Brief report: genotype, phenotype, and clinical course in five patients with PAPA syndrome (pyogenic sterile arthritis, pyoderma gangrenosum, and acne)

Pediatric Neutrophilic Dermatoses

The term neutrophilic dermatosis encompasses a heterogeneous group of diseases, often associated with an underlying internal noninfectious disease, with an overlapping histopathologic background characterized by perivascular and diffuse neutrophilic infiltrates in one or more layers of the skin; extracutaneous neutrophilic infiltrates may be associated. Neutrophilic dermatoses are not frequent in children and, when they appear in this age group, represent a diagnostic and therapeutic challenge. Apart from the classic neutrophilic dermatoses such as pyoderma gangrenosum, Sweet syndrome, and Behçet disease, a neutrophilic dermatosis can be the presentation of rare genetic diseases of the innate immune system, such as autoinflammatory diseases.

Genetic mutations in pyoderma gangrenosum, hidradenitis suppurativa, and associated autoinflammatory syndromes: Insights into pathogenic mechanisms and shared pathways

Pyoderma gangrenosum (PG), hidradenitis suppurativa (HS), and the associated autoinflammatory syndromes, including pyogenic arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome, PSTPIP1-associated myeloid-related proteinemia inflammatory (PAMI) syndrome, pyoderma gangrenosum, acne, and hidradenitis suppurativa (PASH) syndrome, and pyogenic arthritis, pyoderma gangrenosum, acne, and suppurative hidradenitis (PAPASH) syndrome are dermatological conditions characterized by chronic inflammation and tissue damage. Recent advances in genetic research have identified specific mutations associated with these disorders, shedding light on their underlying pathogenic mechanisms. This review aims to summarize the current knowledge of identified mutations and presumed pathophysiology in PG, HS, and the associated autoinflammatory syndromes.

Detection of a rare variant in PSTPIP1 through three generations in a family with an initial diagnosis of FMF/MKD-overlapping phenotype

OBJECTIVE

The presence of FMF cases without MEFV (MEFV innate immunity regulator, pyrin) pathogenic variants led us to search for other genes' involvement in the disease development. Here, we describe the presence of genetic heterogeneity in a three-generation family with an FMF/mevalonate kinase deficiency (MKD)-overlapping phenotype without MEFV/MVK (mevalonate kinase) pathogenic variants.

METHOD

Targeted sequencing revealed a rare, fully penetrant variant in PSTPIP1 (p.Arg228Cys, rs781341816). Computational stability analyses of PSTPIP1 protein were performed. PSTPIP1-pyrin protein interaction was examined by immunoprecipitation and immunoblotting in peripheral blood mononuclear cells (PBMCs) of patients and healthy controls. PBMCs were cultured, and inflammation was induced by LPS+ATP treatment, followed by protein level measurements of caspase-1, IL1ß, pyrin and PSTPIP1 in cell lysates and mature caspase-1 and mature IL1ß in supernatants.

RESULTS

The conserved, rare (GnomAD, 0.000028) PSTPIP1 p.Arg228Cys variant, previously reported in ClinVar as a variant with uncertain significance, showed complete penetrance in the family presenting an autosomal dominant pattern. Computational analyses showed a potentially destabilizing effect of the variant on PSTPIP1 protein. Accordingly, PSTPIP1-pyrin interaction was increased in patients harboring the variant, which resulted in elevated levels of mature caspase-1 and IL1ß in the inflammation-induced patient samples.

CONCLUSIONS

Unlike previously described cases with pyogenic arthritis, pyoderma gangrenosum, and acne (PAPA)-associated PSTPIP1 variants, our patients with the p.Arg228Cys variant presented with an FMF/MKD-overlapping phenotype. As additional data on the genetic heterogeneity in the variable clinical spectrum of autoinflammatory syndromes, we suggest that the p.Arg228Cys variant in PSTPIP1 is related to inflammation responses through strong PSTPIP1-pyrin interaction and pyrin inflammasome activation.

PSTPIP1-Associated Myeloid-Related Proteinemia Inflammatory (PAMI) Syndrome: A Systematic Review

PSTPIP1 (proline-serine-threonine phosphatase-interactive protein 1)-associated myeloid-related proteinemia inflammatory (PAMI) syndrome, previously known as Hyperzincemia/Hypercalprotectinemia (Hz/Hc) syndrome, is a recently described, rare auto-inflammatory disorder caused by specific deleterious variants in the PSTPIP1 gene (p.E250K and p.E257K). The disease is characterized by chronic systemic inflammation, cutaneous and osteoarticular manifestations, hepatosplenomegaly, anemia, and neutropenia. Increased blood levels of MRP 8/14 and zinc distinguish this condition from other PSTPIP1-associated inflammatory diseases (PAID). The aim of this systematic review is to provide a comprehensive overview of the disease phenotype, course, treatment, and outcome based on reported cases. This systematic review adheres to the PRISMA guidelines (2020) for reporting. A literature search was performed in Embase, Medline, and Web of Science on 13 October 2022. The quality of the case reports and case series was assessed using the JBI checklists. Out of the 43 included patients with PAMI syndrome, there were 24 females and 19 males. The median age at onset was 3.9 years. The main clinical manifestations included anemia (100%), neutropenia (98%), cutaneous manifestations (74%), osteoarticular manifestations (72%), splenomegaly (70%), growth failure (57%), fever (51%), hepatomegaly (56%), and lymphadenopathy (39%). Systemic inflammation was described in all patients. Marked elevation of zinc and MRP 8/14 blood levels were observed in all tested patients. Response to treatment varied and no consistently effective therapy was identified. The most common therapeutic options were corticosteroids (N = 30), anakinra (N = 13), cyclosporine A (N = 11), canakinumab (N = 6), and anti-TNF (N = 14). Hematopoietic stem cell transplantation has been recently reported to be successful in five patients. Our review highlights the key characteristics of PAMI syndrome and the importance of considering this disease in the differential diagnosis of patients presenting with early-onset systemic inflammation and cytopenia.

Pediatric autoinflammatory bone disorders-a mini review with special focus on pathogenesis and inborn errors of immunity

Autoinflammatory bone disorders are a group of diseases characterized by sterile osteomyelitis. This includes chronic nonbacterial osteomyelitis and the monogenic forms, Majeed syndrome and deficiency of the interleukin-1 receptor antagonist. These disorders result from innate immune system dysregulation and cytokine imbalance that triggers inflammasome activation causing downstream osteoclastogenesis and excessive bone remodeling. In this review, we will summarize the immunopathogenesis of pediatric autoinflammatory bone diseases with a special focus on the genetics and inborn errors of immunity, while briefly touching on the clinical manifestations and management of each disease as well as areas for future research.

