[A20 haploinsufficiency: what do clinicians need to know?]

A20 Haploinsufficiency (HA20) is a monogenic autoinflammatory disease associated with an autosomal dominant mutation in the TNFAIP3 gene. It induces a defect in the inactivation of the pro-inflammatory NF-κB pathway. Less than 200 cases have been described worldwide. The clinical picture of the disease is essentially based on the association of recurrent fever and/or biologic inflammatory syndrome, aphtosis, often bipolar, and cutaneous folliculitis. However, the clinical spectrum of HA20 is very broad, including gastrointestinal (mainly colonic ulceration), articular, cutaneous, pericardial and lymph node involvement, as well as frequent association with organ-specific or non-specific autoimmune manifestations and/or autoantibodies, including antinuclear antibodies and anti-dsDNA. As a result, the diagnosis of a number of systemic or organic disorders, most notably Behçet's disease, Crohn's disease, and sometimes even systemic lupus, has been corrected to HA20 by molecular research for a heterozygous mutation with functional deficiency of TNFAIP3. Although the first signs of the disease often appear in the first years of life, the diagnosis is often made in adulthood and requires the involvement of both paediatric and adult physicians. Treatment for HA20 is not codified and relies on conventional or biological immunomodulators and immunosuppressants adapted to the patient's symptomatology. This review highlights the enormous diagnostic challenges in this autoinflammatory disease.