Mechanisms of vascular inflammation in deficiency of adenosine deaminase 2 (DADA2)

The pathogenesis, clinical presentations and treatment of monogenic systemic vasculitis

Many monogenic autoinflammatory diseases, including DADA2 (deficiency of adenosine deaminase 2), HA20 (haploinsufficiency of A20), SAVI (STING-associated vasculopathy with onset in infancy), COPA syndrome, LAVLI (LYN kinase-associated vasculopathy and liver fibrosis) and VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome, present predominantly with vasculitis and constitute a substantial subgroup of vasculitic conditions associated with a 'probable aetiology'. The spectrum of monogenic vasculitis encompasses all sizes and types of blood vessel, ranging from large vessels to medium-size and small vessels, and from the arterial side to the venous side of the vasculature. Monogenic vasculitis typically starts early in life during infancy or childhood; VEXAS syndrome, which presents in late adulthood, is an exception. The activation of myeloid cells via inflammasome and nuclear factor-κB pathways, type I interferon-enhanced autoimmune mechanisms and/or dysregulated adaptive immune responses have an important role in the development of immune-mediated endothelial dysfunction and vascular damage. Genetic testing is essential for the diagnosis of underlying monogenic autoinflammatory diseases; however, the penetrance of genetic variants can vary. Increased awareness and recognition of distinctive clinical findings could facilitate earlier diagnosis and allow for more-targeted treatments.

Clinical, Immunologic, and Genetic Characteristics in Patients With Syndrome of Undifferentiated Recurrent Fevers

OBJECTIVE

Syndrome of undifferentiated recurrent fevers (SURF) is characterized by recurrent fevers and autoinflammation without a confirmed molecular diagnosis of a hereditary recurrent fever syndrome, and not fulfilling criteria for periodic fever, adenitis, pharyngitis, aphthous stomatitis syndrome (PFAPA). The goal of this study was to characterize clinical features of patients with SURF compared to patients with PFAPA and to analyze their cytokine signature, genetic variations, and responses to treatment.

METHODS

We enrolled 46 patients observed at Cincinnati Children's Hospital Medical Center. Baseline data and inflammatory cytokines were collected at enrollment, and their clinical course was followed. Cytokine analysis was performed using a cytokine multiplex assay. Many patients had specific or whole exome genetic testing.

RESULTS

The prevalence of rash and arthralgias were higher in patients with SURF compared to patients with PFAPA. Pharyngitis and adenopathy were less frequent. A subset of patients with SURF clustered together with elevated proinflammatory cytokines and more frequently required biologic therapy. Focused analysis of whole exome sequencing  data revealed that variants of unknown clinical significance (VUCS) were frequently identified in genes implicated in B cell development, immunodeficiencies, and inflammatory bowel disease risk. Treatments for patients with SURF commonly included on-demand steroids, colchicine, and anti-interleukin-1 therapy.

CONCLUSION

Our findings suggest SURF is a heterogeneous group but has distinct clinical and immunologic features from disorders such as PFAPA. Patients have frequent VUCS, which may have relevance to disease pathogenesis. A subset of patients showed more inflammation and an increased need for biologic therapy. Further research is necessary to define whether there exist distinct SURF endotypes and to better predict treatment outcomes.

Deficiency of adenosine deaminase 2 skews adaptive immune repertoires toward specific sets of T- and B-cell receptors

BACKGROUND

Adenosine deaminase 2 deficiency (DADA2) is a genetic disorder caused by biallelic hypomorphic or loss-of-function mutations in the ADA2 gene, which encodes a protein deaminase regulating extracellular adenosine metabolism. Clinical features encompass inflammatory vasculopathy, early-onset strokes, and a complex presentation involving both immunodeficiency and autoinflammation/autoimmunity.

OBJECTIVE

Our aim was to determine a DADA2-specific adaptive immune architecture.

METHODS

We profiled immunoglobulin levels and peripheral B- and T-cell phenotypes in 47 previously reported and 5 unreported patients with DADA2. Levels of 21 cytokines and chemokines were quantified in patients with or without anti-TNF treatment. To characterize the DADA2 immune architecture, we performed T- and B-cell receptor immunosequencing. We trained a binary LightGBM classifier to distinguish DADA2 T- and B-cell immune repertoires from healthy individuals.

RESULTS

We detected hypogammaglobulinemia in 65% of patients with DADA2 (34 of 52) and cytopenias in 48% (25 of 52). Flow cytometric profiling revealed contraction of B- and T-cell memory compartments. In addition, we observed elevated levels of TNF, IL-8, several interferons, a proliferation-inducing ligand (APRIL), B-cell activating factor (BAFF), and soluble CD40 ligand (sCD40L). High serum levels of TNF, BAFF, and sCD40L persisted under anti-TNF therapy. Next-generation immunosequencing of peripheral lymphocytes showed restricted T-cell receptor repertoires and B cells, which were particularly skewed toward immunoglobulin heavy chain V4-34 rearrangements. With high accuracy, our machine learning algorithm separated individuals with DADA2 from healthy individuals on the basis of immunogenetic parameters regarding B-cell clone fraction, CDR3 length, and selected Kidera factors.

