OTULIN-related conditions: Report of a new case and review of the literature using GenIA.

OTULIN encodes an eponymous linear deubiquitinase (DUB) essential for controlling inflammation as a negative regulator of the canonical NF-κB signaling pathway via the regulation of M1-Ub dynamics. Biallelic loss-of-function (LOF) mutations in OTULIN cause an autosomal recessive condition named Otulin-Related Autoinflammatory Syndrome (ORAS), also known as Otulipenia or AutoInflammation, Panniculitis, and Dermatosis Syndrome (AIPDS). Monoallelic OTULIN LOF, also known as OTULIN Haploinsufficiency (OHI) or Immunodeficiency 107 (IMD107), has been linked to an incompletely penetrant, dominantly inherited susceptibility to invasive Staphylococcal infections. At the same time, a recent novel ORAS-like inflammatory syndrome was described in association with a heterozygous missense mutation that appears to exert dominant negative (DN) effects. In this manuscript, we report the identification of a novel homozygous missense mutation, c.595 T > A; p.(Trp199Arg), in a Moroccan infant with an ORAS phenotype and provide experimental evidence for its pathogenicity. We go on to systematically review the literature for OTULIN-associated conditions by using the GenIA database (www.geniadb.net) to collect, extract and harmonize all clinical, laboratory and functional data for published patients and variants. Our comprehensive synthesis of genotypic, phenotypic, and mechanistic data enables a more in-depth view of the diverse mechanisms and pathways by which the OTULIN pathogenic variants may lead to human immune disease. This review may help variant classification activities and inform future variant evaluation, as well as the development of diagnostic and management guidelines. It also identifies current knowledge gaps and raises additional questions warranting future investigation.

Interrupting an IFN-γ-dependent feedback loop in the syndrome of pyogenic arthritis with pyoderma gangrenosum and acne.

OBJECTIVES: To study the molecular pathogenesis of PAPA (pyogenic arthritis, pyoderma gangrenosum and acne) syndrome, a debilitating hereditary autoinflammatory disease caused by dominant mutation in PSTPIP1. METHODS: Gene knock-out and knock-in mice were generated to develop an animal model. THP1 and retrovirally transduced U937 human myeloid leukaemia cell lines, peripheral blood mononuclear cells, small interfering RNA (siRNA) knock-down, site-directed mutagenesis, cytokine immunoassays, coimmunoprecipitation and immunoblotting were used to study inflammasome activation. Cytokine levels in the skin were evaluated by immunohistochemistry. Responsiveness to Janus kinase (JAK) inhibitors was evaluated ex vivo with peripheral blood mononuclear cells and in vivo in five treatment-refractory PAPA patients. RESULTS: The knock-in mouse model of PAPA did not recapitulate the human disease. In a human myeloid cell line model, PAPA-associated PSTPIP1 mutations activated the pyrin inflammasome, but not the NLRP3, NLRC4 or AIM2 inflammasomes. Pyrin inflammasome activation was independent of the canonical pathway of pyrin serine dephosphorylation and was blocked by the p.W232A PSTPIP1 mutation, which disrupts pyrin-PSTPIP1 interaction. IFN-γ priming of monocytes from PAPA patients led to IL-18 release in a pyrin-dependent manner. IFN-γ was abundant in the inflamed dermis of PAPA patients, but not patients with idiopathic pyoderma gangrenosum. Ex vivo JAK inhibitor treatment attenuated IFN-γ-mediated pyrin induction and IL-18 release. In 5/5 PAPA patients, the addition of JAK inhibitor therapy to IL-1 inhibition was associated with clinical improvement. CONCLUSION: PAPA-associated PSTPIP1 mutations trigger a pyrin-IL-18-IFN-γ positive feedback loop that drives PAPA disease activity and is a target for JAK inhibition.

Genetic Approaches to Study Rheumatic Diseases and Its Implications in Clinical Practice.

Patients with rare and complex rheumatic diseases (RDs) present with immense clinical variability inherent to all immunologic diseases. In addition to systemic and organ-specific inflammation, patients may display features of immunodeficiency or allergy, which may represent major diagnostic and therapeutic challenges. The person's genetic architecture has been a well-established risk factor for patients with RDs, albeit to variable degrees. Patients with early-onset diseases and/or positive family history (FH) have a strong genetic component, whereas patients with late-onset RDs demonstrate a more complex interplay of genetic and environmental risk factors. Overall, the genetic studies in patients with RDs have been instrumental to our understanding of innate and adaptive immunity in human health and disease. The elucidation of the molecular causes underlying rare diseases has played a major role in the identification of genes that are critical in the regulation of inflammatory responses. In addition, studies of patients with rare disorders may help determine the mechanisms of more complex autoimmune diseases by identifying variants with small effect sizes in the same genes. In contrast, studies of patients with common RDs are conducted in cohorts of patients with well-established phenotypes and ancestry-matched controls, and they aim to discover disease-related pathways that can inform the development of novel targeted therapies. Knowing the genetic cause of a disease has helped patients and families understand the disease progression and outcome. Here, we discuss the current understanding of genetic heritability and challenges in the diagnosis of RDs in patients and how this field may develop in the future.