Rare missense variants in the SH3 domain of PSTPIP1 are associated with hidradenitis suppurativa

Hidradenitis suppurativa (HS) is a chronic, debilitating skin disease for which few treatment options are available. While most HS is sporadic, some rare kindred show a high-penetrance, autosomal-dominant inheritance. We wanted to identify rare variants that could contribute to HS risk in sporadic cases using candidate gene sequencing. We ultimately identified 21 genes for our capture panel. We included genes of the γ-secretase complex (n = 6) because rare variants in these genes sometimes cause familial HS. We added Notch receptor and ligand genes (n = 13) because γ-secretase is critical for processing Notch receptor signaling. Clinically, some people with PAPA (pyogenic arthritis, pyoderma gangrenosum, and acne) syndrome, a rare inflammatory disease, have concurrent HS. Rare variants in PSTPIP1 are known to cause PAPA syndrome, so we included PSTPIP1 and PSTPIP2 in the capture panel. We screened 117 individuals with HS for rare variations and calculated the expected burden using Genome Aggregation Database (gnomAD) allele frequencies. We discovered two pathogenic loss-of-function variants in NCSTN. This class of NCSTN variant can cause familial HS. There was no increased burden of rare variations in any γ-secretase complex gene. We did find that individuals with HS had a significantly increased number of rare missense variants in the SH3 domain of PSTPIP1. This finding, therefore, implicates PSTPIP1 variation in sporadic HS and further supports dysregulated immunity in HS. Our data also suggests that population-scale HS genetic research will yield valuable insights into disease pathology.

PSTPIP1-associated myeloid-related proteinaemia inflammatory (PAMI) syndrome; a case presenting as a perinatal event with early central nervous system involvement?

BACKGROUND

We report a three-year-old girl with a potentially unique phenotype of perinatal onset and neurovascular features who was found to have PAMI syndrome. We also compare her case to those previously reported and review the differences between the PSTPIP1-associated inflammatory diseases (PAID) phenotypes and genotypes.

CASE PRESENTATION

The patient was found to have a heterozygous pathogenic variant in PSTPIP1 (c.748G > A p.E250K). This variant was shown to be absent in both parents and therefore de novo in the patient. A literature review was carried out through multiple databases using the terms PSTPIP1, PAID, PAPA syndrome and PAMI syndrome. This information was collected and used to form comparisons between the current literature and our reported case.

CONCLUSIONS

Our case contributes to the literature on PAMI syndrome whilst providing an example of a potentially unique clinical phenotype, giving insight into the pre-symptomatic phase of the condition. We highlight the importance of considering PAMI syndrome in the differential for early onset unexplained inflammation. In addition, we explore the possibility that perinatal neurovascular events could be an early feature of PAMI syndrome.

Biologic Therapies for the Management of Cutaneous Findings in Genodermatoses: A Review

Genodermatoses are genetically inherited dermatologic conditions. The management of cutaneous findings in genodermatoses is challenging, and first-line therapies, such as steroids and/or retinoids, are often inadequate. In recent years, research on the molecular basis of genodermatoses has led to the use of biologic therapies for intractable disease. Here, we review the evidence regarding the use of available biologic therapies for the management of dermatologic findings in genodermatoses. Biologic therapies appear to be promising therapeutic options for several recalcitrant genodermatoses, especially those with underlying immune dysregulation. However, not all genodermatoses are amenable to biologic therapies, and some have been shown to paradoxically worsen under treatment. Biologic therapies offer a novel avenue to target refractory genodermatoses. However, evidence supporting the use of biologic therapies in the management of genodermatoses is mostly limited to case reports and case series. Further studies are warranted to determine the safety and efficacy of biologic therapies for the management of cutaneous findings in genodermatoses.

The genetics behind inflammasome regulation

The inflammasome is a cytosolic multiproteic complex that promotes proinflammatory events through the release of the cytokines IL-1β and IL-18, and in some context by the induction of a lytic cell death called pyroptosis, in response to damage, infections, or changes in the homeostasis. Due to the powerful inflammatory effect, there are several regulatory mechanisms that are essential to modulate or limit the activation of the inflammasome. When these mechanisms fail, the deregulation of the complex leads or contributes to the development of a plethora of diseases characterized by constitutive and/or chronic inflammation, such as autoinflammatory, autoimmune, cardiovascular, neurodegenerative, and metabolic diseases, cancer, or even severe complications of infectious diseases. Either environmental or genetic factors may affect the threshold and/or the level of inflammasome activation, such as hyperglycemia, hyperuricemia, auto-antibodies, unfolded proteins and fibrils, or individual genetic variants in genes coding for inflammasome receptors or effector molecules, and also in regulators. While the genetics of inflammasome itself has been elsewhere characterized and also recently reviewed by our group, less is known about how genetic variants in regulatory molecules could affect inflammatory diseases. Therefore in this work, we selected a group of known or possible regulators of the inflammasome, and through the review of genetic association studies we tried to depict the contribution of these regulators in the development of multifactorial diseases.

Pyoderma Gangrenosum: A Systematic Review of the Molecular Characteristics of Disease

Pyoderma Gangrenosum is a painful recurrent ulcerative neutrophilic dermatosis in which the pathogenesis is incompletely defined. Current evidence suggests that PG is associated with dysregulation of components of both the innate and adaptive immune system with dysregulation of neutrophil function and contribution of the Th17 immune axis. PG can present in numerous heterogeneous clinical presentations and be associated with multiple inflammatory conditions including Rheumatoid Arthritis, inflammatory bowel disease and hidradenitis suppurativa. However, no critical evaluation of the observed molecular characteristics in PG studies in association with their clinical findings has been assessed. Additionally, emerging evidence suggests a potential role for other cell types and immune pathways including B cells, macrophages, autoantibodies, and the complement system in PG although these have not yet been integrated into the pathogenesis of disease. This systematic review aims to critically evaluate the current molecular observations regarding the pathogenesis of PG and discuss associations with clinical characteristics as well as the evidence supporting novel cell types and immune pathways in PG.

Excess Serum Interleukin-18 Distinguishes Patients With Pathogenic Mutations in PSTPIP1

OBJECTIVE

Dominantly inherited PSTPIP1 mutations cause a spectrum of autoinflammatory manifestations epitomized by PAPA syndrome (pyogenic sterile arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome.). The connections between PSTPIP1 and PAPA syndrome are poorly understood, although evidence suggests involvement of pyrin inflammasome activation. Interleukin-18 (IL-18) is an inflammasome-activated cytokine associated with susceptibility to macrophage activation syndrome (MAS). This study was undertaken to investigate an association of IL-18 with PAPA syndrome.

