Vasculopathy, Immunodeficiency, and Bone Marrow Failure: The Intriguing Syndrome Caused by Deficiency of Adenosine Deaminase 2

Clusters in Pediatric Rheumatic Diseases

PURPOSE OF THE REVIEW

Rheumatic diseases usually have very diverse and complex pathophysiology resulting in different clinical phenotypes. Some certain phenotypes cluster together with a common presentation, course, and outcome. Our primary aim is to review the known disease clusters in certain rheumatological conditions.

RECENT FINDINGS

Cluster analysis has been reported in several rheumatic diseases, Behcet disease being the most common. Five individual clusters together with some clinical associations have been reported in Behcet patients. Certain antibody-phenotype associations and damage clusters have been reported in systemic lupus erythematosus (SLE) patients as well. Although there is no proper cluster analysis, two distinct phenotypes are evident in deficiency of ADA2 (DADA2): those with a polyarteritis nodosa-like vasculopathy and hematological involvement with pure red cell aplasia or bone marrow failure. The variants are claimed to be different regions of this gene for these 2 phenotypes. Lastly, there is a recent paper grouping ANCA-associated vasculitis according to disease phenotype and antibody associations. There are distinct clusters in certain rheumatic diseases which might help us to predict comorbidities, disease course, and treatment response.

Genotype and functional correlates of disease phenotype in deficiency of adenosine deaminase 2 (DADA2)

BACKGROUND

Deficiency of adenosine deaminase 2 (DADA2) is a syndrome with pleiotropic manifestations including vasculitis and hematologic compromise. A systematic definition of the relationship between adenosine deaminase 2 (ADA2) mutations and clinical phenotype remains unavailable.

OBJECTIVE

We sought to test whether the impact of ADA2 mutations on enzyme function correlates with clinical presentation.

METHODS

Patients with DADA2 with severe hematologic manifestations were compared with vasculitis-predominant patients. Enzymatic activity was assessed using expression constructs reflecting all 53 missense, nonsense, insertion, and deletion genotypes from 152 patients across the DADA2 spectrum.

RESULTS

We identified patients with DADA2 presenting with pure red cell aplasia (n = 5) or bone marrow failure (BMF, n = 10) syndrome. Most patients did not exhibit features of vasculitis. Recurrent infection, hepatosplenomegaly, and gingivitis were common in patients with BMF, of whom half died from infection. Unlike patients with DADA2 with vasculitis, patients with pure red cell aplasia and BMF proved largely refractory to TNF inhibitors. ADA2 variants associated with vasculitis predominantly reflected missense mutations with at least 3% residual enzymatic activity. In contrast, pure red cell aplasia and BMF were associated with missense mutations with minimal residual enzyme activity, nonsense variants, and insertions/deletions resulting in complete loss of function.

CONCLUSIONS

Functional interrogation of ADA2 mutations reveals an association of subtotal function loss with vasculitis, typically responsive to TNF blockade, whereas more extensive loss is observed in hematologic disease, which may be refractory to treatment. These findings establish a genotype-phenotype spectrum in DADA2.

ADA2 Deficiency: Case Series of Five Patients with Varying Phenotypes

OBJECTIVE

To describe the clinical features, genotype, and treatment approaches of patients with confirmed adenosine deaminase 2 (ADA2) deficiency with dissimilar phenotypes.

METHODS

A case series of five DADA2 patients from three families was presented. The clinical and laboratory data, treatment protocols, and outcome of the patients were recorded from the patients' medical charts. ADA2 gene was screened by next generation sequencing first and then verified by Sanger sequencing. Serum ADA2 enzyme activity was measured by modified spectrophotometric method.

RESULTS

The median (min-max) age at onset of symptoms and age at diagnosis were 11 (9-13.8) years and 15 (9-19) years, respectively. The median (min-max) follow-up period was 8 (6-45) months. There was consanguinity in two families (2/3). The main clinical manifestations are musculoskeletal (5/5), dermatological (4/5), and neurological (2/5). Homozygosity for the p.G47R mutation in ADA2 gene was detected in three patients. A homozygous mutation in ADA2 gene (c.650 T > A; p.Val217Asp) was detected in two siblings. Plasma ADA2 enzymatic activity was absent in all patients. Anti-tumor necrosis factor (TNF) therapy was commenced, and all patients became clinically inactive with normal acute-phase reactants.

CONCLUSION

ADA2 mutations should be checked in patients with presence of inflammation and livedoid vasculitis when they have neurological findings, especially in the form of stroke; and a history suggesting for an inherited disease; or presence of resistance to conventional treatment. Besides, anti-TNF seems to be useful for treatment of DADA2.

ADA2 deficiency in a patient with Noonan syndrome-like disorder with loose anagen hair: The co-occurrence of two rare syndromes

Noonan syndrome-like disorder with loose anagen hair (NS/LAH) is one of the RASopathies, a group of clinically related developmental disorders caused by germline mutations in genes that encode components acting in the RAS/MAPK pathway. Among RASopathies, NS/LAH (OMIM 607721) is an extremely rare, multiple anomaly syndrome characterized by dysmorphic facial features similar to those observed in Noonan syndrome along with some distinctive ectodermal findings including easily pluckable, sparse, thin, and slow-growing hair. ADA2 deficiency (DADA2, OMIM 615688) is a monogenic autoinflammatory disorder caused by homozygous or compound heterozygous mutations in ADA2, with clinical features including recurrent fever, livedo racemosa, hepatosplenomegaly, and strokes as well as immune dysregulation. This is the first report of NS/LAH and ADA2 deficiency in the same individual. We report on a patient presenting with facial features, recurrent infections and ectodermal findings in whom both the clinical and molecular diagnoses of NS/LAH and ADA2 deficiency were established, respectively.