Yao syndrome shares some symptoms of Blau syndrome. Both conditions are associated with disease-causing variants in the NOD2 gene. Common symptoms include fever, oral ulcers, skin rash, joint pain, gastrointestinal upset, unintentional weight loss, general malaise, lower limb swelling and fatigue.

The key distinction between Yao and Blau syndromes are in the eye and skin symptoms. Yao syndrome does not generally involve uveitis (inflammation of the uvea in the eye) that is seen in Blau syndrome, and the Yao syndrome rash rarely has the granuloma (lumpy) rash type that is seen in Blau syndrome.

Abdominal symptoms in Yao syndrome have been described as Crohn’s-like, although these appear to be clinically distinct from Crohn’s disease, despite Crohn’s disease also being associated with the NOD2 gene.

Constitutional symptoms such as fever, fatigue and general malaise are more prevalent with Yao syndrome, while these have been reported to develop later in untreated Blau syndrome.

Flares can vary significantly from person to person. Flares can last from a few days to several weeks or even months. The frequency and duration of flares can also vary over time in the same individual.

Disease-causing variants in the NOD2 gene are thought to cause Yao syndrome. This gene sits on chromosome 16, which is an autosome, as opposed to a sex chromosome. And only one copy of the gene with the disease-causing variant is needed to develop Yao syndrome. This is why inheritance is said to be autosomal dominant.

Simply put:

This gene provides instructions for making a protein that helps the body detect bacteria and other pathogens. Disease causing changes in the NOD2 gene can lead to an overactive innate immune response, resulting in chronic inflammation and the symptoms associated with the disease. 

More in depth:

The NOD2 gene provides instructions for the body to make the NOD2 protein. (NOD2 gene italics. NOD2 protein no italics. Rules of science.) The NOD2 protein is involved in innate immunity. It’s a receptor, like a cellular guard, and when it receives a signal that there is some kind of problem, it relays that signal to activate an inflammation pathway. If it sends a relay without a signal, that inflammation pathway gets switched on when it is not needed. This may happen when there is just too much NOD2 being made, which is one possibility under consideration due to the type of the genetic change in NOD2 that seems to produce the symptoms of Yao syndrome that are not seen in Blau syndrome.

Beyond that it’s not really known how NOD2 causes the disease, but granulomas (clusters of immune cells build up) do not appear to be a feature of Yao syndrome as they are in Blau syndrome. Yao syndrome does not involve sarcoidosis that is seen in Blau syndrome.

The symptom differences would suggest a different mechanism, and this is why Yao has been set apart as a separate condition, although it’s also possible that we could be looking at the same disease on a spectrum.

Diagnosis of Yao syndrome typically involves a combination of:

Clinical evaluation: Assessing the patient's symptoms, medical history, and family history.

Physical examination: Looking for signs of arthritis, skin rashes, and other characteristic features.

Laboratory tests: Blood tests to measure inflammatory markers (e.g., ESR, CRP), Full blood count,

Genetic testing: Sequencing the NOD2 gene to identify disease-causing variations.

Yao syndrome can be diagnosed by a genetic test in patients who are displaying the symptoms associated with Yao syndrome.

As most cases of Yao syndrome are diagnosed in adulthood, a rheumatologist will usually take a patient through a process of ruling out infections and other similar conditions before determining that the patient may be a candidate for Yao syndrome and arranging for genetic testing. This process can take a frustratingly long time.

It is important to follow up throughout this diagnostic process, as delays in diagnosis and inappropriate treatment regimens may have significant health consequences.

There is no specific cure for Yao syndrome, and treatment focuses on managing symptoms and reducing inflammation.

Medications commonly used include:

Biologic agents:

TNF inhibitors e.g., etanercept, adalimumab

Tocilizumab has also been reported as effective.

 IL-1 inhibitors e.g., anakinra, canakinumab (these may be difficult to access in Australia and New Zealand)

Disease-modifying antirheumatic drugs (DMARDs): Such as methotrexate or sulfasalazine, to help control the underlying inflammation and have been reported to help joint symptoms.

Nonsteroidal anti-inflammatory drugs (NSAIDs): To relieve pain and inflammation.

Corticosteroids: To reduce inflammation during acute flares.

Colchicine: Can be used to manage some of the inflammatory symptoms.

Given the gastrointestinal involvement in Yao syndrome, and the association between its causative gene NOD2 with Crohn’s disease, biologics that target TNF-α may also be considered for patients who do not respond to the anti-IL-1 drugs.

Yao syndrome is a serious condition that can impact on a person’s quality of life. If Yao syndrome is not diagnosed and treated correctly, insidious symptoms including general malaise and fatigue can rob a person of living their best life. Serious symptom flares can result in frustrating visits to hospital which can involve expensive and inappropriate tests and treatments.

Because symptoms can be non-specific, intermittent and develop slowly over time, sometimes patients are seen as having a non-specific infection or a reaction to something that will pass. Delayed diagnosis and misdiagnosis are common in this rare disease, and casual dismissal can result in patients learning to avoid seeking medical help.

Specialist Follow-up

People living with Yao syndrome should have regular follow-up appointments with a rheumatologist or immunologist. Management often requires a multidisciplinary approach also involving gastroenterologists, and other specialists. These check-ups are important for monitoring disease activity, adjusting treatments as needed, and addressing any concerns that might arise during the course of the condition.

Medication Adherence

Taking prescribed medications exactly as directed is crucial. Sticking to the recommended medication regimen helps manage symptoms, prevent flare-ups, and reduce the risk of complications.

Trigger Avoidance

It is important to identify and avoid triggers that could make symptoms worse. Common triggers can include stress or infections. By being aware of these factors, people can take proactive steps to minimise the impact on their health.

Healthy Lifestyle

Maintaining a balanced diet and engaging in regular exercise support overall wellbeing and may help in managing Yao syndrome. These healthy habits can also improve energy levels and promote better joint function.

Joint Protection

Protecting the joints from excessive strain is recommended. This might involve adapting activities or using supportive devices to reduce pressure on the joints and prevent injury or further discomfort.

Vaccinations

Vaccinations should be kept up to date according to your doctor’s advice. However, it is important to discuss vaccination plans with your specialist first, as live vaccines may not be suitable for people taking immunosuppressant medications.

The Importance of Ongoing Monitoring

Once a diagnosis of Yao syndrome is made, it may be challenging to find the right treatment balance. Long-term monitoring is essential. Regular reviews with specialists will help ensure that treatment remains effective and that any new symptoms or concerns are addressed promptly.

So, is Yao syndrome autoinflammatory or autoimmune?

Because Yao syndrome is caused by a gene (NOD2) that carries instructions for a protein (NOD2) that is part of the innate (non-specific) immune system, and symptoms are caused by generalised inflammation, Yao syndrome is clearly autoinflammatory. Autoimmune diseases involve the adaptive (specific) immune system.