METHODS

Clinical and genetic data and serum samples were obtained from patients referred to institutions due to symptoms indicative of PAPA syndrome. Serum IL-18, IL-18 binding protein (IL-18BP), and CXCL9 levels were assessed by bead-based assay, and free IL-18 levels were assessed by enzyme-linked immunosorbent assay.

RESULTS

The symptoms of PSTPIP1-positive patients with PAPA syndrome overlapped with those of mutation-negative patients with PAPA-like conditions, but mutation-positive patients had earlier onset and a greater proportion had a history of arthritis. We found uniform elevation of total serum IL-18 in treated PAPA syndrome patients at levels nearly as high as those seen in NLRC4-associated autoinflammation with infantile enterocolitis patients, and well above levels found in most familial Mediterranean fever patients. Serum IL-18 elevation in PAPA syndrome patients persisted despite fluctuations in disease activity. Levels of the soluble IL-18 antagonist IL-18BP were modestly elevated, and PAPA syndrome patients had detectable free IL-18. PAPA syndrome was rarely associated with elevation of CXCL9, an indicator of interferon-γ activity, but no PAPA syndrome patients had a history of MAS.

CONCLUSION

PAPA syndrome is a refractory and often disabling monogenic autoinflammatory disease associated with chronic and unopposed elevation of serum IL-18 levels but not with risk of MAS. These findings affect our understanding of the diseases in which IL-18 is overproduced and suggest a link between pyrin inflammasome activation, IL-18, and autoinflammation, without susceptibility to MAS.

Cutaneous signs and mechanisms of inflammasomopathies

The emerging group of autoinflammatory diseases (AIDs) is caused by a dysregulation of the innate immune system while lacking the typical footprint of adaptive immunity. A prominent subgroup of AIDs are inflammasomopathies, which are characterised by periodic flares of cutaneous signs as well as systemic organ involvement and fever. The range of possible skin lesions is vast, ranging from urticarial, erysipelas-like and pustular rashes to erythematous patches, violaceous plaques and eventual necrosis and ulceration. This review provides a structured overview of the pathogenesis and the clinical picture with a focus on dermatological aspects of inflammasomopathies. Current treatment options for these conditions are also discussed.

Acne Syndromes and Mosaicism

Abnormal mosaicism is the coexistence of cells with at least two genotypes, by the time of birth, in an individual derived from a single zygote, which leads to a disease phenotype. Somatic mosaicism can be further categorized into segmental mosaicism and nonsegmental somatic mosaicism. Acne is a chronic illness characterized by inflammatory changes around and in the pilosebaceous units, commonly due to hormone- and inflammatory signaling-mediated factors. Several systemic disorders, such as congenital adrenal hyperplasia, polycystic ovarian syndrome, and seborrhoea-acne-hirsutism-androgenetic alopecia syndrome have classically been associated with acne. Autoinflammatory syndromes, including PAPA, PASH, PAPASH, PsAPASH, PsaPSASH, PASS, and SAPHO syndromes include acneiform lesions as a key manifestation. Mosaic germline mutations in the FGFR2 gene have been associated with Apert syndrome and nevus comedonicus, two illnesses that are accompanied by acneiform lesions. In this review, we summarize the concept of cutaneous mosaicism and elaborate on acne syndromes, as well as acneiform mosaicism.

Mutation in the proline-serine-threonine phosphatase-interacting protein 1 (PSTPIP1) gene in a patient with acute lymphoblastic leukemia

Autoinflammatory syndromes are disorders characterized by recurrent or chronic inflammation caused by the dysregulation of the innate immune system. Hemophagocytic lymphohistiocytosis (HLH) is an aggressive and life-threatening syndrome of overactivation of the immune system.

We present a case of a 20-month-old boy who was referred to an oncology clinic because of HLH suspicion. In the preceding time, our patient suffered from a severe form of chickenpox with prolonged fever. Tests including myelogram, cerebrospinal fluid, and magnetic resonance (MR) of the brain gave a diagnosis of acute lymphoblastic leukemia from B lymphocyte precursors, without occupying the central nervous system. To exclude inherited HLH in our patient, next-generation sequencing was performed, which revealed a heterozygous missense mutation in exon 15 of the PSTPIP1 gene (c.1213C>T, R405C). No mutations of genes associated with familial HLH syndrome were found.

Our patient may be evidence that autoinflammatory diseases caused by PSTPIP1 gene mutations are not limited to the classical pyogenic arthritis, pyoderma gangrenosum, and acne (PAPA) phenotype but may have a different clinical presentation, and the spectrum of the PSTPIP1-associated inflammatory diseases (PAID) syndrome is more extensive than previously thought.

Case Report: Pyogenic Arthritis, Pyoderma Gangrenosum, and Acne: A Single-Center Experience and Literature Review

Objectives

This study aims to describe the characteristics of patients diagnosed with pyogenic arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome at a single center in China and provide an up-to-date literature review.

Methods

The clinical data and genotype of three Chinese Han patients were carefully documented and studied. We also conducted a systematic literature review on PAPA syndrome.

Results

A total of three patients were diagnosed with PAPA syndrome at our center from 2018 to 2020. Arthritis was observed in all three patients, while pyoderma gangrenosum (PG) was found in two patients and acne in one patient. Other manifestations included pathergy reaction, intermittent fever, oral ulcer, keratitis, proteinuria, and hematuria. The PSTPIP1 A230T mutation was identified in two patients, and a novel Y119C variation was revealed in a sporadic patient. A total of 76 patients with PAPA syndrome reported in 29 articles were included in our literature review. The classical triad of arthritis, PG, and acne was visible in only 16 (25.4%) patients, while 24 (38.1%) exhibited only one major symptom. Skin lesions were more commonly seen in patients with adult-onset disease than those with childhood-onset disease (100 vs. 83%), whereas arthritis was less common (50 vs. 98.1%). Steroid and/or biological agents were effective in most patients.

Conclusions

The rarity and phenotypic heterogeneity associated with PAPA syndrome make the diagnosis a huge challenge to physicians, especially in adult patients. A significant portion of patients did not exhibit the full spectrum of the classical triad. Accordingly, gene testing is critically helpful for diagnosis.

Pyoderma Gangrenosum and Interleukin Inhibitors: A Semi-Systematic Review

BACKGROUND

Pyoderma gangrenosum (PG) is a rare ulcerating skin disease associated with multiple comorbidities and increased mortality. In recent decades, newer biologics such as interleukin inhibitors have been used to treat PG; however, the literature is scarce, consisting predominantly of case reports and caseseries. The aim of our review was to evaluate the effectiveness and safety of interleukin inhibitors for the treatment of PG in adults.

