[Cryopyrin-associated periodic syndromes]

Pathogenic variants in the NLRP3 LRR domain at position 861 are responsible for a boost-dependent atypical CAPS phenotype

BACKGROUND

Cryopyrin-associated periodic syndrome (CAPS) is associated with NLRP3 pathogenic variants, mostly located in the NACHT (neuronal apoptosis inhibitor protein, MHC class 2 transcription activator, incompatibility locus protein from Podospora anserina, telomerase-associated protein) domain. Cold-induced urticarial rash is among the main clinical features. However, this study identified a series of 14 patients with pathogenic variants of the Y861 residue (p.Tyr861) of the LRR domain of NLRP3 and minimal prevalence of cold-induced urticarial rash.

OBJECTIVES

This study aimed to address a possible genotype/phenotype correlation for patients with CAPS and to investigate at the cellular levels the impact of the Y861C substitution (p.Tyr861Cys) on NLRP3 activation.

METHODS

Clinical features of 14 patients with CAPS and heterozygous substitution at position 861 in the LRR domain of NLRP3 were compared to clinical features of 48 patients with CAPS and pathogenic variants outside the LRR domain of NLRP3. IL-1β secretion by PBMCs and purified monocytes from patients and healthy donors was evaluated following LPS and monosodium urate crystal stimulation.

RESULTS

Patients with substitution at position 861 of NLRP3 demonstrated a higher prevalence of sensorineural hearing loss while being less prone to skin urticarial. In contrast to patients with classical CAPS, cells from patients with a pathogenic variant at position 861 required an activation signal to secrete IL-1β but produced more IL-1β during the early and late phase of secretion than cells from healthy donors.

CONCLUSIONS

Pathogenic variants of Y861 of NLRP3 drive a boost-dependent oversecretion of IL-1β associated with an atypical CAPS phenotype.

MicroRNAs in inflammasomopathies

microRNAs (miRNAs) are small non-coding RNA sequences that negatively regulate the expression of protein-encoding genes at the post-transcriptional level. They play a role in the regulation of inflammatory responses by controlling the proliferation and activation of immune cells and their expression is disrupted in several immune-mediated inflammatory disorders. Among these, autoinflammatory diseases (AID) are a group of rare hereditary disorders caused by abnormal activation of the innate immune system and characterized by recurrent fevers. Major groups of AID are inflammasomopathies, which are associated with hereditary defects in the activation of inflammasomes, cytosolic multiprotein signaling complexes regulating IL-1 family cytokine maturation and pyroptosis. The study of the role of miRNAs in AID is only recently emerging and remains scarce in inflammasomopathies. In this review, we describe the AID and inflammasomopathies, and the current knowledge on the role of miRNAs in disease processes.

Immunogenetics of the Ocular Anterior Segment: Lessons from Inherited Disorders

Autoimmune and autoinflammatory diseases cause morbidity in multiple organ systems including the ocular anterior segment. Genetic disorders of the innate and adaptive immune system present an avenue to study more common inflammatory disorders and host-pathogen interactions. Many of these Mendelian disorders have ophthalmic manifestations. In this review, we highlight the ophthalmic and molecular features of disorders of the innate immune system. A comprehensive literature review was performed using PubMed and the Online Mendelian Inheritance in Man databases spanning 1973-2020 with a focus on three specific categories of genetic disorders: RIG-I-like receptors and downstream signaling, inflammasomes, and RNA processing disorders. Tissue expression, clinical associations, and animal and functional studies were reviewed for each of these genes. These genes have broad roles in cellular physiology and may be implicated in more common conditions with interferon upregulation including systemic lupus erythematosus and type 1 diabetes. This review contributes to our understanding of rare inherited conditions with ocular involvement and has implications for further characterizing the effect of perturbations in integral molecular pathways.

Monogenic Autoinflammatory Diseases: State of the Art and Future Perspectives

Systemic autoinflammatory diseases are a heterogeneous family of disorders characterized by a dysregulation of the innate immune system, in which sterile inflammation primarily develops through antigen-independent hyperactivation of immune pathways. In most cases, they have a strong genetic background, with mutations in single genes involved in inflammation. Therefore, they can derive from different pathogenic mechanisms at any level, such as dysregulated inflammasome-mediated production of cytokines, intracellular stress, defective regulatory pathways, altered protein folding, enhanced NF-kappaB signalling, ubiquitination disorders, interferon pathway upregulation and complement activation. Since the discover of pathogenic mutations of the pyrin-encoding gene MEFV in Familial Mediterranean Fever, more than 50 monogenic autoinflammatory diseases have been discovered thanks to the advances in genetic sequencing: the advent of new genetic analysis techniques and the discovery of genes involved in autoinflammatory diseases have allowed a better understanding of the underlying innate immunologic pathways and pathogenetic mechanisms, thus opening new perspectives in targeted therapies. Moreover, this field of research has become of great interest, since more than a hundred clinical trials for autoinflammatory diseases are currently active or recently concluded, allowing us to hope for considerable acquisitions for the next few years. General paediatricians need to be aware of the importance of this group of diseases and they should consider autoinflammatory diseases in patients with clinical hallmarks, in order to guide further examinations and refer the patient to a specialist rheumatologist. Here we resume the pathogenesis, clinical aspects and diagnosis of the most important autoinflammatory diseases in children.

