Deficiency of Adenosine Deaminase 2

Adenosine deaminase 2 (ADA2) deficiency is an autosomal recessively inherited autoinflammatory disorder caused by loss-of-function mutations in the ADA2 gene. Although the pathogenesis involves the triggering of a proinflammatory cascade due to increased production of inflammatory cytokines such as tumor necrosis factor (TNF)-α and dysregulation of neutrophil extracellular trap formation resulting from an excess accumulation of extracellular adenosine, the pathogenetic mechanism still needs further clarification due to the broad clinical spectrum. In addition to the initially described vasculitis-related symptoms, hematological, immunological, and autoinflammatory symptoms are now well recognized. The diagnosis is made by demonstration of pathogenic variants of ADA2 with biallelic loss of function and identification of low plasma ADA2 catalytic activity. Currently, TNF-α inhibitors are the treatment of choice for controlling vasculitis manifestations and preventing strokes. However, in patients presenting with severe hematologic findings, TNF-α inhibitors are not the treatment of choice and hematopoietic stem cell transplantation has been shown to be successful in selected cases. Recombinant ADA2 protein and gene therapy are promising treatment modalities for the future. In conclusion, ADA2 deficiency has a broad phenotype and should be considered in the differential diagnosis of different clinical situations. In this review, we summarize the disease manifestations of ADA2 deficiency and available treatment options.

A Clinical Neurological Approach to the Child With Adenosine Deaminase Deficiency.

BACKGROUND: Severe combined immunodeficiency secondary to adenosine deaminase deficiency is rare. The deficiency of this enzyme results in the accumulation of substrates in the tissues, including the brain. Clinical signs of neurological involvement may include seizures, neurodevelopmental disorders, hypotonia, and sensorineural hearing loss. Hematopoietic stem cell transplantation corrects the failure of the immune system but not the neurological involvement. OBJECTIVES: To describe the spectrum of neurological complications identified in a series of children with severe combined immunodeficiency due to adenosine deaminase deficiency. Additionally, we propose a neurological approach including electrophysiological, radiological, and neurocognitive studies to address this group of children in an efficient and timely manner. METHODS: A descriptive, observational, retro-, and prospective analysis of patients with a confirmed immunological diagnosis seen between 1996 and 2021 and referred to the Department of Neurology for neurological evaluation was conducted. RESULTS: Ten patients met the inclusion criteria. The median age at diagnosis was 4 months (range, 1-36 months). All patients had neurodevelopmental delay with hypotonia in six, language delay in three, sensorineural hearing loss in four, and spastic paraparesis in one patient. Two children developed an epileptic syndrome, consisting of generalized epilepsy in one and focal epilepsy in the other. Neuroimaging showed brain calcifications in the basal ganglia and/or centrum semiovale in four patients and enlarged subarachnoid spaces in two other patients. CONCLUSION: In this pediatric series, the rate of neurological involvement associated with abnormalities on neuroimaging was high. Although this involvement could be related to accumulation of adenosine metabolites in the central nervous system, the possibility of associated chronic infections should be ruled out. Given the neurological manifestations, it is important to involve the pediatric neurologist in the multidisciplinary follow-up team.

Negative features of sporadic amyotrophic lateral sclerosis: Motor neurons of Onuf's nucleus survive in ADAR2-conditional knockout mice.