SUMMARY

A literature search was conducted using search terms related to PG and interleukin inhibitors in databases such as PubMed, Embase, Scopus, Web of Science, and Cochrane Library. The study eligibility criteria included patients diagnosed with PG, over the age of 18, and treated with an interleukin inhibitor. Our study included 60 papers describing 81 patients fulfilling the eligibility criteria. The treatment with interleukin inhibitors resulted in 70% (95% CI 59-80%) response and 57% (95% CI 45-68%) complete response rates, and few (4%) mild adverse events, hence supporting the off-label use for the treatment of recalcitrant PG in adults. The response and complete response rates were 59% (17/29) and 38% (11/29) for anakinra, 64% (7/11) and 55% (6/11) for canakinumab, and 79% (27/34) and 71% (24/34) for ustekinumab, respectively. Limitations include publication bias that might have overestimated the efficacy as successful cases responding to treatment are more likely to be reported than nonresponding cases. Additionally, the heterogeneity of the treatment groups does not allow conclusions of superiority or inferiority of the different interleukin inhibitors to be drawn. Further studies are needed to investigate the efficacy of the different interleukin inhibitors and to investigate the importance of underlying disease for treatment response.

Rare Case of Pyoderma Gangrenosum in the Setting of PAPA Syndrome in a 12-Year-Old Child

We report on a 12-year-old boy who presented with an intermittently painful wound present for months without any tendency to heal after a slackline accident two years ago. A biopsy of the ulcer margin revealed epithelial hyperplasia, marked fibrosis, and vascular proliferation without evidence of vasculitis. Pretibial findings on the right side were a 3.8 ×  3.1 cm fibrin-covered, flat ulcer with slight reddening of the surrounding area. Other findings were unremarkable with hypermobility of the wrists and finger joints. Local therapy with a foam dressing, topical steroid in the wound margin, and class II compression stockings showed no effect. The pediatric rheumatologist evaluated the ulcer with a camptodactyly of digit 5, subluxation of the wrists on both sides, and symmetric ulnar deviation. Elevated S100 as an isolated autoimmune phenomenon or concomitant with systemic autoimmune disease or autoinflammation (eg, Pyogenic sterile arthritis, pyoderma gangrenosum, and acne syndrome) was also observed. The therapy with oral steroids, initially 30 mg/day and gradual reduction in the course, only achieved a tissue bridge's formation with the same size extension of the ulcer. Unfortunately, the patient spontaneously developed a second ulcer on the left lateral malleolus, which is why the therapy was changed to dapsone 50 mg/day and tacrolimus in the wound margin after nine weeks. In the absence of success, further treatment with ciclosporin or tumor necrosis factor-alpha antibody therapy is planned in interdisciplinary cooperation.

Pyogenic arthritis, pyoderma gangrenosum, and acne syndrome in a Chinese family: A case report and review of literature

BACKGROUND

Pyogenic arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome is a rare autosomal dominant genetic disease characterized by severe autoimmune inflammation, caused by mutations in the PSTPIP1 gene. Due to PAPA heterogeneous clinical manifestation, misdiagnosis or delayed diagnoses are difficult to avoid. With the use of whole-exome sequencing, we identified a missense mutation in the PSTPIP1 gene in a Chinese family. To the best of our knowledge, this is the first case of PAPA reported in China.

CASE SUMMARY

A 9-year-old boy suffered from recurrent aseptic pyogenic arthritis triggered by minor trauma or few obvious predisposing causes for more than 3 years. Pyogenic arthritis occurred every 3-5 mo, affecting his knees, elbows, and ankle joints. Treatments, such as glucocorticoids, antibiotics, even surgeries could alleviate joints pain and swelling to some extent but could not inhibit the recurrence of arthritis. Similar symptoms were present in his younger brother but not in his parents. According to the whole-exome sequencing, a missense mutation in exon 11 of the PSTPIP1 gene (c.748G>C; p.E250Q) was detected in the boy, his younger brother and his father. Taking into account the similar phenotypic features with PAPA syndrome reported previously, we confirmed a diagnosis of PAPA syndrome for the family.

CONCLUSION

In this case, a missense mutation (c.748G>C; p.E250Q) in PSTPIP1 gene was identified in a Chinese family with PAPA syndrome. Previous studies emphasize the fact that PAPA syndrome is hard to diagnose just through the clinical manifestations owing to its heterogeneous expression. Genetic testing is an effectual auxiliary diagnostic method, especially in the early stages of pyogenic arthritis. Only if we have a deep understanding and rich experience of this rare disease can we make a prompt diagnosis, develop the best clinical treatment plan, and give good fertility guidance.

Chronic Nonbacterial Osteomyelitis in Children

Chronic nonbacterial osteomyelitis (CNO) is an auto-inflammatory bone disorder with a wide spectrum of clinical manifestations, from unifocal to multifocal lesions. When it manifests with multifocal lesions, it is also referred to as chronic recurrent multifocal osteomyelitis (CRMO). CNO/CRMO can affect all age groups, with the pediatric population being the most common. Patients may present with systemic inflammation, but there is no pathognomonic laboratory finding. Magnetic resonance imaging (MRI) is the gold standard radiological tool for diagnosis. In the absence of validated diagnostic criteria, CNO/CRMO remains an exclusion diagnosis. Bone biopsy does not show a specific disease pattern, but it may be necessary in unifocal or atypical cases to differentiate it from malignancy or infection. First-line treatments are non-steroidal anti-inflammatory drugs (NSAIDs), while bisphosphonates or TNF-α blockers can be used in refractory cases. The disease course is unpredictable, and uncontrolled lesions can complicate with bone fractures and deformations, underlying the importance of long-term follow-up in these patients.

PAMI syndrome: A rare cause that can be easily misdiagnosed

PSTPIP1-associated myeloid-related proteinemia inflammatory (PAMI) syndrome caused by mutations in PSTPIP1 is a rare inflammatory disorder that can be easily misdiagnosed. It is characterized by anemia, arthritis, cutaneous inflammation, recurrent infections, growth failure, hepatosplenomegaly, lymphadenopathy, hyperzincemia/hypercalprotectinemia, neutropenia, thrombocytopenia, and elevated inflammatory indicators. This study describes the cases of two pediatric female patients with long-standing recurrent arthralgia in different parts of the extremities and severe anemia, respectively, who were misdiagnosed and treated for aseptic necrosis of the femoral head and severe autoimmune hemolytic anemia, respectively. High-throughput sequencing analysis revealed a de novo heterozygous missense mutation (c.748G > A, p. Glu250Lys) in exon 11 of PSTPIP1 (NM_003978.5) in both patients, which supported a diagnosis of PAMI. The patients were treated with prednisone and etanercept, which improved their symptoms, but neutropenia remained unchanged. These cases highlight the importance of genetic assessment for the accurate diagnosis of PAMI and to ensure adequate and timely treatment of these patients.