The past 25 years in paediatric rheumatology: insights from monogenic diseases.

The past 25 years have seen major novel developments in the field of paediatric rheumatology. The concept of autoinflammation was introduced to this field, and medicine more broadly, with studies of familial Mediterranean fever, the most common autoinflammatory disease globally. New data on the positive evolutionary selection of familial Mediterranean fever-associated genetic variants might be pertinent to mild gain-of-function variants reported in other disease-associated genes. Genetic studies have unveiled the complexity of human heritability to inflammation and flourishing data from rare monogenic disorders have contributed to a better understanding of general disease mechanisms in paediatric rheumatic conditions. Beyond genomics, the application of other 'omics' technologies, including transcriptomics, proteomics and metabolomics, has generated an enormous dataset that can be applied to the development of new therapies and in the practice of precision medicine. Novel biomarkers for monitoring disease activity and progression have also emerged. A surge in the development of targeted biologic therapies has led to durable remission and improved prognosis for many diseases that in the past caused major complications. Last but not least, the COVID-19 pandemic has affected paediatric rheumatology practice and has sparked new investigations into the link between viral infections and unregulated inflammatory responses in children.

Genetically transitional disease: conceptual understanding and applicability to rheumatic disease.

In genomic medicine, the concept of genetically transitional disease (GTD) refers to cases in which gene mutation is necessary but not sufficient to cause disease. In this Perspective, we apply this novel concept to rheumatic diseases, which have been linked to hundreds of genetic variants via association studies. These variants are in the 'grey zone' between monogenic variants with large effect sizes and common susceptibility alleles with small effect sizes. Among genes associated with rare autoinflammatory diseases, many low-frequency and/or low-penetrance variants are known to increase susceptibility to systemic inflammation. In autoimmune diseases, hundreds of HLA and non-HLA genetic variants have been revealed to be modest- to moderate-risk alleles. These diseases can be reclassified as GTDs. The same concept could apply to many other human diseases. GTD could improve the reporting of genetic testing results, diagnostic yields, genetic counselling and selection of therapy, as well as facilitating research using a novel approach to human genetic diseases.

Combined therapy with IL-1 and JAK inhibitors in a patient with the NLRP1 gene mutation and a complex inflammatory phenotype.

A patient presented with overlapping clinical and laboratory features of 2 rare autoinflammatory diseases, NLRP1-associated autoinflammation with arthritis and dyskeratosis and familial multiple self-healing palmoplantar carcinoma. Her severe inflammatory attack was treated with the IL-1 receptor-α inhibitor anakinra along with the Janus kinase inhibitor ruxolitinib. Three years into the treatment, the patient's inflammatory symptoms are completely in remission.

OTULIN-related conditions: Report of a new case and review of the literature using GenIA.

OTULIN encodes an eponymous linear deubiquitinase (DUB), which through the regulation of M1-Ub dynamics, is essential for controlling inflammation as a negative regulator of the canonical NF-κB signaling pathway. Biallelic loss-of-function (LOF) mutations in OTULIN cause an autosomal recessive condition named Otulin-Related Autoinflammatory Syndrome (ORAS), also known as Otulipenia or AutoInflammation, Panniculitis, and Dermatosis Syndrome (AIPDS). Monoallelic OTULIN LOF, also known as OTULIN Haploinsufficiency (OHI) or Immunodeficiency 107 (IMD107), has been linked to an incompletely penetrant, dominantly inherited susceptibility to invasive Staphylococcal infections. At the same time, a recent novel ORAS-like inflammatory syndrome was described in association with a heterozygous missense mutation that appears to exert dominant negative effects. In this manuscript, we report the identification of a novel homozygous missense mutation, c.595T>A; p.(Trp199Arg), in a Moroccan infant with an ORAS phenotype. We go on to systematically review the literature for OTULIN-related human disease phenotypes by using the GenIA database to collect, extract and harmonize all clinical, laboratory and functional data for published patients and variants. Our comprehensive synthesis of genotypic, phenotypic, and mechanistic data enables a more in-depth view of the diverse mechanisms and pathways by which the OTULIN pathogenic variants may lead to human immune disease. This review may help variant classification activities and the drafting of diagnostic and management guidelines; but it also identifies outstanding knowledge gaps and raises additional questions for future investigation.