CONCLUSIONS

Our findings underscore the significant influence of ADA2 on the adaptive immune system, which results in a highly specific immunogenetic signature in patients with DADA2.

Novel Link Between Myeloid-Specific Adenosine Deaminase 2 and CXCL10-CXCR3 Axis in Infectious ARDS

Acute respiratory distress syndrome (ARDS) is a severe complication of lung injury characterized by hyperinflammation and fibrosis. Here, we show a significant association between the monocyte-derived enzyme adenosine deaminase 2 (ADA2) and SARS-CoV-2 induced ARDS. We note an interesting link between ADA2 and the chemokine CXCL10 and its receptor CXCR3. By using published datasets of spatial transcriptomics and single-cell RNAseq, we show that ADA2 is highly expressed by inflammatory CD14+CD16+ monocytes, along with profibrotic genes, in lungs affected by COVID-19. This study reveals important associations between key pathophysiological features of ARDS, linking hypoxia, infiltrative CXCR3 monocytes, and a monocyte-derived exoenzyme ADA2.

Clinical spectrum of and outcomes for Indian children with deficiency of adenosine deaminase 2 (DADA2): a multicentric study

OBJECTIVES

Deficiency of adenosine deaminase-2 (DADA2) is a monogenic disorder closely resembling PAN and can present to physicians across various specialties. Through this case series, we aimed to study and describe the clinical spectrum of and outcomes for Indian children with DADA2.

METHODS

The de-identified data from all participating centres were entered in an Excel spreadsheet, and the coordinating centre (All India Institute of Medical Sciences, New Delhi) screened the data for accuracy and completeness.

RESULTS

We enrolled 16 children (11 females) in the study; the mean (s.d.) age at the time of onset of symptoms for males and females was 46.2 (47) and 73.6 (50.4) months, respectively. The most common clinical features in this cohort were fever and rash in 80% of patients. More than half of the children, n (%) [8, (53%)] had a CNS stroke. The other clinical features were hypertension [5(33%)], anaemia [3 (20%)] and arthralgia/arthritis in 4 (26%). These children were managed with various immunomodulators: steroids [13, (86%)], anti-TNF agents [12, (80%)], CYC [2 (13%)] and MMF [3 (20%)]. The median [interquartile range (IQR)] duration of follow-up for this cohort was 17 (10, 29) months. Fourteen children achieved remission, and none had recurrent strokes after the initiation of anti-TNF drugs.

CONCLUSION

DADA-2 closely resembles PAN; early age of onset and CNS stroke are striking differentiating features from classic PAN. Most children respond well to anti-TNF agents without serious adverse events being observed during short-term follow-up.

Intracellular concentration of ADA2 is a marker for monocyte differentiation and activation

Adenosine, a critical molecule regulating cellular function both inside and outside cells, is controlled by two human adenosine deaminases: ADA1 and ADA2. While ADA1 primarily resides in the cytoplasm, ADA2 can be transported to lysosomes within cells or secreted outside the cell. Patients with ADA2 deficiency (DADA2) often suffer from systemic vasculitis due to elevated levels of TNF-α in their blood. Monocytes from DADA2 patients exhibit excessive TNF-α secretion and differentiate into pro-inflammatory M1-type macrophages. Our findings demonstrate that ADA2 localizes to endolysosomes within macrophages, and its intracellular concentration decreases in cells secreting TNF-α. This suggests that ADA2 may function as a lysosomal adenosine deaminase, regulating TNF-α expression by the cells. Interestingly, pneumonia patients exhibit higher ADA2 concentrations in their bronchoalveolar lavage (BAL), correlating with elevated pro-inflammatory cytokine levels. Conversely, cord blood has low ADA2 levels, creating a more immunosuppressive environment. Additionally, secreted ADA2 can bind to apoptotic cells, activating immune cells by reducing extracellular adenosine levels. These findings imply that ADA2 release from monocytes during inflammation, triggered by growth factors, may be crucial for cell activation. Targeting intracellular and extracellular ADA2 activities could pave the way for novel therapies in inflammatory and autoimmune disorders.

Inflammatory disorders that affect the cerebral small vessels

ABSTRACT

This comprehensive review synthesizes the latest advancements in understanding inflammatory disorders affecting cerebral small vessels, a distinct yet understudied category within cerebral small vessel diseases (SVD). Unlike classical SVD, these inflammatory conditions exhibit unique clinical presentations, imaging patterns, and pathophysiological mechanisms, posing significant diagnostic and therapeutic challenges. Highlighting their heterogeneity, this review spans primary angiitis of the central nervous system, cerebral amyloid angiopathy-related inflammation, systemic vasculitis, secondary vasculitis, and vasculitis in autoinflammatory diseases. Key discussions focus on emerging insights into immune-mediated processes, neuroimaging characteristics, and histopathological distinctions. Furthermore, this review underscores the importance of standardized diagnostic frameworks, individualized immunomodulation approaches, and novel targeted therapies to address unmet clinical demands.

