Adenosine Deaminase 2 Deficiency

Systemic Autoinflammatory Disease

Clinical findings

• Intermittent fevers
• Hepatosplenomegaly (can be evidence of portal hypertension)
• Systemic hypertension

Laboratory findings

• Elevated C-reactive protein (CRP) and erythrocyte sedimentation rate during flare episodes
• Elevated transaminases

Vasculitis

Clinical findings

• Onset. Usually in early childhood (i.e., age <10 years)
• Skin. Livedo racemosa/reticularis and/or polyarteritis nodosa and/or undifferentiated skin rash
• Neurologic. Early-onset lacunar and/or hemorrhagic strokes

Laboratory findings. Absence of antineutrophilic cytoplasmic antibodies (ANCA)

Imaging findings

• MRI
  • Acute or chronic lacunar ischemic infarcts located in the deep-brain nuclei and/or the brain stem and sparing the subcortical white matter
  • Hemorrhagic stroke and intracranial bleeding
• Angiography. Aneurysm or stenosis in medium-sized arteries

Dysregulation of Immune Function

Clinical findings

• Immunodeficiency
• Lymphoproliferative disease including lymphadenopathy

Laboratory findings

• Hypogammaglobulinemia, with low levels of IgM, IgG, and/or IgA. Low serum immunoglobulin levels may correlate with inflammatory disease activity [Schepp et al 2017].
• Impaired production of transitional and switched memory B cells
• Low vaccine responses noted in some cases
• Although T cells are largely not affected, defective T-cell proliferation, mild-to-profound CD4+ lymphopenia, and low NK counts have been reported [Trotta et al 2018].
• Positive lupus anticoagulant (present in 41% of the Authors' cohort of 41 patients who were tested – in which ascertainment could be skewed in favor of individuals with inflammatory findings) [Author, unpublished data]

Hematologic Abnormalities

Hematologic disorders typically occur early in life; however, in rare instances bone marrow failure may initially appear as late as adulthood (i.e., 5th and 6th decades):

• Lymphopenia
• Neutropenia
• Pure red cell aplasia
• Thrombocytopenia
• Pancytopenia

Bone marrow biopsy may reveal hypo/hypercellularity, grade I myelofibrosis, lymphocyte infiltrate (predominantly CD8+), and mild reticulin fibrosis, further suggesting a defect in cell differentiation. In one individual the bone marrow showed a reduced number of CD138+ plasma cells [Zhou et al 2014, Van Eyck et al 2015, Ben-Ami et al 2016, Hashem et al 2017a, Michniacki et al 2018, Trotta et al 2018].

Other

Other clinical findings include musculoskeletal features, aphthous ulcers, inflammatory bowel disease-like illness, and hearing loss.

Other laboratory findings. In contrast to individuals with an inherited deficiency of ADA, persons with DADA2 do not have profound lymphopenia and their erythrocytes have normal levels of ADA activity and undetectable (rather than elevated) levels of deoxyadenosine triphosphate or total deoxyadenosine nucleotides.

Option 1

When the phenotypic and laboratory findings suggest the diagnosis of DADA2 molecular genetic testing approaches can include single-gene testing or use of a multigene panel. Among 66 individuals who were clinically suspected of having DADA2 and underwent genetic analysis at a French referral center for autoinflammatory disorders, 13 individuals from 11 families (20%) were found to have biallelic ADA2 pathogenic variants [Rama et al 2018]. Among those with DADA2, more than 80% had a combination of a biomarker of inflammation (fever, elevated CRP), evidence of vasculitis (cutaneous, neurologic), and more than one clinical flare. Of note, these criteria may not apply to individuals who present with hematologic manifestations only [Ben-Ami et al 2016, Sönmez et al 2018].

Single-gene testing. Sequence analysis of ADA2 detects biallelic, homozygous or compound heterozygous, missense, nonsense, and splice site variants; typically, exon or whole-gene deletions/duplications are not detected. In individuals with a highly suspicious clinical presentation and or/low plasma/serum ADA2 activity in whom only one or no pathogenic variant is found, performing gene-targeted deletion/duplication analysis may detect intragenic deletions or duplications (i.e., copy number variants).