Characterization of a Novel Pathogenic PLCG2 Variant Leading to APLAID Syndrome Responsive to a TNF Inhibitor.

OBJECTIVE: Autoinflammation and phospholipase C (PLC) γ2-associated antibody deficiency and immune dysregulation (APLAID) syndrome is an autoinflammatory disease caused by gain-of-function variants in PLCG2. This study investigates the pathogenic mechanism of a novel variant of PLCG2 in a patient with APLAID syndrome. METHODS: Whole-exome sequencing and Sanger sequencing were used to identify the pathogenic variant in the patient. Single-cell RNA sequencing, immunoblotting, luciferase assay, inositol monophosphate enzyme-linked immunosorbent assay, calcium flux assay, quantitative PCR, and immunoprecipitation were used to define inflammatory signatures and evaluate the effects of the PLCG2 variant on protein functionality and immune signaling. RESULTS: We identified a novel de novo variant, PLCG2 p.D993Y, in a patient with colitis, pansinusitis, skin rash, edema, recurrent respiratory infections, B-cell deficiencies, and hypogammaglobulinemia. The single-cell transcriptome revealed exacerbated inflammatory responses in the patient's peripheral blood mononuclear cells. Expression of the D993Y variant in HEK293T, COS-7, and PLCG2 knock-out THP-1 cell lines showed heightened PLCγ2 phosphorylation; elevated inositol-1,4,5-trisphosphate production and intracellular Ca2+ release; and activation of the MAPK, NF-κB, and NFAT signaling pathways compared with control-transfected cells. In vitro experiments indicated that the D993Y variant altered amino acid properties, disrupting the interaction between the catalytic and autoinhibitory domains of PLCγ2, resulting in PLCγ2 autoactivation. CONCLUSION: Our findings demonstrated that the PLCG2 D993Y variant is a gain-of-function mutation via impairing its autoinhibition, activating multiple inflammatory signaling pathways, thus leading to APLAID syndrome. This study further broadens the molecular underpinnings and phenotypic spectrum of PLCγ2-related disorders.

A20 haploinsufficiency disturbs immune homeostasis and drives the transformation of lymphocytes with permissive antigen receptors.

Genetic TNFAIP3 (A20) inactivation is a classical somatic lymphoma lesion and the genomic trait in haploinsufficiency of A20 (HA20). In a cohort of 34 patients with HA20, we show that heterozygous TNFAIP3 loss skews immune repertoires toward lymphocytes with classical self-reactive antigen receptors typically found in B and T cell lymphomas. This skewing was mediated by a feed-forward tumor necrosis factor (TNF)/A20/nuclear factor κB (NF-κB) loop that shaped pre-lymphoma transcriptome signatures in clonally expanded B (CD81, BACH2, and NEAT1) or T (GATA3, TOX, and PDCD1) cells. The skewing was reversed by anti-TNF treatment but could also progress to overt lymphoma. Analysis of conditional TNFAIP3 knock-out mice reproduced the wiring of the TNF/A20/NF-κB signaling axis with permissive antigen receptors and suggested a distinct regulation in B and T cells. Together, patients with the genetic disorder HA20 provide an exceptional window into A20/TNF/NF-κB-mediated control of immune homeostasis and early steps of lymphomagenesis that remain clinically unrecognized.

A unified metric of human immune health.

Immunological health has been challenging to characterize but could be defined as the absence of immune pathology. While shared features of some immune diseases and the concept of immunologic resilience based on age-independent adaptation to antigenic stimulation have been developed, general metrics of immune health and its utility for assessing clinically healthy individuals remain ill defined. Here we integrated transcriptomics, serum protein, peripheral immune cell frequency and clinical data from 228 patients with 22 monogenic conditions impacting key immunological pathways together with 42 age- and sex-matched healthy controls. Despite the high penetrance of monogenic lesions, differences between individuals in diverse immune parameters tended to dominate over those attributable to disease conditions or medication use. Unsupervised or supervised machine learning independently identified a score that distinguished healthy participants from patients with monogenic diseases, thus suggesting a quantitative immune health metric (IHM). In ten independent datasets, the IHM discriminated healthy from polygenic autoimmune and inflammatory disease states, marked aging in clinically healthy individuals, tracked disease activities and treatment responses in both immunological and nonimmunological diseases, and predicted age-dependent antibody responses to immunizations with different vaccines. This discriminatory power goes beyond that of the classical inflammatory biomarkers C-reactive protein and interleukin-6. Thus, deviations from health in diverse conditions, including aging, have shared systemic immune consequences, and we provide a web platform for calculating the IHM for other datasets, which could empower precision medicine.