Adenosine deaminase 2 deficiency

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Adenosine deaminase 2 (ADA2) deficiency is a disorder characterized by abnormal inflammation of various tissues. Signs and symptoms can begin anytime from early childhood to adulthood. The severity of the disorder also varies, even among affected individuals in the same family.

Inflammation is a normal immune system response to injury and foreign invaders (such as bacteria). However, ADA2 deficiency causes abnormal, unprovoked inflammation that can damage the body's tissues and organs, particularly blood vessels. (Inflammation of blood vessels is known as vasculitis.) Other tissues affected by abnormal inflammation can include the skin, gastrointestinal system, liver, kidneys, and nervous system. Depending on the severity and location of the inflammation, the disorder can cause disability or be life-threatening.

Signs and symptoms that can occur with ADA2 deficiency include fevers that are intermittent, meaning they come and go; areas of net-like, mottled skin discoloration called livedo racemosa; an enlarged liver and spleen (hepatosplenomegaly); and recurrent strokes affecting structures deep in the brain that can start in the first few years of life. In some people, ADA2 deficiency causes additional immune system abnormalities that increase the risk of bacterial and viral infections.

ADA2 deficiency is sometimes described as a form of polyarteritis nodosa (PAN), a disorder that causes inflammation of blood vessels throughout the body (systemic vasculitis). However, not all researchers classify ADA2 deficiency as a type of PAN.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

ADA2 deficiency is caused by mutations in the ADA2 gene. This gene provides instructions for making an enzyme called adenosine deaminase 2. Studies suggest that this enzyme plays an essential role in the growth and development of certain immune system cells, including macrophages, which are a type of white blood cell that plays a critical role in inflammation. Some macrophages are pro-inflammatory, meaning they promote inflammation, while others are anti-inflammatory, meaning they reduce inflammation.

Mutations in the ADA2 gene severely reduce or eliminate the activity of adenosine deaminase 2. Researchers do not fully understand how a shortage (deficiency) of this enzyme's activity leads to vasculitis and immune system abnormalities. They speculate that the enzyme deficiency may disrupt the balance between pro-inflammatory and anti-inflammatory macrophages in various tissues, leading to a buildup of pro-inflammatory macrophages and abnormal inflammation.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

More than 160 individuals with ADA2 deficiency have been described in the medical literature. However, researchers suspect that many more people may be affected, and ADA2 deficiency may not be a rare disease. They are working to determine whether this condition could underlie other, more common forms of vasculitis and stroke whose causes are currently unknown.

Understanding terms used in the source

These definitions explain medical words used above. A definition is not evidence that another condition is present, and it does not predict how a symptom will develop. Ask the clinician which terms apply to the actual examination or test result.

Livedo racemosa

Livedo racemosa describes a reddish-blue mottling of the skin in an irregular, reticular pattern. It differs from the more common livedo reticularis by its shape. Livedo racemosa consists of broken circular segments resulting in a seemingly larger pattern, as opposed to the fine, regular, complete network of livedo reticularis. Livedo racemosa results from permanent impairment of peripheral blood flow and, unlike livedo reticularis, it persists on warming.

Recurrent

Applies to a sign, symptom or manifestation that occurs multiple times separated by intervals in which the sign, symptom, or manifestation is not present.

Affected

This term applies to a family member who is diagnosed with the same condition as the individual who is the primary focus of investigation (the proband).

Which doctor should you see?

The suggested department for discussing Adenosine deaminase 2 deficiency is Rheumatology, with a rheumatologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Are the findings inflammatory, structural or due to another mechanism?
• Is there evidence that other organs need assessment?
• How will function and any treatment-related risks be monitored?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Adenosine deaminase 2 deficiency. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.