Deficiency of adenosine deaminase 2 (DADA2): Review

Infantile Pure Red Cell Aplasia Secondary to Deficiency of Adenosine Deaminase2 (DADA2) Syndrome-Time to Think Beyond Diamond Blackfan Anemia

Deficiency of adenosine deaminase 2 (DADA2) is a rare autosomal recessive disorder characterized by vasculopathy, immunodeficiency, and hematological abnormalities. Its presentation as infantile pure red cell aplasia (PRCA) often mimics Diamond Blackfan anemia (DBA), leading to diagnostic delays and suboptimal management. This study retrospectively analyzed nine cases of DADA2-related PRCA diagnosed over 5 years at a tertiary care hospital. All patients harbored homozygous ADA2 mutations, predominantly p.Ile93Thr, and presented with severe anemia and reticulocytopenia. Misdiagnosed initially as DBA, none responded to steroid therapy. Our findings emphasize the need for comprehensive genetic analysis in PRCA to distinguish DADA2 from DBA for appropriate treatment.

Sex differences in adenosine deaminase activity associate with disparities in SARS-CoV-2 innate immunity

Females demonstrate elevated type-I interferon production and a stronger antiviral immune response; however, the mechanisms underlying sex-based differences in antiviral immunity are incompletely understood. We previously reported that low adenosine deaminase (ADA) activity perturbs the methylation-based transcriptional silencing of endogenous retroviral elements (hERV), which stimulates IFN-Stimulated Genes (ISG) and primes antiviral immunity. Here we demonstrate lower ADA activity in females compared to their male counterparts, which correlated with higher hERV and ISG expression in female lungs. Sex differences in ADA2 were linked to the number and expression profiles of blood and lung-derived monocyte populations. Single-cell RNA sequencing of respiratory cells from patients with COVID-19 showed a significant female bias in hERV-ISG signatures, and implicated IL-18 as a driver of sex-specific ADA2 expression. Observations in healthy and COVID-19 cohorts indicate that higher ADA activity is associated with suppressed antiviral innate immunity in the male respiratory tract, which may drive adverse COVID-19 outcomes.

Adenosine deaminase and deoxyadenosine regulate intracellular immune response in C. elegans

Adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) are enzymes in the purine salvage pathway, which recycles purines to meet cellular demands. Mutations of these enzymes in humans cause inflammatory and immunodeficiency syndromes, but the mechanisms are not well understood. Prior work in the nematode Caenorhabditis elegans demonstrated that loss of PNP ortholog PNP-1 induced an immune response called the intracellular pathogen response (IPR). Here, we show that loss of the enzyme upstream of PNP-1 called ADAH-1 (ADA homolog) also induces the IPR and promotes resistance against intracellular pathogens. Unlike PNP-1, ADAH-1 is essential for organismal development. Importantly, we find that supplementation of deoxyadenosine, a substrate for ADA, induces the IPR and promotes resistance to intracellular pathogens in C. elegans, a finding we extend to human cells. Thus, mutations in ADA and PNP induce innate immunity through increased deoxyadenosine, a phenomenon that is conserved from C. elegans to humans.

Bilateral cataracts in a three-year-old with deficiency of adenosine deaminase 2 (DADA2), hyperferritinemia, and prolonged steroid use

BACKGROUND

Deficiency of adenosine deaminase 2 (DADA2) is a rare autosomal recessive autoinflammatory disorder associated with systemic vasculitis and bone marrow failure. Reported ophthalmic findings in DADA2 include optic neuritis, retinal artery occlusion, uveitis, and optic atrophy. We report the case of a child found to have bilateral cataracts.

CASE REPORT

A three-year-old recent immigrant from Mexico with a diagnosis of DADA2 and transfusion-dependent anemia was referred to ophthalmology to screen for deferasirox-associated retinopathy in the setting of hemochromatosis. He was incidentally found to have bilateral posterior subcapsular cataracts with no other ophthalmic abnormalities. The child's lab findings were significant for chronic hyperferritinemia, and his history was significant for over a year of oral prednisone use in Mexico.

CONCLUSIONS

This is the first reported case of cataracts in a child with DADA2. While DADA2 is an autoinflammatory disorder, this child's lack of uveitis suggests a non-inflammatory etiology. Hyperferritinemia is a known cause of cataracts and is common in DADA2, but the child's history of oral steroid use in Mexico could also explain his cataracts. As pediatric cataracts have not otherwise been reported in DADA2, ophthalmologists should be aware of this possibility, especially in children with hyperferritinemia or a history of steroid use.