Molecular mechanisms of phenotypic variability in monogenic autoinflammatory diseases

Monogenic autoinflammatory diseases are a group of rheumatologic disorders caused by dysregulation in the innate immune system. The molecular mechanisms of these disorders are linked to defects in inflammasome-mediated, NF-κB-mediated or interferon-mediated inflammatory signalling pathways, cytokine receptors, the actin cytoskeleton, proteasome complexes and various enzymes. As with other human disorders, disease-causing variants in a single gene can present with variable expressivity and incomplete penetrance. In some cases, pathogenic variants in the same gene can be inherited either in a recessive or dominant manner and can cause distinct and seemingly unrelated phenotypes, although they have a unifying biochemical mechanism. With an enhanced understanding of protein structure and functionality of protein domains, genotype-phenotype correlations are beginning to be unravelled. Many of the mutated proteins are primarily expressed in haematopoietic cells, and their malfunction leads to systemic inflammation. Disease presentation is also defined by a specific effect of the mutant protein in a particular cell type and, therefore, the resulting phenotype might be more deleterious in one tissue than in another. Many patients present with the expanded immunological disease continuum that includes autoinflammation, immunodeficiency, autoimmunity and atopy, which necessitate genetic testing.

Autoinflammatory syndromes

Autoinflammatory syndromes are a steadily growing group of inflammatory diseases caused by abnormal regulations of the innate immune system. The clinical presentation is multifaceted, but recurrent fever, skin involvement, joint inflammation and other systemic symptoms of inflammation are characteristic. In contrast to classic autoimmune diseases, autoantibodies or specific T cells are not involved in the pathogenesis. In fact, innate immunity plays the most important role in autoinflammation. While activation of the innate immune system is usually self-limiting in healthy individuals, mutations and dysregulation can lead to chronic and excessive activation of innate immune responses and to the development of autoinflammatory diseases.

The neutrophil inflammasome

Since inflammasomes were discovered in the early 21st century, knowledge about their biology has multiplied exponentially. These cytosolic multiprotein complexes alert the immune system about the presence of infection or tissue damage, and regulate the subsequent inflammatory responses. As inflammasome dysregulation is increasingly associated with numerous autoinflammatory disorders, there is an urgent need for further research into the inflammasome's involvement in the pathogenesis of such diseases in order to identify novel therapeutic targets and treatments. The zebrafish has become a widely used animal model to study human diseases in recent years, and has already provided relevant findings in the field of inflammasome biology including the identification of new components and pathways. We provide a detailed analysis of current knowledge on neutrophil inflammasome biology and compare its features with those of the better known macrophage inflammasome, focusing on its contribution to innate immunity and its relevance for human health. Importantly, a large body of evidence points to a link between neutrophil inflammasome dysfunction and many neutrophil-mediated human diseases, but the real contribution of the neutrophil inflammasome to the pathogenesis of these disorders is largely unknown. Although neutrophils have remained in the shadow of macrophages and monocytes in the field of inflammasome research since the discovery of these multiprotein platforms, recent studies strongly suggest that the importance of the neutrophil inflammasome has been underestimated.

Rare cases of PAMI syndrome in both father and son with the same missense mutation in PSTPIP1 gene and literature review

PSTPIP1-associated myeloid-related proteinaemia inflammatory (PAMI) syndrome has been described as a rare and distinct clinical phenotype of PSTPIP1-associated inflammatory diseases. We report PSTPIP1 mutation in both father and son who have leukopenia and acne-like lesions. Through whole-exome sequencing on blood DNA, it is found a heterozygous mutation of PSTPIP1 gene c.748G>A on the father and son. The diagnosis of PAMI is made based on DNA sequencing results and clinical characteristics of typical lesions, leukopenia, and the markedly increased serum S100A8/A9 (calprotectin).

Incorporating joint pain screening into the pediatric dermatologic examination

BACKGROUND/OBJECTIVES

Joint manifestations are a feature of many pediatric skin disorders, among them psoriasis, autoimmune and autoinflammatory diseases, hypermobility disorders, and as an adverse effect of certain medications. Identifying joint disease early is important for intervention and prevention of chronic damage. However, pediatric musculoskeletal complaints are common and determining whether symptoms warrant a rheumatology referral for arthritis can be challenging.

METHODS

Pediatric dermatologists were surveyed for their comfort in screening for joint disease. Through literature review and interviews with three pediatric rheumatologists, key joints involved in disorders with skin manifestations and arthritis were identified and the essential evaluations were determined.

RESULTS

Of 100 surveyed practicing board-certified pediatric dermatologists, 79% did not feel confident in their ability to perform a joint-focused physical examination, a key step in screening for joint disease. A rapid joint examination technique (R-JET) was developed, along with an accompanying three-question survey and body diagram for patient self-report of symptoms. A video demonstration of the R-JET was created as a teaching tool.

CONCLUSIONS

Teaching and incorporation of a rapid screening examination for arthritis by pediatric dermatologists has the potential to identify pediatric arthritis earlier, facilitate referral, and reduce the risk of progressive joint disease. These instruments can easily be incorporated into a pediatric dermatology office visit.

Phenotypic Associations of PSTPIP1 Sequence Variants in PSTPIP1-Associated Autoinflammatory Diseases

Pathogenic variants in the PSTPIP1 gene cause pyogenic sterile arthritis, pyoderma gangrenosum, and acne (PAPA) syndrome. They were also identified in a broad spectrum of phenotypes. As their interpretation is sometimes challenging, we discuss the genotype-phenotype association in PSTPIP1-associated autoinflammatory diseases (PAIDs) in light of a recent consensus classification of variant pathogenicity. Only 7 of 39 (18%) of the PSTPIP1 variants found in all reported cases and our national reference center (161 patients [114 probands]) were pathogenic. They were clearly associated with PAPA and PSTPIP1-associated myeloid-related proteinemia inflammatory syndrome (PAMI), reflecting a variable clinical expression of PAIDs.