A multigene panel that includes ADA2 and other genes associated with immune dysregulation, primary immunodeficiency, or autoinflammatory syndromes (see Differential Diagnosis) is most likely to identify a genetic cause at the most reasonable cost while limiting identification of variants of uncertain significance and pathogenic variants in genes that do not explain the underlying phenotype. Note: (1) The genes included in the panel and the diagnostic sensitivity of the testing used for each gene vary by laboratory and are likely to change over time. (2) Some multigene panels may include genes not associated with the condition discussed in this GeneReview. (3) Some laboratories offer custom-designed panels and/or phenotype-focused exome analysis that includes genes specified by the clinician. (4) Methods used in a panel may include sequence analysis, deletion/duplication analysis, and/or other non-sequencing-based tests. For diagnosis of DADA2 a multigene panel that also includes deletion/duplication analysis is recommended (see Table 1).

For an introduction to multigene panels click here. More detailed information for clinicians ordering genetic tests can be found here.

Option 2

When the diagnosis of DADA2 has not been considered because an individual has atypical phenotypic features, comprehensive genomic testing (which does not require the clinician to determine which gene[s] are likely involved) is the best option. Exome sequencing is most commonly used; genome sequencing is also possible. If exome sequencing identifies only one ADA2 pathogenic variant, perform exome array (when clinically available) to detect (multi)exon deletions or duplications that cannot be detected by sequence analysis.

For an introduction to comprehensive genomic testing click here. More detailed information for clinicians ordering genomic testing can be found here.

ADA2 enzyme activity. In humans, the enzyme ADA2 is present in plasma and myeloid cells, but not in erythrocytes. DADA2 is associated with low (<5% of normal) or absent ADA2 enzymatic activity in serum or plasma (fresh or stored frozen samples). DADA2 can also be diagnosed by measuring ADA2 activity in extracts of dried plasma spots on filter paper [Ben-Ami et al 2016]. The two biochemical assays used are ELISA (enzyme-linked immunosorbent assay) and HPLC (high-performance liquid chromatography).

Note: (1) An ELISA-based assay for ADA2 activity is commonly used in research laboratories but may not be available in clinical laboratories; (2) although deficiency of immuno-precipitable ADA2 enzyme has been demonstrated in persons with DADA2 [Zhou et al 2014], no anti-ADA2 antibody-based method has been validated for use in clinical laboratories.

Vasculitis

The most frequent manifestations of DADA2 are related to arterial vasculopathy which often manifests as cutaneous lesions. Cutaneous manifestations, reported in more than 75% of affected individuals, include livedo racemosa/reticularis, polyarteritis nodosa (PAN), subcutaneous nodules, cutaneous ulcers, or lupus-like rash [Gonzalez Santiago et al 2015, Caorsi et al 2016, Skrabl-Baumgartner et al 2017].

Histopathologic findings of DADA2-associated PAN and PAN of unknown cause are the same: non-granulomatous, necrotizing vasculitis of small and medium-sized vessels. Sometimes less specific findings are interpreted as leukocytoclastic vasculitis. In younger individuals with livedoid rash, skin biopsy shows interstitial neutrophil and macrophage infiltration without overt vasculitis.

In one study, nine (15%) of 60 children with PAN, cutaneous PAN, unclassifiable vasculitis (UCV), young-onset chronic vasculitis, or history of stroke were found to have biallleic ADA2 pathogenic variants. Previous clinical diagnoses included PAN (5 children), UCV (3), and ANCA-associated vasculitis (1) [Gibson et al 2019].

Ischemic strokes are often observed in (but not limited to) the brain stem, thalamus, basal ganglia, and internal capsule [Bulut et al 2019]. These small infarcts, described as lacunar strokes, may not always be observable on MRI.

Over time accumulation of the effects of these small initially undetectable strokes can lead to severe neurologic impairments such as persistent dysarthria, ataxia, palsy of one or more cranial nerves, and cognitive impairment [Springer et al 2018].