Mimics and challenging presentations of DADA2

Deficiency of adenosine deaminase 2 (DADA2) has been a challenging diagnosis to make since it was first described in 2014. The disease represents a wide range of phenotypes. Therefore, it may present with various clinical patterns. Throughout the years, several difficult-to-diagnose cases of DADA2 were reported in the literature. Although several studies and reviews were published regarding different phenotypes and manifestations of DADA2, a review of challenging cases with diverse combinations of DADA2 manifestations was needed to integrate the knowledge from the literature into the clinical practice. Immunological, hematologic, autoinflammatory, and adult-onset polyarteritis-nodosa patterns were reported in the literature as cases challenging to diagnose. In this review, we aim to summarize the challenging case reports from the literature, provide an algorithmic approach for these kinds of presentations, and share our perspective and recommendations on the topic. Diagnosing DADA2 on time is a vital issue for preventing fatal and debilitating vascular events with anti-TNF-alpha therapy. Thus, early testing for DADA2 in suspected cases is recommended. Family history and genetic testing of the patient and the first-degree relatives are essential for accurate diagnosis. Thorough systemic examination and imaging might help detect clinically silent findings of vasculitis. Enzymatic activity of ADA2, when available, is also a key diagnostic tool that complements genetic testing and clinical evaluation.

Polyarteritis nodosa mimics Kawasaki disease

Polyarteritis nodosa (PAN) is a rarely seen vasculitis that often affects small-sized and medium-sized arteries. PAN can present with diverse clinical features depending on the organs involved, including potential cardiac involvement. Typical cardiac manifestations of PAN in the paediatric age group include pericarditis, valvular heart disease and coronary artery aneurysms. In contrast to PAN, Kawasaki disease (KD) is often associated with coronary artery abnormalities. Herein, we report a case of a young boy presented with KD-like features, including a coronary artery aneurysm confirmed by an echocardiogram (ECHO) and eventually diagnosed as PAN. The patient was treated with steroids, methotrexate and tocilizumab with improvement of the symptoms. Repeated ECHO revealed the resolution of the coronary artery aneurysms. Our paper highlights a rare presentation of PAN mimicking KD presentation. Physicians should consider PAN in chronic or severe courses of KD or coronary artery aneurysms.

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.

Polyarteritis nodosa complicated by renal aneurysm and intestinal perforation: A case report

RATIONALE

Polyarteritis nodosa (PAN) is a necrotizing vasculitis that affects small- and medium-sized arteries, presenting with diverse clinical manifestations. It can impact tissues and organs throughout the body and may be life-threatening in severe cases. Common causes of death include cardiac, renal, and gastrointestinal complications or aneurysm rupture. While separate reports of renal aneurysm and intestinal perforation exist, the coexistence of these conditions is rarely documented. This study reports a severe case of PAN complicated by both renal aneurysm and intestinal perforation, aiming to deepen the understanding of this disease, aid in clinical diagnosis and treatment, and improve patient prognosis.

PATIENT CONCERNS

The patient presented to the hospital with dorsal foot pain and abdominal pain persisting for more than 4 months, along with pain and discomfort in both lower extremities for over 1 month.

INTERVENTIONS

The patient was diagnosed with PAN, renal aneurysm, intestinal perforation, and grade 3 hypertension (high risk).

OUTCOMES

After treatment, the patient showed normal temperature and blood pressure, relief from abdominal pain, and disappearance of myalgia and numbness in the lower limbs. Additionally, the renal aneurysm shrank significantly, the intestinal perforation healed, the ileostomy was reduced, and the patient's condition stabilized.

LESSONS

The clinical symptoms of PAN mostly lack specificity, and should be distinguished from microscopic polyangiitis and simulated vasculitis. For patients with intestinal perforation similar to this case, tocilizumab treatment may be effective, but further research is needed to confirm it.

Central retinal artery occlusion in a child with ADA2 deficiency: a case report

Introduction and importance

Deficiency of ADA2 (DADA2) is the first molecularly described monogenic vasculitis syndrome. During the past decade, DADA2's clinical spectrum has expanded significantly as the number of reported cases has increased.

Case presentation

A 5-year-old boy with DADA2 who experienced sudden onset left-sided vision loss due to unilateral central retinal artery occlusion. The patient had a history of recurrent fever and arthralgia with high inflammatory markers (C-reactive protein and erythrocyte sedimentation rate). Brain MRI showed mild limbic encephalitis, and MRA was normal. His gene sequencing results demonstrated substitutions mutation in ADA2, and the diagnosis of DADA2 was eventually confirmed.

Clinical discussion

Central retinal artery occlusion (CRAO) in paediatrics is a very rare condition. Typically, DADA2 presents in childhood as systemic inflammation, vasculitis, humoral immunodeficiency, and/or haematologic abnormalities. The most common phenotype described in the literature is vasculitis, which typically affects the skin and central nervous system, but other systems can also be affected. Ophthalmic manifestations are less common and highly variable.

Conclusions

DADA2 manifests rarely with central retinal artery occlusion; therefore, physicians should be aware of this manifestation.