What is Hereditary Alpha Tryptasemia?

Hereditary alpha tryptasemia (HαT) is a genetic trait that can cause higher-than-normal blood tryptase levels. It is linked to mast cell disorders. Learn about HαT symptoms, testing and treatment options.

At a Glance: Hereditary Alpha Tryptasemia

  • Defining Hereditary alpha tryptasemia (HαT). HαT is a genetic trait that causes high levels of tryptase, a protein made by mast cells, in the blood.
  • Most people with HαT have few or no symptoms. Some may have skin, digestive, heart, bone, or other symptoms, including frequent allergic reactions.
  • HαT may increase the risk of severe allergic reactions and anaphylaxis. People with certain allergies or mast cell disorders are at higher risk.
  • How is HαT diagnosed? HαT is diagnosed using a blood test and a special genetic test. The test is called tryptase genotyping, also known as a Tryptase CNV or HαT test.
  • Can you cure HαT? There is no cure for HαT, but medicines can help manage symptoms. Epinephrine is the first-line treatment for anaphylaxis.

Hereditary alpha tryptasemia (HαT) is a genetic trait. It was first identified in 2014. What causes HαT – elevated basal serum tryptase levels – was determined two years later. HαT occurs in 5.5% of general populations where it has been studied. However, the majority of people with HαT are white.

People with this genetic trait have high alpha tryptase levels. Tryptase is a protein made by mast cells. It is found in high concentrations around blood vessels and mast cells.

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High tryptase levels serve as a marker for mast cell activation. This can play a major role in allergic reactions. During allergic reactions, mediators from mast cells (including tryptase) enter your bloodstream.

People with HαT already have high tryptase levels, even if they aren’t having an allergic reaction. This can lead to a host of severe symptoms. People with HαT are at risk for a severe or life-threatening allergic reaction, or anaphylaxis.

Many people are not aware they have HαT. About one-third of people with HαT show symptoms. The remaining two-thirds show few symptoms or no symptoms at all. Since HαT is a genetic condition, there is at least a 50% chance the trait can be passed on to a child.

HαT is more common in people who have mastocytosis. This is a condition where increased levels of mast cells cause symptoms that mimic severe allergic reactions, often without a known cause. It is believed the presence of HαT may cause mastocytosis symptoms to be more severe. Research is ongoing.

Research so far has found no direct link between HαT and asthma, allergic rhinitis, GERD, atopic dermatitis, or irritable bowel syndrome. It is possible that HαT could worsen allergic diseases if they are untreated.

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Signs and Symptoms of Hereditary Alpha Tryptasemia

HαT-associated symptoms can vary from person to person. People with HαT may show the following symptoms:

  • Skin. Rashes, flushing
  • Digestive. Stomach or abdominal pain, bloating, diarrhea or constipation, reflux, heartburn, difficulty swallowing (some of these symptoms may first be diagnosed as irritable bowel syndrome)
  • Heart. Fast heartbeat, blood pressure changes, fainting
  • Muscle and bones. Joint pain, back pain, being double-jointed, scoliosis
  • Mental health. Brain fog, anxiety, panic attacks
  • Chronic pain
  • Frequent allergic reactions
  • Severe or life-threatening anaphylaxis

HαT may not be the cause of these symptoms. But it is likely the symptoms are worsened by HαT.

People with HαT have elevated tryptase levels. This may put them at risk for severe mast cell-mediated allergic reactions, including anaphylaxis.

Triggers may include an insect sting, certain foods, certain medications, or even skin friction or vibration (such as from a lawnmower). When people with insect venom allergy have elevated tryptase, they tend to have more frequent severe reactions when stung. People with food allergies with elevated tryptase also tend to have more severe reactions.

Anaphylaxis can affect multiple body systems. These may include the skin (itchy hives), digestive tract (swelling of the mouth, tongue or throat, nausea, vomiting, diarrhea), respiratory system (shortness of breath), and heart (increased heart rate).

In some cases, a severe allergic reaction may happen without an apparent cause. This is called idiopathic anaphylaxis. HαT is more common among people with idiopathic anaphylaxis.

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How is Hereditary Alpha Tryptasemia Diagnosed?

Your doctor will evaluate you for clinical features of HαT (including medical history) and take a blood test to measure for elevated serum tryptase levels. This test should be done when you have minimal or no symptoms. The test should not be done until at least 24 hours have passed after symptoms of a recent allergic reaction. The presence of symptoms may affect the test results.

If the blood test shows elevated tryptase levels, your doctor should follow up with a special genetic test. This test checks to see if you inherited extra copies and versions of the alpha tryptase gene. The test is called tryptase genotyping (also called a “Tryptase CNV test” or “HαT test”).

Misdiagnosis and delayed diagnosis are common with HαT. Some people may have both HαT and mastocytosis, which can complicate the diagnosis. Other people may have symptoms not caused by HαT, especially if the symptoms do not respond to medications that treat mast-cell related allergic reactions.

It’s important to advocate for yourself for continued evaluation if problems persist after treatment.

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Treatment for Hereditary Alpha Tryptasemia

HαT is a genetic trait and no medications are currently available that can inhibit or block tryptase itself. Treatments for HαT-related symptoms are available. These treatments may require some trial and error until the best option is identified.