Other neurologic manifestations can include the following:

• Small, deep intracerebral hemorrhage. Specifically, hemorrhagic strokes were observed on MRI and/or CT in the ventricular system and right frontal insula in different individuals. Most often they occur in the setting of concomitant use of antiplatelet or anticoagulant therapy; however, on rare occasion they may occur spontaneously [Belot et al 2014, Garg et al 2014, Navon Elkan et al 2014, Zhou et al 2014, Nanthapisal et al 2016, Lee et al 2018].
• Cerebral vessel aneurysm (1 patient) [Navon Elkan et al 2014]
• Seizures resulting from strokes. Manifestations are related to the location of the stroke.
• Central and peripheral neuropathy. The diverse manifestations reported include cranial nerve palsies, sensorineural hearing loss, and ophthalmologic complications [Lee 2018].

Other effects of distal artery occlusion include peripheral vascular insufficiency, digital necrosis, and Raynaud phenomena [Navon Elkan et al 2014, Zhou et al 2014].

GI manifestations generally include abdominal pain and chronic gastritis. On rare occasions, intestinal necrosis, bowel perforation, and arterial stenosis are observed [Belot et al 2014, Batu et al 2015].

Hepatic disease involves hepatomegaly and splenomegaly that can lead to portal hypertension and associated esophageal varices. Histopathologic findings include evidence of nodular regenerative hyperplasia and/or hepatic sclerosis that can potentially lead to end-stage liver disease [Springer et al 2018].

Other organs with dense vascularization such as the kidney can be affected. Multiple aneurysmal dilatations and variation in the caliber of medium-small intrarenal arteries have been reported as well as renal artery stenosis and infarcts [Navon Elkan et al 2014, Nanthapisal et al 2016, Sahin et al 2018].

Dysregulation of Immune Function

General dysregulation of immune function can include immunodeficiency, lymphoproliferative disease, and autoimmune manifestations of varying severity.

Immunodeficiency. While the autoinflammatory phenotype was predominant in the initial description of DADA2, mild immunodeficiency was identified in five of nine patients in the cohort [Zhou et al 2014]. Intially it was not clear if immunodeficiency could be related to the use of immunosuppressive therapies; however, subsequently in the German cohort of 181 individuals with antibody deficiency and/or features of common variable immunodeficiency, eleven individuals were found to have DADA2 [Schepp et al 2016, Schepp et al 2017]; of these, four presented with immunodeficiency without vascular manifestations. To date the spectrum of immunodeficiency includes variable degrees of B-cell depletion and hypogammaglobulinemia. T-cell numbers are largely unaffected except in patients with bone marrow failure.

About 20% of individuals with DADA2 experience bacterial and/or viral infections resulting from immunodeficiency. Bacterial infections typicaly involve the upper- and lower-respiratory tract, gastrointestinal tract, and urinary tract. Viral infections have included recurrent herpes simplex infections, skin warts (caused by the human papilloma virus) [Arts et al 2018], and in one child, shingles (caused by the herpes zoster virus) [Ghurye et al 2019].

Although fungal and mycobacterial infections are unusual, they were observed in one individual with severe monocytopenia [Hsu et al 2016] and in two sibs with a contiguous gene deletion involving ADA2 and IL-17RA in whom recurrent fungal infections were attributed to IL-17R deficiency [Fellmann et al 2016].

Lymphoproliferative disease. Generalized lymphadenopathy is seen in more than 10% of affected individuals; splenomegaly is fairly common. The lymphoproliferative phenotype of DADA2 can include the following:

• Features mimicking the following disorders:
  • GATA2 deficiency [Hsu et al 2016]
  • Autoimmune lymphoproliferative syndrome (ALPS) [Alsultan et al 2018, Barzaghi et al 2019]
  • Multicentric Castleman disease [Van Nieuwenhove et al 2018]
• CD3+ CD8+ T-cell large granular lymphocytic (T-LGL) infiltration of the bone marrow (in 2 individuals) [Trotta et al 2018].
• Adolescent-onset Hodgkin's lymphoma (HL) was initialy reported in one individual (however, definitive supporting evidence for HL was not available) [Springer et al 2018]. More recently, childhood-onset HL was histopathologically confirmed in two sibs with DADA2 [Alabbas et al 2019].

Autoimmune disease resembling systemic lupus erythematosus and autoimmune cytopenia was reported in two unrelated families [Schepp et al 2016, Skrabl-Baumgartner et al 2017].