Ancient friends, revisited: Systematic review and case report of pyoderma gangrenosum-associated autoinflammatory syndromes

In the last decade, new scientific findings significantly improved our understanding of the molecular pathogenesis of autoinflammation and have resulted in the identification and definition of several pyoderma gangrenosum-associated autoinflammatory syndromes (PGAAIS) as new and distinct clinical entities. These different clinical entities include PAPA (pyogenic arthritis, pyoderma gangrenosum and acne conglobata), PASH (pyoderma gangrenosum, acne and suppurative hidradenitis), PAPASH (pyoderma gangrenosum, acne, suppurative hidradenitis and pyogenic arthritis), PsAPASH (pyoderma gangrenosum, acne, suppurative hidradenitis and psoriatic arthritis), PASS (pyoderma gangrenosum, acne conglobata, suppurative hidradenitis, and axial spondyloarthritis) and PAC (pyoderma gangrenosum, acne and ulcerative colitis), which can be distinguished by their clinical presentation and the presence or absence of mutations in several genes, such as the genes encoding proline-serine-threonine phosphatase-interacting protein 1 (PSTPIP1), nicastrin (NCSTN), Mediterranean fever (MEFV) and nucleotide-binding oligomerization domain-containing protein (NOD). In this systematic review, we summarize the present knowledge of this rapidly developing hot topic and provide a guide to enable the easy diagnosis of these syndromes in everyday clinical practice. Moreover, we report a rare case of PASS syndrome demonstrating successful treatment with adalimumab and another case of a previously unreported combination of symptoms, including psoriatic arthritis, pyoderma gangrenosum, suppurative hidradenitis and Crohn’s disease (newly coined PsAPSC), as examples. Because of the identification of similar genetic and pathogenic mechanisms of PGAAIS, we think the wide variety of seemingly different syndromes may represent distinct phenotypes of one disease.

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New scientific findings improved the understanding of the molecular pathogenesis of autoinflammation.

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There is a similar genetic background and clinical findings of PGAAIS.

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Because of the similar genetic and pathogenic mechanisms of PGAAIS may represent distinct phenotypes of one disease.

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We present a 4-sep guide to enable the easy diagnosis of theses disease in clinical practice.

A Unified Concept of Acne in the PAPA Spectrum Disorders

BACKGROUND

Acne is a common condition. Sometimes acne or acne-like features are a part of autoinflammatory diseases such as PAPA spectrum disorders. Our objective wasto determine whether acne in PAPA spectrum disorders has specific phenotypic traits.

SUMMARY

This is aliterature review on reported cases of patients with PAPA, PAMI, PASH, PAPASH, PsAPASH, PAC or PASS syndrome. Acne was classified into four categories: moderate, severe, nodulocystic, acne fulminans.One hundred patients were included. Age of onset of acne and topography were the same as in acne vulgaris. Acne's phenotype was at least severe (including acne fulminans, nodulocystic and severe) in 83% of cases. Genetic mutations or variants with potential pathological significance were reported in 49 patients. The addition of isotretinoin to biotherapies was required to control acne in several patients.

PAPA spectrum disorders

Pyogenic arthritis, pyoderma gangrenosum (PG) and acne (PAPA) syndrome is an autosomal dominant autoinflammatory syndrome due to mutations in proline-serine-threonine phosphatase interacting protein 1 (PSTPIP1) gene and presenting with cutaneous and articular manifestations. Other autoinflammatory syndromes caused by mutations in PSTPIP1 gene or characterized by clinical findings overlapping with those found in PAPA syndrome have been recently included in the group of PAPA spectrum disorders. These disorders are PASH (PG, acne and hidradenitis suppurativa [HS]), PAPASH (PASH associated with pyogenic sterile arthritis), PsAPASH (PASH combined with psoriatic arthritis [PsA], PASS (PG, acne, ankylosing spondylitis, with or without HS), PAC (PG, acne and ulcerative colitis [UC]) and PAMI syndrome (PSTPIP1-associated myeloid-related-proteinemia inflammatory syndrome). Except for PAPA and PAMI, no specific pathogenetic mutations have been identified in these syndromes. Dermatologists should be aware that PG, acne and HS may represent cutaneous signs hiding the presence of these rare entities. Systemic corticosteroids, a number of immunosuppressants and biologics, such as interleukin (IL)-1 antagonists and tumour necrosis factor (TNF) α inhibitors, are nowadays therapy for these diseases. A pathogenesis-driven treatment is the near future in the management of these conditions.

A child with recurrent pyogenic arthritis with the PSTPIP1 mutation

Pyogenic arthritis, pyoderma gangrenosum, and acne syndrome is a rare disease, linked to an auto-inflammatory pathway. We report a 7-year-old boy with recurrent suppurative knee arthritis without signs of suppurative skin infection or ulcer; his younger brother had the same symptom. Genetic testing indicated the presence of proline-serine-threonine phosphatase interacting protein 1 gene mutation in both boys. Our patient’s grandfather had a history of recurrent pyoderma, and his father though a genetic carrier had no symptoms. Interestingly, our patient displayed markedly high levels of interleukin-6, while interleukin-1 and other cytokines were not elevated. These lab findings led to the treatment of pyogenic arthritis, pyoderma gangrenosum, and acne syndrome with tocilizumab. Previously reported cases of similar phenotypes of the syndrome have not presented in this fashion, nor have there been reported cases of pyogenic arthritis, pyoderma gangrenosum, and acne syndrome with a positive family history and an elevation in interleukin-6. The mutation site of proline-serine-threonine phosphatase interacting protein 1 in this incomplete pyogenic arthritis, pyoderma gangrenosum, and acne syndrome has not been reported before. It is possible that there are other pathogenic ways to trigger these auto-inflammatory disorders. Tocilizumab, which specifically targets interleukin-6, was effective in this case.

Pyoderma gangrenosum: From historical perspectives to emerging investigations

Pyoderma gangrenosum (PG) is a rare disease of unknown aetiology, first described over a century ago. Initially thought to have an infectious cause, and now primarily considered an autoinflammatory condition, PG continues to be poorly understood, commonly misdiagnosed, and difficult to treat. In this review, we discuss the journey of our understanding of PG to date, including first descriptions, challenges with diagnosis, presumed pathogenesis, and treatments used. We highlight major historical landmarks and their importance, explain the rationale behind current investigations, note outstanding gaps in knowledge, and explore the future directions of PG research. We summarise what we have known, what we are working on knowing, and what we have yet to explore about PG, illustrating overall trends to invigorate future research.

