mutation.