PLCG2-associated antibody deficiency and immune dysregulation

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

PLCG2-associated antibody deficiency and immune dysregulation (PLAID) is an immune system disorder characterized by an allergic reaction to cold temperatures. Other immune system problems can also occur. The hallmark feature of PLAID is the development of a red, itchy rash (hives) when the skin is exposed to cool temperatures, which is known as cold urticaria. In PLAID, the hives typically develop in response to evaporative cooling, such as when a cool breeze or air conditioning blows on damp or sweaty skin. Being in a cold swimming pool can also trigger hives. In contrast, people with PLAID do not have a reaction when they touch a cold object, like an ice cube. (The ice cube test is a common test for a cold allergy; it triggers a reaction in people with other forms of cold urticaria, which usually begin later in life than PLAID.) However, some people with PLAID do experience a burning sensation in their throats when they eat cold foods, like ice cream. In PLAID, the hives go away once the skin warms up. Prolonged exposure to cold can lead to loss of consciousness or a serious allergic reaction known as anaphylaxis.

Other skin problems can also occur in PLAID. A small number of affected individuals develop a blistering rash on the tip of their nose, ears, and fingers shortly after birth. The rash usually heals on its own in infancy, although in rare cases, it worsens over time. After the initial rash goes away, a different rash sometimes develops on the torso and limbs later in life. This rash, called a granuloma, can affect small patches of skin or be widespread. In people with PLAID, the granulomas do not occur in warm regions of the body, such as the armpits and other skin folds.

In many people with PLAID, immune system function is reduced, leading to recurrent infections such as frequent colds, ear infections, or bouts of pneumonia. The infections are likely related to lower-than-normal levels of special proteins called antibodies or immunoglobulins, particularly immunoglobulin M (IgM) or immunoglobulin G (IgG). Antibodies attach to specific foreign particles and germs, marking them for destruction. The number of immune system cells called natural killer (NK) cells may also be reduced.

Autoimmune disorders, which occur when the immune system malfunctions and attacks the body's own tissues and organs, can also occur. Autoimmune disorders associated with PLAID include autoimmune thyroiditis and vitiligo. Autoimmune thyroiditis results from damage to the butterfly-shaped, hormone-producing gland in the lower neck (the thyroid). Vitiligo is caused by attacks on the pigment cells in the skin, resulting in a patchy loss of skin coloration. Most people with PLAID have abnormal antibodies called autoantibodies in their blood. One such antibody common in people with PLAID is known as antinuclear antibody (ANA). Autoantibodies attach to normal proteins and can trigger an immune attack against the body's own tissues. However, not everyone with these abnormal antibodies has an autoimmune disease.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

PLAID is caused by mutations in the PLCG2 gene, which provides instructions for making an enzyme called phospholipase C gamma 2 (PLCγ2). This enzyme is found predominantly in immune system cells and is critical for the cells' roles in preventing infection by recognizing and attacking foreign invaders, such as bacteria and viruses.

The PLCG2 gene mutations that cause PLAID remove (delete) segments of DNA from the gene. These changes alter a region of the PLCγ2 enzyme that controls whether it is turned on or off. The altered enzyme does not function properly. At lower temperatures, the enzyme is constantly active, rather than being turned on only when needed. It is thought that when the skin is cooled, the PLCγ2 enzyme is turned on, and the abnormal activity triggers an immune reaction, resulting in hives and skin rashes. Researchers are unsure if a similar mechanism underlies autoimmune disease in people with PLAID. Researchers speculate that the abnormal activity of the enzyme occurs in only a small range of cool temperatures. Direct contact with a cold object, such as an ice cube, may be too cold to turn on the enzyme, which might explain why people with PLAID do not react to the ice cube test.

In contrast, at normal body temperature, the PLCγ2 enzyme's activity is reduced. The resulting impairment of immune cell function prevents the body from effectively fighting foreign invaders, leading to recurrent infections.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

In most cases, an affected person has one parent with the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

PLAID is a rare disorder whose prevalence is unknown. Only a few affected families have been reported in the medical literature.

Which doctor should you see?

The suggested department for discussing PLCG2-associated antibody deficiency and immune dysregulation 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 PLCG2-associated antibody deficiency and immune dysregulation. 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.