Cellular Models and Assays to Study NLRP3 Inflammasome Biology

The NLRP3 inflammasome is a multi-protein complex that initiates innate immunity responses when exposed to a wide range of stimuli, including pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs). Inflammasome activation leads to the release of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18 and to pyroptotic cell death. Over-activation of NLRP3 inflammasome has been associated with several chronic inflammatory diseases. A deep knowledge of NLRP3 inflammasome biology is required to better exploit its potential as therapeutic target and for the development of new selective drugs. To this purpose, in the past few years, several tools have been developed for the biological characterization of the multimeric inflammasome complex, the identification of the upstream signaling cascade leading to inflammasome activation, and the downstream effects triggered by NLRP3 activation. In this review, we will report cellular models and cellular, biochemical, and biophysical assays that are currently available for studying inflammasome biology. A special focus will be on those models/assays that have been used to identify NLRP3 inhibitors and their mechanism of action.

Systemic autoinflammatory diseases: Clinical state of the art

Systemic autoinflammatory diseases (SAIDs) are defined as disorders of innate immunity. They were initially defined in opposition to autoimmune diseases due to the lack of involvement of the adaptive immune system and circulating autoantibodies. The four historical monogenic diseases are familial Mediterranean fever (associated with MEFV mutations), cryopyrinopathies (NLRP3 mutations), tumor necrosis factor receptor-associated periodic syndrome (TNFRSF1A mutations), and mevalonate kinase deficiency (MVK mutations). In the last 10 years, more than 50 new monogenic SAIDs have been discovered thanks to advances in genetics. Diagnosis is largely based on personal and family history and detailed analysis of signs and symptoms associated with febrile attacks, in the setting of elevated inflammatory markers. Increasingly efficient techniques of genetic analysis can contribute to refining the diagnosis. This review is a guide for the clinician in suspecting and establishing a diagnosis of SAID.

Cryopyrin-associated periodic fever syndrome in children: A case-based review

Cryopyrin-associated periodic fever syndrome (CAPS) represents an increasingly recognized disease group entity, with varied presentations. CAPS includes 3 clinical entities, namely, familial cold-induced autoinflammatory syndrome (FCAS; MIM #120100), Muckle-Wells syndrome (MWS; MIM #191900) and chronic inflammatory neurologic cutaneous and articular syndrome (CINCA; MIM #607115); which share several overlapping clinical features. These patients often present with early-onset episodes of fever and rash, and variable systemic signs and symptoms, making it a great mimicker of other systemic autoimmune diseases. The episodes are transient and related to exposure to cold temperature and worsen in the winter season. We hereby present a case presenting with recurrent seasonal fever and rash, diagnosed as FCAS/ MWS overlap based on clinical signs and symptoms and positive testing for NLRP3 gene mutation. We also discuss the clinical presentation and complications of CAPS, chiefly FCAS and MWS, along with the previously described pediatric cases of CAPS. We tried to review the complexities of management of such patients, including the genetic diagnosis and the role of biological therapy. Based on the review of the literature, given the evident broad spectrum of symptoms and signs, use of next-generation sequencing can help in prompt diagnosis and early initiation of biological agents, which may play a great role in reducing the complications that these patients may experience in the long run.

Autoinflammatory diseases: State of the art

Autoinflammatory diseases are characterized by innate immunity abnormalities. In autoinflammatory diseases (AID), inflammatory blood biomarkers are elevated during crisis without infection and usually without autoantibodies. The first 4 described AID were familial Mediterranean fever, cryopyrin-associated periodic fever syndrome (CAPS) or NLRP3-associated autoinflammatory disease (NRLP3-AID), mevalonate kinase deficiency (MKD) and TNFRSF1A-receptor associated periodic fever syndrome (TRAPS). Since their description 20 years ago, and with the progresses of genetic analysis, many new diseases have been discovered; some with recurrent fever, others with predominant cutaneous symptoms or even immune deficiency. After describing the 4 historical recurrent fevers, some polygenic inflammatory diseases will also be shortly described such as Still disease and periodic fever with adenitis, pharyngitis and aphtous (PFAPA) syndrome. To better explore AID, some key anamnesis features are crucial such as the family tree, the age at onset, crisis length and organs involved in the clinical symptoms. An acute phase response is mandatory in crisis.