Patients with amyotrophic lateral sclerosis (ALS) do not develop oculomotor disturbances and vesicorectal dysfunction until end-stage disease owing to the survival of certain motor neurons (MNs), including oculomotor neurons and MNs within Onuf's nucleus. In sporadic ALS, adenosine deaminase acting on RNA 2 (ADAR2)-mediated editing of GluA2 mRNA at the Q/R site is compromised in lower MNs. We previously developed genetically modified mice with a conditional knockout of ADAR2 in cholinergic neurons (ADAR2flox/flox/VAChT-Cre, Fast; AR2). These mice displayed slow and progressive lower motor neuron death with TAR DNA-binding protein 43 (TDP-43) pathology, attributable to insufficient editing at the GluA2 Q/R site due to ADAR2 deficiency. MN death was more common in fast-fatigable MNs owing to differential vulnerability under conditions of ADAR2 deficiency. Although facial and hypoglossal nerves were impaired in AR2 mice, cell death did not occur within the oculomotor nerve nucleus, as observed in patients with sporadic ALS. Since the basis for avoiding cystorectal damage in ALS is unknown, we compared the features of Onuf's nucleus MNs in 12-month-old AR2 mice with those in age-matched wild-type mice. Although the number of MNs was not significantly lower in AR2 mice, the neurons exhibited a shrunken morphology and TDP-43 pathology. Onuf's nucleus MNs could survive in an ADAR2-deficient state and mainly included fast fatigue-resistant (FR) and slow (S) MNs. In summary, FR and S MNs show increased resilience to ADAR2 deficiency, potentially participating in an important neuronal death avoidance mechanism in ALS.

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.

Development of EBV Related Diffuse Large B-cell Lymphoma in Deficiency of Adenosine Deaminase 2 with Uncontrolled EBV Infection.

Deficiency of Adenosine Deaminase 2 (DADA2) patients presenting with primary immunodeficiency are at risk of uncontrolled EBV infection and secondary malignancies including EBV-related lymphoproliferative disorders (LPD). This paper describes the first case of EBV related diffuse large B-cell lymphoma in a patient with DADA2 and uncontrolled EBV infection. Consideration should be given to monitoring for EBV viraemia and to preventative EBV specific therapy in DADA2 and patients with at risk primary immunodeficiencies. A type I interferon (IFN) gene signature is associated with DADA2 though its association with immune dysregulation is unclear.

Deficiency of adenosine deaminase 2: a genetic autoinflammatory disorder mimicking childhood polyarteritis nodosa.

A girl in the early adolescent age group presented with multisystem manifestations in the form of periodic fever, recurrent abdominal pain, hypertension, seizure, skin lesions over the chest and gangrene over the left ring and middle fingertips. Her condition had remained undiagnosed for 11 years. On evaluation, she had features of polyarteritis nodosa (PAN) (multiple aneurysms, symmetric sensorimotor peripheral neuropathy, superficial ulcers, digital necrosis, myalgia, hypertension and proteinuria). As childhood PAN is a phenocopy of adenosine deaminase 2 with a different management strategy, whole-exome sequencing was performed, which revealed a pathogenic variant in ADA2 gene. The child was treated with TNF alpha inhibitors and showed improvement in the Paediatric Vasculitis Activity Score. The paper highlights the gratifying consequences of correct diagnosis with disease-specific therapy that ended the diagnostic odyssey, providing relief to the patient from debilitating symptoms and to the family from the financial burden of continued out-of-pocket health expenditure.

Deficiency of ADAR2 ameliorates metabolic-associated fatty liver disease via AMPK signaling pathways in obese mice.

Non-alcoholic fatty liver disease (NAFLD) is a chronic disease caused by hepatic steatosis. Adenosine deaminases acting on RNA (ADARs) catalyze adenosine to inosine RNA editing. However, the functional role of ADAR2 in NAFLD is unclear. ADAR2+/+/GluR-BR/R mice (wild type, WT) and ADAR2-/-/GluR-BR/R mice (ADAR2 KO) mice are fed with standard chow or high-fat diet (HFD) for 12 weeks. ADAR2 KO mice exhibit protection against HFD-induced glucose intolerance, insulin resistance, and dyslipidemia. Moreover, ADAR2 KO mice display reduced liver lipid droplets in concert with decreased hepatic TG content, improved hepatic insulin signaling, better pyruvate tolerance, and increased glycogen synthesis. Mechanistically, ADAR2 KO effectively mitigates excessive lipid production via AMPK/Sirt1 pathway. ADAR2 KO inhibits hepatic gluconeogenesis via the AMPK/CREB pathway and promotes glycogen synthesis by activating the AMPK/GSK3ß pathway. These results provide evidence that ADAR2 KO protects against NAFLD progression through the activation of AMPK signaling pathways.

