A20 Haploinsufficiency (HA20): A Patient Guide

A20 Haploinsufficiency (HA20), also known as TNFAIP3 deficiency, is an exceptionally rare genetic condition that causes the innate immune system to become dysregulated, leading to episodic or persistent inflammation. While most people with HA20 begin showing symptoms early in childhood, it can affect individuals into adolescence and adulthood, often presenting with recurrent high fevers, painful mouth and genital ulcers, and significant gastrointestinal or joint pain ^[1]. Because these symptoms overlap with other autoinflammatory or autoimmune diseases, published series have reported substantial delays before a definitive genetic diagnosis is reached ^[2].

At the biological level, HA20 is caused by a missing ‘brake’ in the body’s inflammatory response. Normally, the TNFAIP3 gene produces a protein called A20, which functions to turn off the NF-κB pathway once an infection has been cleared ^[3]. In people with HA20, a pathogenic variant in this gene reduces or impairs A20 regulation ^[4]. Without this crucial regulator, innate immune signaling is inappropriately activated, leading to the wide range of symptoms that affect the skin, gut, and joints ^[5].

Living with HA20 requires a coordinated, longitudinal approach to care. Because the condition is autosomal dominant, it can be passed from a parent to a child, making genetic counseling an essential step for the entire family ^[6]. Treatment is highly personalized and often off-label, focusing on controlling fever and organ inflammation through a combination of traditional medications and targeted therapies that block specific inflammatory signals ^[7]. While HA20 is a lifelong genetic predisposition, symptoms can vary widely, and active medical management allows many patients to reach a state of low disease activity where they can thrive and participate fully in daily life ^[1][6].