Hematologic Disease

Hematopoietic complications include variably decreased numbers of leukocytes, platelets, and erythrocytes (including pure red cell aplasia [PRCA] similar to Blackfan-Diamond anemia), as well as pancytopenia due to complete bone marrow failure. A meta-analysis of published data on 161 individuals with DADA2 revealed anemia in 13%, neutropenia in 7%, and thrombocytopenia in 6%, whereas leukopenia, PRCA, NK cell deficiency, and pancytopenia were observed in fewer than 5% [Meyts & Aksentijevich 2018].

The initial clinical presentation in five children from four unrelated consanguineous families was PRCA and hemolytic anemia without manifestations of inflammation or vasculitis [Ben-Ami et al 2016].

Neutropenia was severe (i.e., low or absent absolute neutrophil counts) in two affected individuals [Hashem et al 2017a, Cipe et al 2018] and moderate but persistent in other affected individuals [Ghurye et al 2019].

Musculoskeletal Manifestations

About 40% of affected individuals have the following musculoskeletal manifestations: myalgia/arthralgia (22%), arthritis (14%), and myositis (1%) [Meyts & Aksentijevich 2018, Sahin et al 2019]. Musculoskeletal manifestations are often accompanied by other features of systemic inflammation, such as fevers and/or elevated acute-phase reactants.

Current Treatment for Persons with Symptomatic DADA2

Anti-tumor necrosis factor (TNF) agents (also known as "biologics") including etanercept, adalimumab, golimumab, infliximab, and certolizumab are the drugs of choice to prevent and eliminate manifestations of autoinflammatory disease / vasculitis. Use of such drugs reduces risk of ischemic stroke and inflammatory burden (as shown by lower CRP/ESR levels and less skin rash) and relieves immunodeficiency, hepatosplenomegaly, and neutropenia. In a cohort of 15 patients with DADA2 who had a total of 37 strokes before the initiation of anti-TNF therapy, no strokes were observed post treatment [Ombrello et al 2019]. Use of such drugs also increases growth and development in affected children, and improves red blood cell and platelet counts due to relief of the inflammatory burden. Of note, anti-TNF agents appear to have little effect in rescuing severe bone marrow abnormalities.

Some individuals with low serum immunoglobulins and frequent infections may require treatment with intravenous immunoglobulin as well as antibiotics and antivirals in conjunction with anti-TNF agents [Hashem et al 2017c, Schepp et al 2017].

Methotrexate is added when administering adalimumab or infliximab to prevent development of drug-related antibodies.

Thalidomide is a potential treatment for TNF blockade when biologics are not available. Thalidomide is known to inhibit TNF production in dendritic cells and to exert an inhibitory effect on monocytes [Deng et al 2003]. Of note, in a study of six patients, all responded completely to thalidomide treatment; subsequently, however, the drug had to be discontinued (after treatment ranging from 20 months to 5 years) in three of the six due to neurologic toxicity [Caorsi et al 2017]. A study evaluating long-term thalidomide treatment in patients with multiple myeloma characterized neurologic toxicity as sensory peripheral neuropathy, including paraesthesias, tremor, and dizziness [Tosi et al 2005].

Steroids and general immunosuppressive therapies (e.g., azathioprine, cyclosporine, cyclophosphamide, methotrexate, mycophenolate mofetil, and tacrolimus) have had variable success.

Anti-IL-6 therapy was successfully used in a patient with DADA2 whose manifestations mimicked multicentric Castleman disease [Van Nieuwenhove et al 2018].

Hematopoietic stem cell transplantation (HSCT) can be curative in individuals in whom bone marrow failure and/or immune dysregulation predominate, and who fail to respond to TNF inhibitor treatment. Successful HSCT returns plasma ADA2 activity to normal levels. In one study the hematologic and immunologic phenotype resolved post HSCT in all 14 patients with bone marrow dysfunction or immunodeficiency (6 of whom also had vasculitis); however, acute and moderate chronic autoimmunity and graft-versus-host disease were reported [Hashem et al 2017c].

Current Treatment for Asymptomatic Persons with Biallelic DADA2-Causing Variants in ADA2

Currently there are no predictors of which individual with biallelic ADA2 pathogenic variants will develop a stroke or when a stroke may occur. Because of the potentially devastating consequences of stroke, the authors treat all individuals who have biallelic ADA2 pathogenic variants with anti-TNF agents to reduce the risk of stroke.