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.

Treatment with Elapegademase Restores Immunity in Infants with Adenosine Deaminase Deficient Severe Combined Immunodeficiency.

PURPOSE: Patients with adenosine deaminase 1 deficient severe combined immunodeficiency (ADA-SCID) are initially treated with enzyme replacement therapy (ERT) with polyethylene glycol-modified (PEGylated) ADA while awaiting definitive treatment with hematopoietic stem cell transplant (HSCT) or gene therapy. Beginning in 1990, ERT was performed with PEGylated bovine intestinal ADA (ADAGEN®). In 2019, a PEGylated recombinant bovine ADA (Revcovi®) replaced ADAGEN following studies in older patients previously treated with ADAGEN for many years. There are limited longitudinal data on ERT-naïve newborns treated with Revcovi. METHODS: We report our clinical experience with Revcovi as initial bridge therapy in three newly diagnosed infants with ADA-SCID, along with comprehensive biochemical and immunologic data. RESULTS: Revcovi was initiated at twice weekly dosing (0.2 mg/kg intramuscularly), and monitored by following plasma ADA activity and the concentration of total deoxyadenosine nucleotides (dAXP) in erythrocytes. All patients rapidly achieved a biochemically effective level of plasma ADA activity, and red cell dAXP were eliminated within 2-3 months. Two patients reconstituted B-cells and NK-cells within the first month of ERT, followed by naive T-cells one month later. The third patient reconstituted all lymphocyte subsets within the first month of ERT. One patient experienced declining lymphocyte counts with improvement following Revcovi dose escalation. Two patients developed early, self-resolving thrombocytosis, but no thromboembolic events occurred. CONCLUSION: Revcovi was safe and effective as initial therapy to restore immune function in these newly diagnosed infants with ADA-SCID, however, time course and degree of reconstitution varied. Revcovi dose may need to be optimized based on immune reconstitution, clinical status, and biochemical data.

A case of T-cell acute lymphoblastic leukemia in retroviral gene therapy for ADA-SCID.

Hematopoietic stem cell gene therapy (GT) using a γ-retroviral vector (γ-RV) is an effective treatment for Severe Combined Immunodeficiency due to Adenosine Deaminase deficiency. Here, we describe a case of GT-related T-cell acute lymphoblastic leukemia (T-ALL) that developed 4.7 years after treatment. The patient underwent chemotherapy and haploidentical transplantation and is currently in remission. Blast cells contain a single vector insertion activating the LIM-only protein 2 (LMO2) proto-oncogene, confirmed by physical interaction, and low Adenosine Deaminase (ADA) activity resulting from methylation of viral promoter. The insertion is detected years before T-ALL in multiple lineages, suggesting that further hits occurred in a thymic progenitor. Blast cells contain known and novel somatic mutations as well as germline mutations which may have contributed to transformation. Before T-ALL onset, the insertion profile is similar to those of other ADA-deficient patients. The limited incidence of vector-related adverse events in ADA-deficiency compared to other γ-RV GT trials could be explained by differences in transgenes, background disease and patient's specific factors.

A case report on deficiency of adenosine deaminase 2 with relapse-remission course and analysis of genotype-phenotype correlation.