Highlights from the breakout session: vasculitis in paediatric rheumatology

The 21st International Vasculitis Workshop, held in Barcelona, Spain, from April 7 to 10, 2024, highlighted advances in pediatric vasculitis, focusing on a holistic, multidisciplinary approach. Common childhood vasculitides, including IgA Vasculitis (IgAV) and Kawasaki Disease (KD), were discussed. The Ankara 2008 criteria for IgAV, endorsed by EULAR and PReS, were evaluated for their performance in adults, showing high sensitivity but necessitating further refinement for improved specificity. Studies on genetic associations, such as Human Leukocyte Antigen (HLA) polymorphisms in IgAV, and biomarkers like S100A8/A9, HMGB1, and RAGE, were presented. Kawasaki disease research included novel anti-apolipoprotein A-2 antibodies, showing promise in reducing coronary arteritis. Monogenic vasculitides, such as deficiency of ADA2, were addressed with new consensus-driven recommendations. The workshop underscored the importance of continued research and tailored therapeutic strategies to improve outcomes in pediatric vasculitis, paving the way for advancements in diagnosis, management, and understanding of these complex diseases.

Early bone marrow alterations in patients with adenosine deaminase 2 deficiency across disease phenotypes and severities

BACKGROUND

Deficiency of adenosine deaminase 2 (DADA2) is a complex monogenic disease caused by recessive mutations in the ADA2 gene. DADA2 exhibits a broad clinical spectrum encompassing vasculitis, immunodeficiency, and hematologic abnormalities. Yet, the impact of DADA2 on the bone marrow (BM) microenvironment is largely unexplored.

OBJECTIVE

This study comprehensively examined the BM and peripheral blood of pediatric and adult patients with DADA2 presenting with rheumatologic/immunologic symptoms or severe hematologic manifestations.

METHODS

Immunophenotyping of hematopoietic stem cells (HSCs), progenitor cells, and mature cell populations was performed for 18 patients with DADA2. We also conducted a characterization of mesenchymal stromal cells.

RESULTS

Our study revealed a significant decrease in primitive HSCs and progenitor cells, alongside their reduced clonogenic capacity and multilineage differentiation potential. These BM defects were evident in patients with both severe and nonsevere hematologic manifestations, including pediatric patients, demonstrating that BM disruption can emerge silently and early on, even in patients who do not show obvious hematologic symptoms. Beyond stem cells, there was a reduction in mature cell populations in the BM and peripheral blood, affecting myeloid, erythroid, and lymphoid populations. Furthermore, BM mesenchymal stromal cells in patients with DADA2 exhibited reduced clonogenic and proliferation capabilities and were more prone to undergo cellular senescence marked by elevated DNA damage.

CONCLUSIONS

Our exploration into the BM landscape of patients with DADA2 sheds light on the critical hematologic dimension of the disease and emphasizes the importance of vigilant monitoring, even in the case of subclinical presentation.

Artificial Nanovesicles Derived from Cells: A Promising Alternative to Extracellular Vesicles

As naturally secreted vesicles by cells, extracellular vesicles (EVs) play essential roles in modulating cell-cell communication and have significant potential in tissue regeneration, immune regulation, and drug delivery. However, the low yield and uncontrollable heterogeneity of EVs have been obstacles to their widespread translation into clinical practice. Recently, it has been discovered that artificial nanovesicles (NVs) produced by cell processing can inherit the components and functions of the parent cells and possess similar structures and functions to EVs, with significantly higher yields and more flexible functionalization, making them a powerful complement to natural EVs. This review focuses on recent advances in the research of artificial NVs as replacements for natural EVs. We provide an overview comparing natural EVs and artificial NVs and summarize the top-down preparation strategies of NVs. The applications of NVs prepared from stem cells, differentiated cells, and engineered cells are presented, as well as the latest advances in NV engineering. Finally, the main challenges of artificial NVs are discussed.

Long-term follow-up of anti-TNF treatment in adult and pediatric DADA2 patients: Insights from real-world data

BACKGROUND/PURPOSE

Our objective was to investigate real-world outcomes and treatment strategies in individuals affected by DADA2 using over 10-year period real-life experience.

METHODS

This descriptive analysis encompassed all adult/pediatric patients with DADA2 from our Vasculitis Research Center prospective database. Patients on anti-TNF therapy have been specifically examined, analyzing the treatment's duration, indications, and outcomes. Treatment responses were based on physicians' assessments and categorized as full response (symptom-free with normal acute phase reactants) or partial/no response.

RESULTS

Totally 32 patients (Adult/Childhood age: 19/13) were analyzed. Anti-TNF agents were prescribed to 27 of the 32 patients. Over a median follow-up of 58 months on anti-TNF therapy, 10 patients (35.7%) exhibited a complete response, predominantly in cases with nervous system or skin involvement. Partial responses were observed in the other 10 patients (35.7%). Currently, 20/ 27 patients remain on anti-TNF treatment. Among the seven who are not on anti-TNF now: five died (four of them with a late diagnosis, one could not continue due to cardiomyopathy), one refused treatment and one had a cure after bone marrow transplantation. We have become aware that four patients increased their dose interval and one returned to the normal interval after an increase in CRP. The first patient was diagnosed in 2013 and over the last 10 years, 6/32 (18.8%) of the patients died.

