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Disease Profile

Monoclonal mast cell activation syndrome

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Monoclonal MCAD; MMAS


Monoclonal mast cell activation syndrome (MMAS) is a rare immunological disorder characterized by recurrent episodes of allergy, flushing, stomach and intestinal cramping, diarrhea, wheezing, fatigue and a temporary loss of consciousness caused by a fall in blood pressure (hypotension). MMAS is very similar to systemic mastocytosis but without the itchy skin patches known as urticaria pigmentosa. Symptoms may be triggered by a number of factors, including eating, exertion, environmental conditions, emotional stress, or insect stings.[1][2] It is caused by a very small change (mutation) in the KIT gene which results in a defect of the mast cells. Treatment may include antihistamines and other medications, as needed.[2]


Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

    Learn more

    These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

    Where to Start

      In-Depth Information

      • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.

        Selected Full-Text Journal Articles


          1. Akin C. Mast cell disorders. UpToDate. Updated: Apr. 03, 2020; https://www.uptodate.com/contents/mast-cell-disorders-an-overview.
          2. Akin C. Mast Cell Activation Syndrome: Proposed Diagnostic Criteria. J Allergy Clin Immunol. December, 2010; 126(6):1099–104. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3753019/.