Medical Genetics

Understanding A20 Haploinsufficiency (HA20)

At a Glance

A20 haploinsufficiency (HA20) is a rare genetic condition caused by a TNFAIP3 gene change that weakens the body’s control of inflammation. It can cause recurrent fevers, painful ulcers, bowel symptoms, arthritis, and rashes, while genetic testing confirms the diagnosis and symptoms vary widely.

Receiving a diagnosis of A20 Haploinsufficiency (HA20)—also known as TNFAIP3 deficiency—can feel overwhelming, especially given how rare this condition is. Published series indicate fewer than 200 cases have been reported worldwide, though exact numbers depend on how cases are counted ^[1]^[2]. For many patients and parents, the diagnosis follows years of searching for answers to unexplained fevers or painful ulcers ^[3]. While the news may bring a sense of relief that the symptoms finally have a name, it also marks the beginning of a new journey in managing a lifelong genetic condition.

What is HA20?

HA20 is primarily an autoinflammatory disease, meaning the innate immune system becomes dysregulated and inappropriately activated; autoimmune features (like certain autoantibodies) can occur in some patients, but they are not the core definition of the disease ^[3]. Under normal circumstances, the body produces a protein called A20 (encoded by the TNFAIP3 gene). This protein acts like a “brake” on the immune system, regulating inflammation once it is no longer needed ^[4]^[5].

In people with HA20, a pathogenic variant in the TNFAIP3 gene reduces or impairs this A20 regulation, meaning the body stays in a state of high alert, leading to episodes of inflammation ^[5].

The Journey to Diagnosis

The symptoms of HA20 usually begin in early childhood, with a median age of onset around 3.3 years in reported cohorts, though some individuals may not be diagnosed until adolescence or adulthood ^[1]. Because the symptoms clinically overlap with many other illnesses, substantial delays between first symptoms and a final genetic diagnosis are common ^[3].

Diagnosis is confirmed through clinical context and genetic testing that identifies a pathogenic variant (a disease-causing change) in the TNFAIP3 gene ^[6]. If standard sequencing does not find a change but doctors still strongly suspect HA20, they may perform specialized tests to look for deletions, where a small piece of the genetic code is missing entirely ^[7].

How HA20 Affects the Body

HA20 is a highly variable condition; no two people will have the exact same experience, even if they are in the same family ^[8]. The disease often follows a relapsing-remitting course, though persistent inflammation can also occur ^[1].

Common symptoms include:

Recurrent fevers: High temperatures that are driven by the dysregulated immune system ^[1]. Important Warning: A person with HA20 can also have an infection, and treatment with immune-modifying drugs can increase infection risk. Do not assume every fever is just a flare. Follow a clinician-specific fever plan, especially if the person appears ill.
Mucocutaneous ulcers: Painful sores in the mouth (oral ulcers) or, less commonly, in the genital area ^[3].
Gastrointestinal issues: Abdominal pain, diarrhea, or inflammation in the gut that can look like IBD (Inflammatory Bowel Disease) ^[3]^[1].
Joint and skin issues: Swollen, painful joints (arthritis) or various types of skin rashes ^[1].

Family and Inheritance

HA20 follows an autosomal dominant inheritance pattern.

Familial Cases: In many families, the gene is passed down from a parent. If a parent carries the variant, there is a 50% chance of passing the genetic variant to each child ^[9]. However, inheriting the variant does not guarantee clinically significant disease because penetrance and severity are highly variable.
De Novo Cases: In some people, the genetic change is “de novo,” meaning it started with them and was not inherited from either parent ^[10].
Variable Expressivity: Even when family members share the same genetic change, their symptoms can be very different. One person might have severe symptoms as a toddler, while a relative might have only occasional mouth sores or no symptoms at all ^[11]^[12].

Because of this variation, family testing should be coordinated through genetics professionals ^[13]^[8].

Life with a Rare Diagnosis

Navigating life with a rare condition like HA20 is a significant undertaking. Patients and parents often report high levels of stress and a sense of isolation ^[14]^[15]. The practical demands can involve frequent specialist visits and coordinating with schools or workplaces ^[16]^[17]. Connecting with rare disease communities and seeking support from a social worker or psychologist can be vital steps in navigating this new reality ^[18]^[19].

Common questions in this guide

What is A20 haploinsufficiency?

HA20 is a rare autoinflammatory disease caused by a disease-causing change in the TNFAIP3 gene. The change reduces the function of A20, a protein that normally helps turn off inflammation, so episodes of inflammation can occur.

What symptoms are common in HA20?

HA20 may cause recurrent fevers, painful mouth or genital ulcers, abdominal pain, diarrhea or bowel inflammation, arthritis, and skin rashes. Symptoms vary widely, and some people have persistent inflammation rather than clearly separated flares.

How do doctors confirm HA20?

Diagnosis combines the pattern of symptoms with genetic testing for a pathogenic TNFAIP3 variant. If routine sequencing is negative but HA20 remains likely, additional testing may look for a deletion or another missing piece of the gene.

Can HA20 be passed from a parent to a child?

Yes. HA20 is usually inherited in an autosomal dominant pattern, so a parent with the variant has a 50% chance of passing it to each child, although symptoms can differ greatly. Some cases arise de novo, meaning the change was not inherited from either parent, and family testing should be guided by a genetics professional.

Is every fever in someone with HA20 a flare?

No. A person with HA20 can also have an infection, and immune-modifying medicines can increase infection risk. Follow the clinician-provided fever plan and seek medical guidance promptly if the person appears ill.

What support may help a person or family living with HA20?

HA20 can require ongoing specialist visits, school or workplace coordination, and planning for flares. Rare-disease communities and support from a social worker or psychologist may help with stress, isolation, and practical needs.

Get notified when new evidence is published on A20 haploinsufficiency.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.

References (19)

1
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11
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This page is for informational purposes only and does not constitute medical advice about A20 haploinsufficiency. A genetics professional and treating clinician should interpret test results and create an individualized fever and flare plan.