CONCLUSION

Anti-TNF treatment is beneficial for vasculitic and inflammatory lesions. The clinical course of patients is diverse, especially if the diagnosis is delayed, with a mortality rate of up to 20% over a 10-year period.

Rare primary vasculitis: update on multiple complex diseases and the new kids on the block

Systemic vasculitis is a group of rare diseases that share an essential characteristic: inflammation of blood vessel walls. This injury occurs during the disease course, but specific features vary for each entity. In this paper, we will address relevant aspects of the newest monogenic mutation vasculitis, such as deficiency of adenosine deaminase 2 (ADA2) and VEXAS syndrome (UBA1), and other relevant vasculitis, such as Cogan syndrome and Susac syndrome that may share some similarities with them.

Adenosine deaminase 2 regulates the activation of the toll-like receptor 9 in response to nucleic acids

Human cells contain two types of adenosine deaminases (ADA) each with unique properties: ADA1, which is present in all cells where it modulates intracellular functions and extracellular signaling, and ADA2, which is secreted by immune cells. The exact intracellular functions of ADA2 remain undetermined and less defined than those of ADA1. ADA2 has distinct characteristics, such as low adenosine affinity, heparin-binding ability, and putative lysosomal entry. Here, we confirm that ADA2 is a lysosomal protein that binds toll-like receptor 9 (TLR9) agonists, specifically CpG oligodeoxynucleotides (CpG ODNs). We show that interferon-alpha (IFN-α) is secreted in response to TLR9 activation by CpG ODNs and natural DNA and markedly increases when ADA2 expression is downregulated in plasmacytoid dendritic cells (pDCs). Additionally, the pretreatment of pDCs with RNA further stimulates IFN-α secretion by pDCs after activation with CpG ODNs. Our findings indicate that ADA2 regulates TLR9 responses to DNA in activated pDCs. In conclusion, decreasing ADA2 expression or blocking it with specific oligonucleotides can enhance IFN-α secretion from pDCs, improving immune responses against intracellular infections and cancer.

Human ADA2 Deficiency: Ten Years Later

PURPOSE OF REVIEW

In this review, an update is provided on the current knowledge and pending questions about human adenosine deaminase type 2 deficiency. Patients have vasculitis, immunodeficiency and some have bone marrow failure. Although the condition was described ten years ago, the pathophysiology is incompletely understood RECENT FINDINGS: Endothelial instability due to increased proinflammatory macrophage development is key to the pathophysiology. However, the physiological role of ADA2 is a topic of debate as it is hypothesized that ADA2 fulfils an intracellular role. Increasing our knowledge is urgently needed to design better treatments for the bone marrow failure. Indeed, TNFi treatment has been successful in treating DADA2, except for the bone marrow failure. Major advances have been made in our understanding of DADA2. More research is needed into the physiological role of ADA2.

[Advances in gene therapy for inborn errors of immunity]

Inborn errors of immunity (IEI) are a diverse group of disorders caused by defects in immune system structure or function, involving both innate and adaptive immunity. The 2022 update of the IEI classification includes 485 distinct disorders, categorized into ten major disease groups. With the rapid development of molecular biology, the specific pathogenesis of many IEI has been revealed, making gene therapy possible in preclinical and clinical research of this type of disease. This article reviews the advancements in gene therapy for IEI, aiming to increase awareness and understanding of these disorders.

ADA2 regulates inflammation and hematopoietic stem cell emergence via the A2bR pathway in zebrafish

Deficiency of adenosine deaminase 2 (DADA2) is an inborn error of immunity caused by loss-of-function mutations in the adenosine deaminase 2 (ADA2) gene. Clinical manifestations of DADA2 include vasculopathy and immuno-hematological abnormalities, culminating in bone marrow failure. A major gap exists in our knowledge of the regulatory functions of ADA2 during inflammation and hematopoiesis, mainly due to the absence of an ADA2 orthologue in rodents. Exploring these mechanisms is essential for understanding disease pathology and developing new treatments. Zebrafish possess two ADA2 orthologues, cecr1a and cecr1b, with the latter showing functional conservation with human ADA2. We establish a cecr1b-loss-of-function zebrafish model that recapitulates the immuno-hematological and vascular manifestations observed in humans. Loss of Cecr1b disrupts hematopoietic stem cell specification, resulting in defective hematopoiesis. This defect is caused by induced inflammation in the vascular endothelium. Blocking inflammation, pharmacological modulation of the A2r pathway, or the administration of the recombinant human ADA2 corrects these defects, providing insights into the mechanistic link between ADA2 deficiency, inflammation and immuno-hematological abnormalities. Our findings open up potential therapeutic avenues for DADA2 patients.

