Version July 2025
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What is hereditary alpha-tryptasemia? —
Hereditary alpha-tryptasemia ("HaT") is a genetic trait some people have. It is not a disease. People with HaT have extra copies of the "alpha-tryptase" gene. The extra copies are inherited from 1 or both parents.
Your genes decide which traits, or characteristics, you have. Genes are made of DNA, which is inside every cell in the body. The genes are like the body's recipe book. They tell the cells how to make different proteins, and they give instructions about how the body should work.
Alpha-tryptase is a type of protein. The alpha-tryptase gene tells specific cells in the body how to make this protein. When a person has HaT, their body makes more alpha-tryptase protein than normal.
HaT is still being studied by experts. They believe about 5 percent of White people in the US and Europe have HaT. Experts do not yet know how common HaT is in other people around the world.
What are the symptoms of HaT? —
Most people have no symptoms or known problems because of it.
When symptoms happen, they most often involve serious allergic reactions. A full-body allergic reaction is called "anaphylaxis." Signs include hives, swelling, and trouble breathing. Anaphylaxis can happen quickly and can cause death if not treated right away.
People with HaT are more likely to have anaphylaxis if they also have 1 of the following problems:
●Systemic mastocytosis – This is a rare disorder in which too many "mast cells" build up in a person's body. Mast cells are a type of white blood cell.
●Bee sting allergy – Some people have a serious allergic reaction if they are stung by a bee, wasp, hornet, or other related insect.
●Idiopathic anaphylaxis – This is a condition in which a person has episodes of anaphylaxis with no known cause.
This is most likely because the extra alpha-tryptase in the body makes these problems worse.
Is there a test for HaT? —
Yes. Most people with HaT find out they have it when they have blood tests after an allergic reaction. Tests might include:
●Tryptase level – After an episode of anaphylaxis, doctors will usually measure the amount of tryptase in a person's blood. Having a higher-than-normal level of tryptase is the first clue a person might have HaT.
●Tryptase genotyping – This test can show how many copies of the alpha-tryptase gene a person has. If you have extra copies, this means you have HaT. This test would only be done if the tryptase level test result was high.
Genotyping is not yet available in most labs or hospitals. It is mostly done as part of research studies.
How is HaT treated? —
There is no specific treatment. This is because it is not a disease, and most people with HaT do not have symptoms or problems because of it.
If you have HaT plus another disorder like systemic mastocytosis or bee sting allergy, you need to get treatment for that problem. This is because HaT can make your other disorder worse. For example, if you have a bee sting allergy, you can get allergy shots to make you less sensitive to bee venom. This means you will be less likely to get anaphylaxis.
People who had anaphylaxis usually get a prescription for epinephrine. It comes in 2 forms:
●A device called an "autoinjector" (sample brand names: Auvi-Q, EpiPen), which has a shot you can give yourself (figure 1)
●A spray that goes in the nose (brand name: neffy) (figure 2)
If your doctor prescribes epinephrine, carry it with you at all times.
Use epinephrine right away if you think you are having a severe allergic reaction. Then, call for an ambulance (in the US and Canada, call 9-1-1). That's because the medicine does not last very long in the body. Symptoms can sometimes come back as the medicine wears off. In the hospital, doctors can watch you and give you more medicine if needed.
What else should I know? —
If you have HaT, it is very likely at least 1 of your parents have or had it, too. You only need to inherit the extra copies of the gene from 1 parent to have HaT. This type of genetic trait is called "autosomal dominant." If you have children, there is a 50 percent chance of each child inheriting HaT from you.
Experts do not recommend relatives of people with HaT get tested to find out if they have it too, unless they had anaphylaxis themselves. That's because for people with no symptoms, no treatment is needed.
Patient education: Allergy to insect stings (The Basics)
Patient education: Anaphylaxis (The Basics)
Patient education: How to give epinephrine (The Basics)
Patient education: Bee and insect stings (Beyond the Basics)
Patient education: Anaphylaxis symptoms and diagnosis (Beyond the Basics)
Patient education: Anaphylaxis treatment and prevention of recurrences (Beyond the Basics)
Patient education: Using an epinephrine autoinjector (Beyond the Basics)