Deficiency of adenosine deaminase 2 (DADA2) is a monogenic disease caused by biallelic mutations in adenosine deaminase 2 (ADA2). The varying phenotypes of the disease often lead to delayed diagnosis or misdiagnosis. We report an 11-year-old boy with DADA2 and provide a preliminary analysis of genotype-phenotype correlation. The age of onset of the disease was 8 years old. The disease successively involved the brainstem, muscles, joints, and cerebrum. After three relapse-remission episodes over 3 years, the patient was finally diagnosed with DADA2 by whole-exome sequencing. Compound heterozygous variants in the ADA2 gene (NM_001282225.2: c.1072G>A, p.Gly358Arg; c.419dupC, p.Arg141Lysfs*37) were found in the patient. He did not receive anti-TNF therapy and had no relapse after a 8-month follow-up. We identified a novel variant of the ADA2 gene, and the associated disease course may follow a relapse-remission pattern. Homozygous mutations of p.Gly358Arg can cause pure red cell aplasia, whereas compound heterozygous variations may lead to different phenotypes. Variants in the catalytic domain and frameshift mutations may also cause relatively benign phenotypes besides causing hematological disorders. Further studies are needed to clarify the genotypic-phenotypic relationship of this disease.

Childhood Vasculitis.

Of the primary vasculitis pediatricians are familiar with, Kawasaki disease and IgA vasculitis are the most common. The other large, medium and small vessel vasculitis are seldom seen in practice. Though rare, early diagnosis and appropriate management is critical for the best outcome. Primary vasculitis in the pediatric age group have several differential diagnoses which range from infections to monogenic causes such as deficiency of Adenosine Deaminase -2. Each child, therefore, needs a careful systematic approach.

Histiocytoid Sweet Syndrome Presenting in Two Sisters With Deficiency of Deaminase Type 2.

ABSTRACT: Deficiency of adenosine deaminase type 2 (DADA2) is an autosomal recessive monogenic autoinflammatory syndrome that is classically characterised by polyarteritis nodosa, systemic vasculitis and stroke. The spectrum of disease manifestations has broadened to encompass a range of cutaneous, vascular and haematological manifestations. We report a novel association in two sisters with heterozygous p.R169G/p.M309l mutations in ADA2 with low serum ADA2 activity who both presented similarly with clinical and histological features consistent with histiocytoid Sweet syndrome.

ADAR1 prevents autoinflammation by suppressing spontaneous ZBP1 activation.

The RNA-editing enzyme adenosine deaminase acting on RNA 1 (ADAR1) limits the accumulation of endogenous immunostimulatory double-stranded RNA (dsRNA)1. In humans, reduced ADAR1 activity causes the severe inflammatory disease Aicardi-Goutières syndrome (AGS)2. In mice, complete loss of ADAR1 activity is embryonically lethal3-6, and mutations similar to those found in patients with AGS cause autoinflammation7-12. Mechanistically, adenosine-to-inosine (A-to-I) base modification of endogenous dsRNA by ADAR1 prevents chronic overactivation of the dsRNA sensors MDA5 and PKR3,7-10,13,14. Here we show that ADAR1 also inhibits the spontaneous activation of the left-handed Z-nucleic acid sensor ZBP1. Activation of ZBP1 elicits caspase-8-dependent apoptosis and MLKL-mediated necroptosis of ADAR1-deficient cells. ZBP1 contributes to the embryonic lethality of Adar-knockout mice, and it drives early mortality and intestinal cell death in mice deficient in the expression of both ADAR and MAVS. The Z-nucleic-acid-binding Zα domain of ADAR1 is necessary to prevent ZBP1-mediated intestinal cell death and skin inflammation. The Zα domain of ADAR1 promotes A-to-I editing of endogenous Alu elements to prevent dsRNA formation through the pairing of inverted Alu repeats, which can otherwise induce ZBP1 activation. This shows that recognition of Alu duplex RNA by ZBP1 may contribute to the pathological features of AGS that result from the loss of ADAR1 function.

Catalytically active holo Homo sapiens adenosine deaminase I adopts a closed conformation.