Adenosine deaminase 2 deficiency in a Chinese patient: Report of one novel mutation and literature review

OBJECTIVE

Through a case of deficiency of adenosine deaminase 2 (DADA2) to improve domestic clinicians' understanding of the disease, and to review the literature, promote dermatologists for clinical secondary primary lesion diagnosis.

METHOD

Analysis of a case diagnosed with DADA2 deficiency of clinical manifestations, laboratory, imaging examination and treatment methods, and discussion through literature analysis.

RESULTS

The child with recurrent fever, limbs nodular erythema, gradually in the limbs. CT of lower limb skin showed mild edema of the spinous layer, intact basal layer, dilated vascular congestion in the superficial dermis, visible RBC extravasation, and changes of telangiectasia ring purpura were considered. Cranial magnetic resonance imaging (MRI) showed a left choroidal cleft cyst. Genetic test was the CECR1 mutation. The treatment with adalimumab was effective.

CONCLUSION

In this case, DADA2 is the seventh case in China, and the CECR1 mutation site (c.254A> T p.N85I,c.851G>T p. G284V) was a compound heterozygous mutation. Mastering the clinical characteristics is helpful for clinicians to diagnose this disease.

Neurological phenotype of adenosine deaminase 2 deficient patients: a cohort study

BACKGROUND AND PURPOSE

Patients with adenosine deaminase 2 (ADA2) deficiency can present with various neurological manifestations due to vasculopathies and autoinflammation. These include ischaemic and hemorrhagic stroke, but less clearly defined neurological symptoms have also been reported.

METHODS

In this cohort study, patients with confirmed ADA2 deficiency from seven university hospitals in the Netherlands were included. The frequency and recurrence rates of neurological manifestations before and after initiation of tumor necrosis factor α (TNF-α) inhibiting therapy were analyzed.

RESULTS

Twenty-nine patients were included with a median age at presentation of 5 years (interquartile range 1-17). Neurological manifestations occurred in 19/29 (66%) patients and were the presenting symptom in 9/29 (31%) patients. Transient ischaemic attack (TIA)/ischaemic stroke occurred in 12/29 (41%) patients and was the presenting symptom in 8/29 (28%) patients. In total, 25 TIAs/ischaemic strokes occurred in 12 patients, one after initiation of TNF-α inhibiting therapy and one whilst switching between TNF-α inhibitors. None was large-vessel occlusion stroke. Two hemorrhagic strokes occurred: one aneurysmatic subarachnoid hemorrhage and one spontaneous intracerebral hemorrhage. Most neurological symptoms, including cranial nerve deficits, vertigo, ataxia and seizures, were caused by TIAs/ischaemic strokes and seldom recurred after initiation of TNF-α inhibiting therapy.

CONCLUSIONS

Neurological manifestations, especially TIA/ischaemic stroke, are common in patients with ADA2 deficiency and frequently are the presenting symptom. Because it is a treatable cause of young stroke, for which antiplatelet and anticoagulant therapy are considered contraindicated, awareness amongst neurologists and pediatricians is important. Screening for ADA2 deficiency in young patients with small-vessel ischaemic stroke without an identified cause should be considered.

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 Narrative Review of the Neurological Manifestations of Human Adenosine Deaminase 2 Deficiency

Deficiency of human adenosine deaminase type 2 (DADA2) is a complex systemic autoinflammatory disorder characterized by vasculopathy, immune dysregulation, and hematologic abnormalities. The most notable neurological manifestations of DADA2 are strokes that can manifest with various neurological symptoms and are potentially fatal. However, neurological presentations can be diverse. We here present a review of the neurological manifestations of DADA2 to increase clinical awareness of DADA2 as the underlying diagnosis. We reviewed all published cases of DADA2 from 1 January 2014 until 19 July 2022 found via PubMed. A total of 129 articles describing the clinical features of DADA2 were included in the analysis. Six hundred twenty-eight patients diagnosed with DADA2 were included in the review. 50.3% of patients had at least signs of one reported neurological event, which was the initial or sole manifestation in 5.7% and 0.6%, respectively. 77.5% of patients with neurological manifestations had at least signs of one cerebrovascular accident, with lacunar strokes being the most common and 35.9% of them having multiple stroke episodes. There is a remarkable predilection for the brain stem and deep gray matter, with 37.3% and 41.6% of ischemic strokes, respectively. Other neurological involvement included neuropathies, focal neurological deficits, ophthalmological findings, convulsions, and headaches. In summary, neurological manifestations affect a significant proportion of patients with DADA2, and the phenotype is broad. Neurological manifestations can be the first and single manifestation of DADA2. Therefore, stroke, encephalitis, posterior reversible encephalopathy syndrome, mononeuropathy and polyneuropathy, and Behçet's disease-like presentations should prompt the neurologist to exclude DADA2, especially but not only in childhood.

Cerebral Aneurysms and Recurrent TIAs in a 42-Year-Old Patient With DADA2 Mutation: A Case Report

Objectives

Deficiency of adenosine deaminase 2 (DADA2) is a rare, recessively inherited autoinflammatory disease with a wide clinical spectrum of manifestations, including strokes and vasculitis.