Off-Label studies on anakinra in dermatology: a review

Purpose: Anakinra (Kineret^®) is an interleukin-1 receptor antagonist (IL-1Ra) FDA approved for use in rheumatoid arthritis and in neonatal-onset multisystem inflammatory disease (NOMID). It has been used off-label for a variety of dermatologic conditions. A review of the available studies and cases of these off-label uses would be valuable to the dermatologist considering alternative treatments for these oftentimes poorly studied conditions.Materials and methods: The PubMed/MEDLINE, EMBASE, Scopus, and ClinicalTrials.gov databases were searched with the term 'anakinra.' Results were manually screened to identify published data on off-label uses of anakinra in dermatologic conditions and systemic conditions with prominent dermatologic manifestations.Results: Anakinra appears to show efficacy for numerous dermatologic conditions, with the strongest evidence for hidradenitis suppurativa, Bechet's disease, Muckle-Wells syndrome, and SAPHO syndrome. Case reports and case series data are available for numerous other dermatologic conditions.Conclusion: Anakinra is a potential option for patients with certain difficult-to-treat dermatologic diseases, given its relatively benign adverse effect profile and its effectiveness in a wide array of conditions. Overall, anakinra appears to be a promising option in the treatment of numerous dermatologic inflammatory conditions refractory to first line therapies, but further and higher-quality data is needed to clarify its therapeutic role.

Autoinflammatory diseases in childhood, part 1: monogenic syndromes

Autoinflammatory diseases constitute a family of disorders defined by aberrant stimulation of inflammatory pathways without involving antigen-directed autoimmunity. They may be divided into monogenic and polygenic types. Monogenic autoinflammatory syndromes are those with identified genetic mutations, such as familial Mediterranean fever, tumor necrosis factor receptor-associated periodic fever syndrome (TRAPS), mevalonate kinase deficiency or hyperimmunoglobulin D syndrome, cryopyrin-associated periodic fever syndromes (CAPS), pyogenic arthritis pyoderma gangrenosum and acne (PAPA) syndrome, interleukin-10 and interleukin-10 receptor deficiencies, adenosine deaminase 2 deficiency and pediatric sarcoidosis. Those without an identified genetic mutation are known as polygenic and include systemic-onset juvenile idiopathic arthritis, idiopathic recurrent acute pericarditis, Behçet syndrome, chronic recurrent multifocal osteomyelitis and inflammatory bowel disease among others. Autoinflammatory disorders are defined by repeating episodes or persistent fever, rash, serositis, lymphadenopathy, arthritis and increased acute phase reactants, and thus may mimic infections clinically. Most monogenic autoinflammatory syndromes present in childhood. However, because of their infrequency, diverse and nonspecific presentation, and the relatively new genetic recognition, diagnosis is usually delayed. In this article, which is Part 1 of a two-part series, the authors update monogenic autoinflammatory diseases in children with special emphasis on imaging features that may help establish the correct diagnosis.

Dermatologic and Dermatopathologic Features of Monogenic Autoinflammatory Diseases

Autoinflammatory diseases include disorders with a monogenic cause and also complex conditions associated to polygenic or multifactorial factors. An increased number of both monogenic and polygenic autoinflammatory conditions have been identified during the last years. Although skin manifestations are often predominant in monogenic autoinflammatory diseases, clinical and histopathological information regarding their dermatological involvement is still scarce. Monogenic autoinflammatory diseases with cutaneous expression can be classified based on the predominant lesion: (1) maculopapular rashes or inflammatory plaques; (2) urticarial rashes; (3) pustular, pyogenic or neutrophilic dermatosis-like rashes; (4) panniculitis or subcutaneous nodules; (5) vasculitis or vasculopathy; (6) hyperkeratotic lesions; (7) hyperpigmented lesions; (8) bullous lesions; and (9) aphthous lesions. By using this classification, this review intends to provide clinical and histopathological knowledge about cutaneous involvement in monogenic autoinflammatory diseases.

[PAPA syndrome with Crohn's disease and primary sclerosing cholangitis/autoimmune hepatitis overlap syndrome]

BACKGROUND

The PAPA syndrome, an acronym for pyogenic sterile arthritis, pyoderma gangraenosum and acne, is an autosomal dominant hereditary disease which is caused by a mutation in the PSTPIP1 ("proline-serine-threonine phosphatase interacting protein 1") gene located on chromosome 15 and encodes the proline-serine-threonine phosphatase-interacting protein 1. An association with Crohn's disease (CD), autoimmune diseases of the liver and PAPA syndrome has not yet been reported in the literature.

OBJECTIVE

To thoroughly investigate a family with three affected members (mother and 2 children) with newly diagnosed PAPA syndrome and intestinal and hepatobiliary symptoms.

MATERIAL AND METHODS

We performed an in-depth phenotyping, dermatologic, radiologic, rheumatologic, gastroenterologic, histologic and genetic analysis in this family.

RESULTS

All three family members could be newly diagnosed as suffering from PAPA syndrome and carried the known disease-causing mutation c.688G > A (p.Ala230Thr) in the PSTPIP1 gene. The younger son suffered from CD in addition to PAPA syndrome. The mother additionally suffered from ulcerative colitis (UC) and an overlap syndrome between autoimmune hepatitis (AIH) and primary sclerosing cholangitis (PSC). A mutation in in the NOD2 ("nucleotide binding oligomerization domain containing protein 2") gene could not be detected in any of the three persons affected.

CONCLUSION

We extended the symptoms of PAPA syndrome to CD and autoimmune liver disease. These different disease entities might share a similar pathogenetic mechanism or even represent a new syndrome. This can be clarified in the future by screening patients with PAPA syndrome for intestinal and also hepatobiliary diseases.

Autoinflammatory Disorders: A Review and Update on Pathogenesis and Treatment

The autoinflammatory diseases comprise a broad spectrum of disorders characterized by unchecked activation of the innate immune system. Whereas aberrations in adaptive immunity have long been identified in 'autoimmune' disorders, the concept of 'autoinflammation' emerged relatively recently, first describing a group of clinical disorders characterized by spontaneous episodes of systemic inflammation without manifestations typical of autoimmune disorders. Improved knowledge of innate immune mechanisms, coupled with remarkable progress in genomics and an expanding number of clinical cases, has since led to an increasing number of disorders classified as autoinflammatory or containing an autoinflammatory component. Biologic therapies targeting specific components of the innate immune system have provided immense clinical benefit, and have further elucidated the role of innate immunity in autoinflammatory disorders. This article reviews the basic mechanisms of autoinflammation, followed by an update on the pathophysiology and treatment of the monogenic and multifactorial autoinflammatory diseases, and the common dermatologic conditions in which autoinflammation plays a major role.

