Blau syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Blau syndrome is an inflammatory disorder that primarily affects the skin, joints, and eyes. Signs and symptoms begin in childhood, usually before age 4.

A form of skin inflammation called granulomatous dermatitis is typically the earliest sign of Blau syndrome. This skin condition causes a persistent rash that can be scaly or involve hard lumps (nodules) that can be felt under the skin. The rash is usually found on the torso, arms, and legs.

Arthritis is another common feature of Blau syndrome. In affected individuals, arthritis is characterized by inflammation of the lining of the joints (the synovium). This inflammation, known as synovitis, is associated with swelling and joint pain. Synovitis usually begins in the joints of the hands, feet, wrists, and ankles. As the condition worsens, it can involve additional joints and restrict movement by decreasing the range of motion in many joints. In people with Blau syndrome, the tendons as well as the joints can be inflamed, causing tenosynovitis.

Most people with Blau syndrome also develop uveitis, which is swelling and inflammation of the middle layer of the eye (the uvea). The uvea includes the colored portion of the eye (the iris) and related tissues that underlie the white part of the eye (the sclera). Uveitis can cause eye irritation and pain, increased sensitivity to bright light (photophobia), and blurred vision. Other structures in the eye can also become inflamed, including the outermost protective layer of the eye (the conjunctiva), the tear glands, the specialized light-sensitive tissue that lines the back of the eye (the retina), and the nerve that carries information from the eye to the brain (the optic nerve). While individuals with Blau syndrome may have normal vision, inflammation of any of these structures can lead to severe vision impairment or blindness.

Some individuals with Blau syndrome develop kidney disease (nephritis) due to inflammation. They may also have deposits of calcium in the kidneys (nephrocalcinosis) and often develop chronic kidney failure. Inflammation of blood vessels (vasculitis) can cause scarring and tissue death in the vessels and impedes blood flow to tissues and organs.

Less commonly, Blau syndrome can affect other parts of the body, including the liver, spleen, lymph nodes, brain, blood vessels, lungs, and heart. Inflammation involving these organs and tissues can impair their function and cause life-threatening complications. Rarely, affected individuals have disturbances in nerve function (neuropathy), episodes of fever, or high blood pressure in the blood vessels that carry blood from the heart to the lungs (pulmonary hypertension).

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Blau syndrome results from mutations in the NOD2 gene. The protein produced from this gene helps defend the body from foreign invaders, such as viruses and bacteria, by playing several essential roles in the immune response, including inflammatory reactions. An inflammatory reaction occurs when the immune system sends signaling molecules and white blood cells to a site of injury or disease to fight microbial invaders and facilitate tissue repair.

The NOD2 gene mutations that cause Blau syndrome result in a NOD2 protein that is overactive, which can alter immune responses and trigger an abnormal inflammatory reaction. However, it is unclear how overactivation of the NOD2 protein causes the specific pattern of inflammation affecting the joints, eyes, and skin that is characteristic of Blau syndrome.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Blau syndrome is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Most affected individuals have one parent with the condition.

In some cases, people with the characteristic features of Blau syndrome do not have a family history of the condition. Some researchers believe that these individuals have a non-inherited version of the disorder called early-onset sarcoidosis.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Blau syndrome is a very rare disorder. It is estimated to affect fewer than 1 in 1 million children worldwide.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal inflammatory response · Very frequent (99-80%)

Any anomaly of the inflammatory response, a response to injury or infection characterized by local vasodilation, extravasation of plasma into intercellular spaces and accumulation of white blood cells and macrophages.

Arthralgia · Very frequent (99-80%)

Joint pain.

Erythema · Very frequent (99-80%)

Redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin.

Hyperpigmentation of the skin · Very frequent (99-80%)

A darkening of the skin related to an increase in melanin production and deposition.

Iridocyclitis · Very frequent (99-80%)

A type of anterior uveitis, in which there is Inflammation of the iris and the ciliary body.

Keratitis · Very frequent (99-80%)

Inflammation of the cornea.

Limitation of joint mobility · Very frequent (99-80%)

A reduction in the freedom of movement of one or more joints.

Papule · Very frequent (99-80%)

A circumscribed, solid elevation of skin with no visible fluid, varying in size from a pinhead to less than 10mm in diameter at the widest point.

Other findings in the same source

From: Orphanet

Additional reported features include Posterior uveitis (Very frequent (99-80%)); Skin rash (Very frequent (99-80%)); Joint swelling (Very frequent (99-80%)); Polyarticular arthritis (Very frequent (99-80%)); Synovitis (Very frequent (99-80%)); Arthritis (Frequent (79-30%)); Camptodactyly of finger (Frequent (79-30%)); Cataract (Frequent (79-30%)); Dry skin (Frequent (79-30%)); Erythema nodosum (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Blau syndrome 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 Blau syndrome. 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.