Methods

We report a case of a patient with DADA2 who presented with neurologic manifestations.

Results

A 42-year-old woman with a known diagnosis of polyarteritis nodosa experienced several episodes of TIAs. Neuroimaging revealed 2 aneurysms in unusual locations. Her young age, ethnic origin, absent of cardiovascular risk factors, and skin involvement raised the suspicion of DADA2. Genetic testing confirmed the diagnosis, and a directed treatment with anti-TNF was initiated.

Discussion

DADA2, although thought to be rare, needs to be borne in mind when evaluating patients with a combination of neurologic and systemic symptoms, as early diagnosis and treatment are imperative in preventing permanent disability.

Comparison of disease phenotypes and mechanistic insight on causal variants in patients with DADA2

BACKGROUND

Deficiency of adenosine deaminase 2 (DADA2) results in heterogeneous manifestations including systemic vasculitis and red cell aplasia. The basis of different disease phenotypes remains incompletely defined.

OBJECTIVE

We sought to further delineate disease phenotypes in DADA2 and define the mechanistic basis of ADA2 variants.

METHODS

We analyzed the clinical features and ADA2 variants in 33 patients with DADA2. We compared the transcriptomic profile of 14 patients by bulk RNA sequencing. ADA2 variants were expressed experimentally to determine impact on protein production, trafficking, release, and enzymatic function.

RESULTS

Transcriptomic analysis of PBMCs from DADA2 patients with the vasculitis phenotype or pure red cell aplasia phenotype exhibited similar upregulation of TNF, type I interferon, and type II interferon signaling pathways compared with healthy controls. These pathways were also activated in 3 asymptomatic individuals with DADA2. Analysis of ADA2 variants, including 7 novel variants, showed different mechanisms of functional disruption including (1) unstable transcript leading to RNA degradation; (2) impairment of ADA2 secretion because of retention in the endoplasmic reticulum; (3) normal expression and secretion of ADA2 that lacks enzymatic function; and (4) disruption of the N-terminal signal peptide leading to cytoplasmic localization of unglycosylated protein.

CONCLUSIONS

Transcriptomic signatures of inflammation are observed in patients with different disease phenotypes, including some asymptomatic individuals. Disease-associated ADA2 variants affect protein function by multiple mechanisms, which may contribute to the clinical heterogeneity of DADA2.

Interferonopathies masquerading as non-Mendelian autoimmune diseases: pattern recognition for early diagnosis

Type I interferonopathies are a broad category of conditions associated with increased type I interferon gene expression and include monogenic autoinflammatory diseases and non-Mendelian autoimmune diseases such as dermatomyositis and systemic lupus erythematosus. While a wide range of clinical presentations among type I interferonopathies exists, these conditions often share several clinical manifestations and implications for treatment. Presenting symptoms may mimic non-Mendelian autoimmune diseases, including vasculitis and systemic lupus erythematosus, leading to delayed or missed diagnosis. This review aims to raise awareness about the varied presentations of monogenic interferonopathies to provide early recognition and appropriate treatment to prevent irreversible damage and improve quality of life and outcomes in this unique patient population.

Delayed-onset adenosine deaminase deficiency with a novel synonymous mutation and a case series from China

BACKGROUND

Adenosine deaminase (ADA) is a key enzyme in the purine salvage pathway. Genetic defects of the ADA gene can cause a subtype of severe combined immunodeficiency. To date, few Chinese cases have been reported.

METHODS

We retrospectively reviewed the medical records of patients diagnosed with ADA deficiency in Beijing Children's Hospital and summarized the previously published ADA deficiency cases from China in the literature.

RESULTS

Nine patients were identified with two novel mutations (W272X and Q202 =). Early-onset infection, thymic abnormalities and failure to thrive were the most common manifestations of Chinese ADA-deficient patients. The ADA genotype has a major effect on the clinical phenotype. Notably, a novel synonymous mutation (c.606G>A, p.Q202=) was identified in a delayed-onset patient, which affected pre-mRNA splicing leading to a frameshift and premature truncation of the protein. Furthermore, the patient showed γδT cells expansion with an increased effect or phenotype, which may be associated with the delayed onset of disease. In addition, we reported cerebral aneurysm and intracranial artery stenosis for the first time in ADA deficiency. Five patients died with a median age of four months, while two patients received stem cell transplantation and are alive.

CONCLUSIONS

This study described the first case series of Chinese ADA-deficient patients. Early-onset infection, thymic abnormalities and failure to thrive were the most common manifestations in our patients. We identified a synonymous mutation that affected pre-mRNA splicing in the ADA gene, which had never been reported in ADA deficiency. Furthermore, we reported cerebral aneurysm in a delayed-onset patient for the first time. Further study is warranted to investigate the underlying mechanisms.

