To describe the clinical, biological and genetic characteristics of paediatric-onset A20 haploinsufficiency (HA20) and to identify key clinical features that may guide early diagnosis and management. Multicentre, retrospective observational cohort study through the French national paediatric rheumatology network and national reference laboratories for genetic autoinflammatory diseases. 17 patients from 11 unrelated families, with disease onset before 18 years of age and carrying a tumour necrosis factor alpha-induced protein 3 (TNFAIP3) mutation, were included. Median age at symptom onset was 3 years (range: 1 month-17 years) with a median diagnostic delay of 9.7 years (range: 1-43 years). Boys had a significantly earlier onset and diagnosis than girls. The most common initial manifestations were oral ulcers (64.7%), fever (64.7%), abdominal pain (47.1%), arthralgia (35.3%) and skin eruption (17.6%). Genital ulcers occurred in 17.6% at onset but in 52.9% during follow-up. Gastrointestinal involvement was frequent (abdominal pain in 76.5% of patients and colitis in 35.3%). Other features included arthralgia (52.9%), arthritis (29.4%), skin eruption (41.2%), lymphadenopathy (35.3%), hepatomegaly (11.8%), headache (17.6%) and uveitis (5.9%). C reactive protein (CRP) levels were significantly higher during flares. Three novel TNFAIP3 variants were identified. Colchicine was effective as monotherapy in 40%. TNF-inhibitors showed the highest efficacy (adalimumab 60%, infliximab 100%). HA20 should be suspected in children with fever and gastrointestinal inflammation, even in the absence of oral/genital ulcers. Early onset colitis, the distinctive morphology of mucosal ulcers and a positive family history for HA20 are particularly suggestive. Early genetic testing may enable prompt diagnosis and targeted therapy.

Behçet's disease (BD) is a chronic inflammatory disorder characterized by recurrent oral aphthous ulcers, genital ulcers, skin lesions, and uveitis. Recent genetic studies have identified monogenic diseases with phenotypes resembling BD, including RELA-associated inflammatory disease (RAID), Haploinsufficiency of A20 (HA20), and otulipenia. The RelA gene encodes the RELA protein, which is involved in the nuclear factor kappa B (NF-κB) signaling pathway that regulates the transcription of genes associated with cell survival, apoptosis, and immune responses. In RAID, dysfunction of the NF-κB pathway leads to reduced cell survival and symptoms of BD, such as recurrent fever, chronic mucocutaneous ulceration, arthralgia, and colitis. Herein, we report a pediatric patient who presented with recurrent, severe oral and genital ulcers from the age of five years and was diagnosed with RAID following a documented RelA gene mutation. The patient responded to a combination of corticosteroids, colchicine and methotrexate. RAID should be considered in the differential diagnosis of patients with early onset recurrent fever and mucosal ulcerations.

Monogenic autoinflammatory uveitis belongs to the spectrum of monogenic autoinflammatory diseases. When early-onset uveitis is associated with specific extra-ocular manifestations, particularly in a familial or geographical context, it guides the clinician towards a diagnosis of a monogenic autoinflammatory disease. The clinical presentation and mode of inheritance will help identify the underlying cause, and the detection of a pathogenic variant will confirm the diagnosis and guide the management approach. In this review, we outline the main monogenic autoinflammatory uveitis conditions that clinicians should be aware of: Blau syndrome, ROSAH syndrome, cryopyrin-associated periodic syndromes (CAPS), partial mevalonate kinase deficiency, A20 haploinsufficiency, and NEMO syndrome.

A20 haploinsufficiency (HA20) is an early-onset autoinflammatory disease caused by loss-of-function variants of the TNFAIP3 gene, which encodes the protein A20. HA20 is typically characterized by Behçet's disease-like clinical symptoms, and patients usually present with a family history. Herein, we report a case of HA20 in a pediatric patient, presenting with periodic fever, abdominal pain, and vomiting, with no family history. This patient also harbored a novel heterozygous frameshift variant c.677del (p.Pro226LeufsTer2) of TNFAIP3. We initiated treatment with an anti-tumor necrosis factor-α agent that did not induce symptom resolution; we thus administered combination therapy, including prednisolone. Remission was then successfully achieved. We suggest that HA20 should be considered when an autoinflammatory disease is suspected and periodic fever syndrome is present, even in the absence of a family history of HA20 or Behçet's disease-like symptoms.

Autoinflammatory diseases are systemic disorders caused by genetic or acquired abnormalities in certain signaling pathways of the innate immune system. Dysregulated activation of the inflammasome, i.e. molecular platforms responsible for the activation of caspase-1 and production of interleukin-1β, causes autoinflammation. Familial Mediterranean fever (FMF), the most common genetic autoinflammatory disease, is characterized by a periodic fever and serositis. The complex and heterogeneous genetic background of Japanese FMF patients, accompanied by potential overlap with other rheumatic diseases, suggests crosstalk between genetic and environmental factors. Recently, FMF has been recognized as being part of a spectrum of autoinflammatory syndromes named pyrin-associated autoinflammatory diseases. The discovery of a new monogenic autoinflammatory disease, A20 haploinsufficiency, may provide novel insights into early-onset Behçet's-like diseases. In contrast, adult-onset Still's disease and Schnitzler's syndrome are acquired autoinflammatory diseases without a monogenic abnormality. Although the concept of autoinflammatory diseases originally applied to monogenic hereditary recurrent fevers, it has been expanded to include non-genetic complex autoinflammatory diseases. Information concerning monogenic autoinflammatory diseases may prove useful for elucidating the molecular mechanisms underlying non-genetic autoinflammatory diseases.