Expanding spectrum of DADA2: a review of phenotypes, genetics, pathogenesis and treatment.

Deficiency of adenosine deaminase 2 (DADA2) is a monogenic disease caused by biallelic mutations in ADA2 gene (previously CECR1). The aim of this review was to describe the clinical phenotypes, genetics, pathogenesis and treatment of DADA2. ADA2 is highly expressed on myeloid cells and deficiency leads to polarisation of macrophages to an M1 inflammatory type and activation of neutrophils. The pathogenesis of immunological and haematological manifestations is less clear. The spectrum of clinical presentations varies widely from asymptomatic individual to severe vasculitis, several autoinflammatory, immunological and haematological manifestations. Initially considered a childhood disease, the first presentation is now being reported well into adulthood. Vasculitis closely resembles polyarteritis nodosa. Livedoid reticularis/racemosa like skin rash and central nervous system involvement in the form of ischemic or haemorrhagic stroke are dominant manifestations. Immunological manifestations include hypogammaglobulinemia and recurrent infections. Lymphopenia is the most common haematological manifestation; pure red cell aplasia and bone marrow failure has been reported in severe cases. The disease is extremely heterogeneous with variable severity noted in patients with the same mutation and even within family members. Tumour necrosis factor inhibitors are currently the treatment of choice for vasculitic and inflammatory manifestations and also prevent strokes. Haematopoietic stem cell transplantation is a curative option for severe haematological manifestations like pure red cell aplasia, bone marrow failure and immunodeficiency. Further research is required to understand pathogenesis and all clinical aspects of this disease to enable early diagnosis and prompt treatment. Key Points • Deficiency of adenosine deaminase 2 (DADA2) is a monogenic disease caused by biallelic mutations in ADA2 gene. • The clinical features include vasculitis resembling polyarteritis nodosa, autoinflammation, haematological manifestations and immunodeficiency. • The severity varies widely from mild to fatal even in patients within a family and with the same mutation. • The treatment of choice for inflammatory and vasculitic disease is tumour necrosis factor α blockers. Bone marrow transplant may be considered for severe haematological disease.