Case Report: Patient with deficiency of ADA2 presenting leukocytoclastic vasculitis and pericarditis during infliximab treatment

Deficiency of adenosine deaminase 2 (DADA2), first reported in 2014, is a disease with great phenotypic variability, which has been increasingly reported. Therapeutic response depends on the phenotype. We present a case of an adolescent with recurrent fever, oral aphthous ulcers, and lymphadenopathy from 8 to 12 years of age and subsequently presented with symptomatic neutropenia. After the diagnosis of DADA2, therapy with infliximab was started, but after the second dose, she developed leukocytoclastic vasculitis and showed symptoms of myopericarditis. Infliximab was switched to etanercept, with no relapses. Despite the safety of tumor necrosis factor alpha inhibitors (TNFi), paradoxical adverse effects have been increasingly reported. The differential diagnosis between disease new-onset manifestations of DADA2 and side effects of TNFi can be challenging and warrants further clarification.

A Cohort Study on Deficiency of ADA2 from China

PURPOSE

Deficiency of adenosine deaminase 2 (DADA2), an autosomal recessive autoinflammatory disorder caused by biallelic loss-of-function variants in adenosine deaminase 2 (ADA2), has not been systemically investigated in Chinese population yet. We aim to further characterize DADA2 cases in China.

METHODS

A retrospective analysis of patients with DADA2 identified through whole exome sequencing (WES) at seventeen rheumatology centers across China was conducted. Clinical characteristics, laboratory findings, genotype, and treatment response were analyzed.

RESULTS

Thirty patients with DADA2 were enrolled between January 2015 and December 2021. Adenosine deaminase 2 enzymatic activity was low in all tested cases to confirm pathogenicity. Median age of disease presentation was 4.3 years and the median age at diagnosis was 7.8 years. All but one patient presented during childhood and two subjects died from complications of their disease. The patients most commonly presented with systemic inflammation (92.9%), vasculitis (86.7%), and hypogammaglobinemia (73.3%) while one patient presented with bone marrow failure (BMF) with variable cytopenia. Twenty-three (76.7%) patients were treated with TNF inhibitors (TNFi), while two (6.7%) underwent hematopoietic stem cell transplantation (HSCT). They all achieved clinical remission. A total of thirty-nine ADA2 causative variants were identified, six of which were novel.

CONCLUSION

To establish early diagnosis and improve clinical outcomes, genetic screening and/or testing of ADA2 enzymatic activity should be performed in patients with suspected clinical features. TNFi is considered as first line treatment for those with vascular phenotypes. HSCT may be beneficial for those with hematological disease or in those who are refractory to TNFi.

Positron Emission Tomography Imaging in Vasculitis

Systemic vasculitides comprise a group of autoimmune diseases affecting blood vessels. [18F]-fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (FDG-PET/CT) plays an important role in the diagnosis and therapeutic monitoring of vasculitides affecting large-sized and medium-sized vessels. FDG-PET/CT also provides complementary information to other vascular imaging tools. The resolution and sensitivity of newer generation scanners continues to increase, hereby improving the ability of FDG-PET/CT to accurately assess the full disease extent in patients with vasculitis. Novel tracers targeting specific immune cells will allow for more detailed detection of vascular infiltrates.

The neutrophil: A key resourceful agent in immune‐mediated vasculitis

The term "vasculitis" refers to a group of rare immune-mediated diseases characterized by the dysregulated immune system attacking blood vessels located in any organ of the body, including the skin, lungs, and kidneys. Vasculitides are classified according to the size of the vessel that is affected. Although this observation is not specific to small-, medium-, or large-vessel vasculitides, patients show a high circulating neutrophil-to-lymphocyte ratio, suggesting the direct or indirect involvement of neutrophils in these diseases. As first responders to infection or inflammation, neutrophils release cytotoxic mediators, including reactive oxygen species, proteases, and neutrophil extracellular traps. If not controlled, this dangerous arsenal can injure the vascular system, which acts as the main transport route for neutrophils, thereby amplifying the initial inflammatory stimulus and the recruitment of immune cells. This review highlights the ability of neutrophils to "set the tone" for immune cells and other cells in the vessel wall. Considering both their long-established and newly described roles, we extend their functions far beyond their direct host-damaging potential. We also review the roles of neutrophils in various types of primary vasculitis, including immune complex vasculitis, anti-neutrophil cytoplasmic antibody-associated vasculitis, polyarteritis nodosa, Kawasaki disease, giant cell arteritis, Takayasu arteritis, and Behçet's disease.

ELISA based assays to measure adenosine deaminases concentration in serum and saliva for the diagnosis of ADA2 deficiency and cancer

Adenosine deaminases (ADAs) are enzymes of purine metabolism converting adenosine to inosine. There are two types of ADAs in humans ADA1 and ADA2. While both ADA1 and ADA2 share the same substrate, they differ in expression, cellular localization, and catalytic properties. The genetic deficiency of ADA1 results in severe combined immunodeficiency (SCID), while lack in ADA2 (DADA2) results in multiple phenotypes ranging from systemic inflammation to vascular pathology. Clinical studies have shown that the levels of ADAs in biological fluids are altered in pathophysiological conditions, suggesting that ADA activity could be a convenient marker for the diagnosis of immune diseases and cancer. Here, we describe sensitive and straightforward ELISA assays to measure ADA1 and ADA2 concentrations in biological fluids. Analysis of the serum and saliva samples from the healthy controls and DADA2 patients revealed that ADA2 enzyme concentration is significantly lower in patients than in healthy controls. In contrast, the concentration of ADA2 increases in the serum of patients with large granular leukocyte leukemia (LGLL) and patients’ saliva with head and neck cancer. Thus, this simple, non-invasive method allows for distinguishing healthy controls from the affected patient. It can be implemented in screening and diagnosis of DADA2 and follow up the treatment of LGLL and several types of head and neck cancer.

