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What is Mast Cell Activation Syndrome?

Mast Cell Activation Syndrome (MCAS) forms part of a spectrum of mast cell disorders caused by the abnormal proliferation, accumulation, function and/or activation of mast cells. It causes a wide range of unpleasant, frequently debilitating allergic and inflammatory symptoms in many different systems of the body.

People with MCAS can react to a wide range of triggers and potentiating factors including foods, chemicals, drugs, fragrances, temperature, exercise, stress, hormonal fluctuations and infection.

The onset of MCAS can be unpredictable, affecting both children and adults, and presents with a wide range of symptoms in multiple body systems, ranging from hives and rashes, respiratory problems, syncope, gastrointestinal pain, diarrhoea, reflux, neurological problems including anxiety and brain fog, bone pain, and anaphylaxis.

The complex, multisystem nature of MCAS can make gaining a diagnosis particularly challenging. The ability to gain a diagnosis is also negatively impacted by a lack of universally accepted diagnostic criteria and access to diagnostic biomarkers.

There is an urgent need to give a voice to patients, support doctors and researchers, and inform policy-makers about this widely under-recognised condition.

With your support, we feel confident that we can make a substantial difference to the lives of those affected by MCAS and their families.

You can read our collection of patient stories here.

Symptoms of MCAS

The symptoms of MCAS are often unpleasant, sometimes debilitating and can include life-threatening anaphylaxis. These symptoms usually involve multiple systems of the body and can include skin (dermatologic) symptoms, gastrointestinal symptoms (such as abdominal pain, nausea and vomiting), respiratory symptoms, neurological problems and urinary issues.

MCAS symptoms are often episodic or wax and wane (meaning that they go and come back) and their severity can fluctuate over time. In some cases, people may suffer mild symptoms for a long time before experiencing a sudden increase in the frequency or severity of symptoms. Possibly after a particularly triggering incident for the immune system, such as a severe infection or a medical procedure or operation.

Read More TextThe extent of symptoms for people suffering MCAS can be substantial. The potential severity of symptoms paired with the unpredictability of triggers can mean that the everyday lives of people with MCAS, their families and carers are considerably impacted.

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Mast Cell Mediators

Mast cells are a type of blood cell which are found in all body tissues. These cells play a key role in the immune system. In the event of an injury or an infection, mast cells become active and release chemicals called mediators. In a healthy state, mast cell mediators create a number of protective responses in the body to help fight infection and promote healing.

The table shows how these mediators can affect the body during this response.

Comorbidities

Observational studies and patient-reported data show ‘clustering’ of MCAS with other conditions, meaning that people who have MCAS often also have at least one additional condition. Common comorbidities include connective tissue disorders, e.g. Ehlers Danlos Syndrome (EDS) and Marfans, dysautonomia, such as postural orthostatic tachycardia syndrome (POTS), and type 2 diabetes. The relationship between MCAS and many of these comorbidities is yet to be fully understood, and more research is required.

Further information on comorbidities can be found in the Royal College of GPs Ehlers Danlos Syndromes Toolkit. 

Useful presentations

Watch two presentations given by Dr Alex Croom and Dr Bethan Myers at the 2019 PoTs Masterclass in the UK for more information on MCAS. 

Watch two presentations given by Dr. Anne Maitland from the ICAHN school of medicine at Mount Sinai in the US:

Listen to Dr. Theoharis Theoharides explain more about mast cells and the role of mast cell activation in the immune system here

Further reading

Akin C. Mast cell activation syndromes. J Allergy Clin Immunol. 2017;140(2):349-355.

Molderings GJ, Haenisch B, Bogdanow M, Fimmers R, Nöthen MM. Familial occurrence of systemic mast cell activation disease. PLoS One. 2013;8(9):e76241. Published 2013 Sep 30.

Theoharides TC, Tsilioni I, Ren H. Recent advances in our understanding of mast cell activation - or should it be mast cell mediator disorders?. Expert Rev Clin Immunol. 2019;15(6):639-656.

Afrin LB, Ackerley MB, Bluestein LS, et al. Diagnosis of mast cell activation syndrome: a global "consensus-2". Diagnosis (Berl). 2020;/j/dx.ahead-of-print/dx-2020-0005/dx-2020-0005.xml.

Simons FER, Ardusso LR, Bilò MB, et al. International consensus on (ICON) anaphylaxis. World Allergy Organization Journal.

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