Mechanisms of Inflammation in Neutrophil-Mediated Skin Diseases

Neutrophil-mediated skin diseases, originally named neutrophilic dermatoses (NDs), are a group of conditions due to an altered neutrophil recruitment and activation, characterized by polymorphic cutaneous manifestations with possible internal organ involvement. Although a number of diseases are included in this setting, the two prototypic forms are pyoderma gangrenosum (PG) and Sweet's syndrome (SS) which usually present with skin ulcers and plaque-type lesions, respectively. They have central features significantly overlapping with autoinflammatory conditions which manifest as repeated episodes of tissue inflammation. However, in contrast to appropriate inflammatory responses to insults or to autoimmune disease, there is an absence of identifiable pathogens, autoantibodies, or autoreactive lymphocytes. The recognition of monogenic autoinflammatory diseases which can present with NDs has led to study several genes involved in autoinflammation in NDs. Based on discovering of a number of mutations involving different autoinflammatory genes, neutrophil-mediated skin diseases are nowadays regarded as a spectrum of polygenic autoinflammatory conditions. Although disease mechanisms have not yet been completely elucidated, NDs are recognized as diseases involving dysfunctional cellular signaling mediated by pathways mainly related to inflammasome and IL-1 with the contributory role of IL-17 and other effector molecules. The precise elucidation of the above-mentioned pathologic mechanisms may pave the way to tailored treatments for patients with different neutrophil-mediated skin diseases.

Imaging findings of sterile pyogenic arthritis, pyoderma gangrenosum and acne (PAPA) syndrome: differential diagnosis and review of the literature

Pyogenic arthritis, pyoderma gangrenosum and acne (PAPA) syndrome is a rare autosomal-dominant autoinflammatory disease of incomplete penetrance and variable expression. PAPA syndrome is the result of a mutation in the proline serine threonine phosphatase-interacting protein 1 (PSTPIP1/CD2BP1) gene located on chromosome 15, which results in an abnormal overproduction of the pro-inflammatory cytokine interleukin-1β (IL-1). This syndrome clinically manifests as early onset of recurrent episodes of acute aseptic inflammation of the joints, generally occurring in the first two decades of life, followed by manifestation of characteristic skin lesions in the third decade, after an obvious decline in the joint symptoms. Although uncommon, the potential clinical implications of PAPA syndrome warrant an appropriate diagnosis in a timely fashion.

The classification, genetic diagnosis and modelling of monogenic autoinflammatory disorders

Monogenic autoinflammatory disorders are an increasingly heterogeneous group of conditions characterised by innate immune dysregulation. Improved genetic sequencing in recent years has led not only to the discovery of a plethora of conditions considered to be 'autoinflammatory', but also the broadening of the clinical and immunological phenotypic spectra seen in these disorders. This review outlines the classification strategies that have been employed for monogenic autoinflammatory disorders to date, including the primary innate immune pathway or the dominant cytokine implicated in disease pathogenesis, and highlights some of the advantages of these models. Furthermore, the use of the term 'autoinflammatory' is discussed in relation to disorders that cross the innate and adaptive immune divide. The utilisation of next-generation sequencing (NGS) in this population is examined, as are potential in vivo and in vitro methods of modelling to determine pathogenicity of novel genetic findings. Finally, areas where our understanding can be improved are highlighted, such as phenotypic variability and genotype-phenotype correlations, with the aim of identifying areas of future research.

Dysregulated neutrophil responses and neutrophil extracellular trap formation and degradation in PAPA syndrome

OBJECTIVES

Pyogenic arthritis, pyoderma gangrenosum and acne (PAPA) syndrome is characterised by flares of sterile arthritis with neutrophil infiltrate and the overproduction of interleukin (IL)-1β. The purpose of this study was to elucidate the potential role of neutrophil subsets and neutrophil extracellular traps (NET) in the pathogenesis of PAPA.

METHODS

Neutrophils and low-density granulocytes (LDG) were quantified by flow cytometry. Circulating NETs were measured by ELISA and PAPA serum was tested for the ability to degrade NETs. The capacity of NETs from PAPA neutrophils to activate macrophages was assessed. Skin biopsies were analysed for NETs and neutrophil gene signatures.

RESULTS

Circulating LDGs are elevated in PAPA subjects. PAPA neutrophils and LDGs display enhanced NET formation compared with control neutrophils. PAPA sera exhibit impaired NET degradation and this is corrected with exogenous DNase1. Recombinant human IL-1β induces NET formation in PAPA neutrophils but not healthy control neutrophils. NET formation in healthy control neutrophils is induced by PAPA serum and this effect is inhibited by the IL-1 receptor antagonist, anakinra. NETs from PAPA neutrophils and LDGs stimulate IL-6 release in healthy control macrophages. NETs are detected in skin biopsies of patients with PAPA syndrome in association with increased tissue IL-1β, IL-8 and IL-17. Furthermore, LDG gene signatures are detected in PAPA skin.

CONCLUSIONS

PAPA syndrome is characterised by an imbalance of NET formation and degradation that may enhance the half-life of these structures in vivo, promoting inflammation. Anakinra ameliorates NET formation in PAPA and this finding supports a role for IL-1 signalling in exacerbated neutrophil responses in this disease. The study also highlights other inflammatory pathways potentially pathogenic in PAPA, including IL-17 and IL-6, and these results may help guide new therapeutic approaches in this severe and often treatment-refractory condition.

From autoinflammation to autoimmunity: old and recent findings

Autoimmune diseases and autoinflammatory diseases have a number of similar etiopathogenetic and clinical characteristics, including genetic predisposition and recurrent systemic inflammatory flares. The first phase of ADs involves innate immunity: by means of TLRs, autoantigen presentation, B and T cell recruitment and autoantibody synthesis. The second phase involves adaptive immunity, a self-sustaining process in which immune complexes containing nucleic acids and autoantibodies activate self-directed inflammation. The link between autoimmunity and autoinflammation is IL-1ß, which is crucial in connecting the innate immune response due to NLR activation and the adaptive immune responses of T and B cells. In conclusion, although ADs are still considered adaptive immunity-mediated disorders, there is increasing evidence that innate immunity and inflammasomes are also involved. The aim of this review is to highlight the link between the innate and adaptive immune mechanisms involved in autoimmune diseases.

A clinical update on inflammasomopathies

Inflammasomes are important elements of the innate immune defense. The most common autoinflammatory syndromes, as well a number of rare ones, are due to hereditary defects in the inflammasomes, hence are called inflammasomopathies. The recent clinical advances in these diseases will be reviewed, with special emphasis on reflecting the international collaborative work in the field. Recent recommendations for familial Mediterranean fever, cryopyrin-associated periodic syndromes and hyper-IgD syndrome/mevalonate kinase deficiency will be presented and diagnostics tests, treatment alternatives and follow-up recommendations will be summarized. The other rare inflammasomopathies will be briefly discussed based on clinical features; these diseases are pyogenic arthritis, pyoderma gangrenosum and acne, NLRC4-related macrophage-activation syndrome of enterocolitis, mutations in NLRP12 that cause hereditary periodic fever syndromes (familial cold inflammatory syndrome 2) and NLRP1-associated autoinflammation with arthritis and dyskeratosis.