Adenosine Deaminase 2 Deficiency (DADA2): A Crosstalk Between Innate and Adaptive Immunity

Deficiency of Adenosine deaminase 2 (DADA2) is a monogenic autoinflammatory disorder presenting with a broad spectrum of clinical manifestations, including immunodeficiency, vasculopathy and hematologic disease. Biallelic mutations in ADA2 gene have been associated with a decreased ADA2 activity, leading to reduction in deamination of adenosine and deoxyadenosine into inosine and deoxyinosine and subsequent accumulation of extracellular adenosine. In the early reports, the pivotal role of innate immunity in DADA2 pathogenic mechanism has been underlined, showing a skewed polarization from the M2 macrophage subtype to the proinflammatory M1 subtype, with an increased production of inflammatory cytokines such as TNF-α. Subsequently, a dysregulation of NETosis, triggered by the excess of extracellular Adenosine, has been implicated in the pathogenesis of DADA2. In the last few years, evidence is piling up that adaptive immunity is profoundly altered in DADA2 patients, encompassing both T and B branches, with a disrupted homeostasis in T-cell subsets and a B-cell skewing defect. Type I/type II IFN pathway upregulation has been proposed as a possible core signature in DADA2 T cells and monocytes but also an increased IFN-β secretion directly from endothelial cells has been described. So far, a unifying clear pathophysiological explanation for the coexistence of systemic inflammation, immunedysregulation and hematological defects is lacking. In this review, we will explore thoroughly the latest understanding regarding DADA2 pathophysiological process, with a particular focus on dysregulation of both innate and adaptive immunity and their interacting role in the development of the disease.

Allogeneic Hematopoietic Cell Transplantation for Patients With Deficiency of Adenosine Deaminase 2 (DADA2): Approaches, Obstacles and Special Considerations

Deficiency of adenosine deaminase 2 (DADA2) is an inherited autosomal recessive disease characterized by autoinflammation (recurrent fever), vasculopathy (livedo racemosa, polyarteritis nodosa, lacunar ischemic strokes, and intracranial hemorrhages, end organ vasculitis), immunodeficiency, lymphoproliferation, immune cytopenias, and bone marrow failure. Allogeneic hematopoietic cell transplantation (HCT) is curative for DADA2 as it reverses the hematological, immune and vascular phenotype of DADA2. The primary goal of HCT in DADA2, like in other non-malignant diseases, is engraftment with the establishment of normal hematopoiesis and normal immune function. Strategies in selecting a preparative regimen should take into consideration the specific vulnerabilities to endothelial dysfunction and liver toxicity in DADA2 patients. Overcoming an increased risk of graft rejection while minimizing organ toxicity, graft-versus-host disease, and infections can be particularly challenging in DADA2 patients. This review will discuss approaches to HCT in DADA2 patients including disease-specific considerations, barriers to successful engraftment, post-HCT complications, and clinical outcomes of published patients with DADA2 who have undergone HCT to date.

Clinical presentation of children with Deficiency of Adenosine deaminase 2: A case series

Deficiency of Adenosine deaminase 2 (DADA2) is a monogenic inflammatory disease, caused by mutations in ADA2 gene, which encodes an extracellular enzyme acting as a monocyte differentiation factor. DADA2 is first described with the clinical picture resembling polyarteritis nodosa, including livedo racemose, recurrent fever, musculoskeletal complaints. Besides, some patients have cytopenia, lymphoproliferation and mild to moderate immunodeficiency. The most crucial complication of DADA2 is neurological involvement, especially arterial stroke, which necessitates continuous treatment with anti-tumor necrosis factor α (anti-TNFα) treatment for preventing further stroke attacks. Herein, we report 5 DADA2 patients from 5 unrelated families, all had G47R mutation in at least one allele. All patients had livedo racemose, and 4 patients suffered from recurrent fever. Besides, musculoskeletal complaints and gastrointestinal symptoms were present in 4 and 3 patients, respectively. One patient had chronic arthritis and only one patient had a history of recurrent stroke without any sequela. Hematological and immunological involvement occurred in 3 and 4 patients, respectively, whereas only one had significant panhypogammaglobulinemia, requiring replacement therapy. We started etanercept treatment to all patients, which resulted the complete resolution of systemic inflammatory attacks and skin lesions and provided neurologically symptom free during their follow-up. With this report, we emphasize the importance of early referral of the patients with suspected livedo racemose to avoid the delay of DADA2 diagnosis for favorable outcome.