Homo sapiens adenosine deaminase 1 (HsADA1; UniProt P00813) is an immunologically relevant enzyme with roles in T-cell activation and modulation of adenosine metabolism and signaling. Patients with genetic deficiency in HsADA1 suffer from severe combined immunodeficiency, and HsADA1 is a therapeutic target in hairy cell leukemias. Historically, insights into the catalytic mechanism and the structural attributes of HsADA1 have been derived from studies of its homologs from Bos taurus (BtADA) and Mus musculus (MmADA). Here, the structure of holo HsADA1 is presented, as well as biochemical characterization that confirms its high activity and shows that it is active across a broad pH range. Structurally, holo HsADA1 adopts a closed conformation distinct from the open conformation of holo BtADA. Comparison of holo HsADA1 and MmADA reveals that MmADA also adopts a closed conformation. These findings challenge previous assumptions gleaned from BtADA regarding the conformation of HsADA1 that may be relevant to its immunological interactions, particularly its ability to bind adenosine receptors. From a broader perspective, the structural analysis of HsADA1 presents a cautionary tale for reliance on homologs to make structural inferences relevant to applications such as protein engineering or drug development.

Single-cell profiling of T lymphocytes in deficiency of adenosine deaminase 2.

Deficiency of adenosine deaminase 2 (DADA2) is a monogenic vasculitis syndrome caused by autosomal-recessive loss-of-function mutations in the ADA2 gene (previously known as CECR1). Vasculitis, vasculopathy, and inflammation are dominant clinical features of this disease; the spectrum of manifestations includes immunodeficiency and lymphoproliferation as well as hematologic manifestations. ADA2 is primarily secreted by stimulated monocytes and macrophages. Aberrant monocyte differentiation to macrophages and neutrophils are important in the pathogenesis of DADA2, but little is known about T lymphocytes in this disease. We performed combined single-cell RNA sequencing and single-cell TCR sequencing in order to profile T cell repertoires in 10 patients with DADA2. Although there were no significant alterations of T cell subsets, we observed activation of both CD8+ and CD4+ T cells. There was no clonal expansion of T cells: most TCRs were expressed at basal levels in patients and healthy donors. TCR usage was private to individual patients and not disease specific, indicating as unlikely a common pathogenic background or predisposition to a common pathogen. We recognized activation of IFN pathways as a signature of T cells and STAT1 as a hub gene in the gene network of T cell activation and cytotoxicity. Overall, T cells in DADA2 patients showed distinct cell-cell interactions with monocytes, as compared with healthy donors, and many of these ligand-receptor interactions likely drove up-regulation of STAT1 in both T cells and other immune cells in patients. Our analysis reveals previously undercharacterized cell characteristics in DADA2.

Comprehensive analysis of ADA2 genetic variants and estimation of carrier frequency driven by a function-based approach.

BACKGROUND: Deficiency of adenosine deaminase 2 (DADA2) is an autoinflammatory disease caused by deleterious ADA2 variants. The frequency of these variants in the general population, and hence the expected disease prevalence, remain unknown. OBJECTIVE: We aimed to characterize the functional impact and carrier frequency of ADA2 variants. METHODS: We performed functional studies and in silico analysis on 163 ADA2 variants, including DADA2-associated variants and population variants identified in the Genome Aggregation Database. We estimated the carrier rate using the aggregate frequency of deleterious variants. RESULTS: Functional studies of ADA2 variants revealed that 77 (91%) of 85 of DADA2-associated variants reduced ADA2 enzymatic function by >75%. Analysis of 100 ADA2 variants in the database showed a full spectrum of impact on ADA2 function, rather than a dichotomy of benign versus deleterious variants. We found several in silico algorithms that effectively predicted the impact of ADA2 variants with high sensitivity and specificity, and confirmed a correlation between the residual function of ADA2 variants in vitro and the plasma ADA2 activity of individuals carrying these variants (n = 45; r = 0.649; P < .0001). Using <25% residual enzymatic activity as the cutoff to define potential pathogenicity, integration of our results with the database population data revealed an estimated carrier frequency of at least 1 in 236 individuals, corresponding to an expected DADA2 disease prevalence of ~1 in 222,000 individuals. CONCLUSIONS: Functional annotation guides the interpretation of ADA2 variants to create a framework that enables estimation of DADA2 carrier frequency and disease prevalence.