Background: Haploinsuffiency A20 (HA20) was first described in 2016 and is caused by a mutation in TNFAIP3/A20. Non-related families living on different continents were examined with whole exome sequencing (WES). All had symptoms of Behçet's disease. An autosomal dominant mutation was found.
Case presentation: When in her early teens, the patient had presented with a painful labial ulcer. She also had recurrent mouth ulcers, sometimes accompanied by fever and elevated CRP, and on occasion by abdominal pain. The ulcers were biopsied, and she was diagnosed with likely Behçet's disease. Some family members were later admitted with similar symptoms, and a genetic cause was suspected. Twenty years later a new genetic test was performed, and a revised diagnosis of HA20 was correctly made.
Interpretation: HA20 is a newly identified autoinflammatory disease due to an inherited mutation. This leads to increased production of pro-inflammatory cytokines such as IL-1, IL-6 and TNF α. The disease-causing process in this monogenic, inherited disease is very similar to the immune process in the acquired, multifactorial Behçet's disease. Fever, young age, abdominal involvement and global occurrence are factors that could lead to suspicion of HA20.