Treatments may include:

  • Allergy medicines (antihistamines)
  • Mast cell stabilizers
  • Corticosteroids
  • Epinephrine (to treat anaphylaxis)

Some doctors may recommend an anti-IgE medication such as the biologic omalizumab (Xolair®). But currently this is not an FDA-approved treatment for HαT. One study of allergic asthma patients found that having more alpha tryptase was linked to a better response rate to omalizumab.

Talk with your doctor about what treatment is best for you.

If you have HαT and you are at risk for anaphylaxis, make sure you know your triggers and how to avoid them. Epinephrine is the first line of treatment for anaphylaxis. If you are prescribed epinephrine to treat anaphylaxis, keep it with you at all times. You will need to carry two devices of epinephrine in case symptoms return after the first dose. If symptoms are severe, they worsen or persist, or they come back, administer the second dose. Then seek emergency medical treatment.

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Is Hereditary Alpha Tryptasemia a Form of Mast Cell Disease?

HαT is often considered a type of mast cell disorder. The two conditions have similar symptoms. They respond to the same types of treatment. However, having HαT may not necessarily mean there’s a mast cell problem. And it may not cause allergic disease or another medical issue. More research is needed to determine how mast cells contribute to HαT.

Questions & Answers (Q&A) on Hereditary Alpha Tryptasemia (HαT)

Here are some common questions about HαT. Please email the editor if you have other questions not listed below.

Most people with high blood tryptase levels have HαT. The only way to know for sure if you have HαT is to have a special genetic test that counts the copies and versions of tryptase you have inherited.

Multiple studies in the United States and European Union have found people with HαT are more likely to have systemic mastocytosis or another clonal mast cell disease. As a result, they are more likely to experience symptoms and be at risk for anaphylaxis.

People with HαT or a mast cell disease should talk with their doctor about both conditions. More people with mast cell diseases have the HαT trait than in the general population. This includes systemic mastocytosis, idiopathic anaphylaxis, and mast cell activation syndrome (MCAS).

Your doctor can determine appropriate HαT testing and, if needed, treatment.

Yes. Based on associated clinical features, HαT is linked with all forms of MCAS. However, HαT is not believed to cause MCAS. Instead, it is believed that what causes mast cells to activate is made worse by HαT.

Make an appointment with a doctor to discuss testing for HαT. You may want to see a specialist for testing. Board-certified allergists are specialists who can test you for HαT.

Idiopathic MCAS occurs when there is no known trigger. When you don’t know what is causing symptoms, MCAS can be frustrating to manage. Medications can help reduce the severity and frequency of symptoms.

Mastocytosis is a mast cell disorder. It involves several types, from mild to severe. Hereditary alpha tryptasemia (HαT) is a genetic trait that can cause frequent and severe mast cell-mediated reactions like anaphylaxis. HαT has been linked to mastocytosis, MCAS with idiopathic anaphylaxis, and severe reactions to stinging insects.

Mast Cell Disease Resources

These resources can help you prepare for appointments, plan for emergencies, and connect with others who understand life with mast cell disease. 

New to mast cell disease? Start here →

A new diagnosis can bring many questions. You do not need to learn everything at once. The Mast Cell Disease Society (TMS) offers information about mast cell diseases, testing, treatment, and life after diagnosis. 

Visit The Mast Cell Disease Society and choose “New Patients – Start Here” to begin. 

Find a doctor familiar with mast cell diseases 

Finding a healthcare professional who understands your condition can help you take the next step in your care. TMS offers a Find an HCP Resource to help you explore care options. 

Before scheduling, ask whether the doctor treats your specific condition, sees patients in your age group, and requires a referral. You can also check whether the office accepts your insurance. 

Track symptoms and prepare for appointments 

A symptom record can help you explain what happens between doctor visits. TMS offers a symptom tracker and patient guides to help you record symptoms, possible triggers, medicines, and reactions. 

Bring your notes, medicine list, and questions to your appointment. You may want to ask: 

  • What do my test results mean? 
  • What should I do when my symptoms get worse? 
  • How will we know whether my treatment is working? 
  • Which symptoms need emergency care? 

Use this MCD Glossary to look up unfamiliar words. Ask your healthcare team to explain how each term relates to your care. 

Prepare for emergency care 

Planning ahead can make it easier to share important information during an emergency. TMS provides an Emergency Alert Card and an Emergency Room Response Plan through its patient resources page. 

Review these materials with your doctor. Ask your doctor to help create a plan specific to your needs, including when to use prescribed emergency medicine and when to seek emergency help. Share your plan with family members and others who may help during a reaction. 

Connect with others who understand MCD 

Living with mast cell disease can feel isolating. Talking with people who have similar experiences may help you feel understood and give you a place to share everyday concerns. 

TMS offers virtual support groups and online communities. Visit TMS’s Find Support page to explore ways to connect. 

Find information for everyday life about Mast Cell Disease 

You may have questions about daily routines, relationships, or the emotional effects of living with a long-term condition. These Allergy & Asthma Network guides offer more information: 

October 2026
Reviewed by:
Jonathan Lyons, MD, is a board-certified allergist and immunologist at the University of California, San Diego. He is chief of the Translational Allergic Immunopathology Unit in Laboratory of Allergic Diseases at the National Institutes of Allergy and Infectious Diseases (NIAID). Dr. Lyons has received NIAID Merit Wards for his groundbreaking work in characterizing pathways leading to increased mast cell hyperactivity and anaphylaxis in people with hereditary alpha tryptasemia.