Patient education: Hereditary alpha-tryptasemia (The Basics)

What is hereditary alpha-tryptasemia? — Hereditary alpha-tryptasemia ("HaT") is a genetic trait that 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 what 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 your cells how to make different proteins, and they give instructions about how your 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 that 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 with HaT have no symptoms or known problems because of it. But some do.

When symptoms happen, they most often involve serious allergic reactions. The medical term for a full-body allergic reaction is "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 that 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 that 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 that 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 for HaT. 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 that make you less sensitive to bee venom. This means that you will be less likely to have anaphylaxis.

If you have had anaphylaxis in the past, your doctor will prescribe a medicine called "epinephrine" to carry with you. It comes in pre-filled "injectors," so you can give yourself a shot if needed.

What else do I need to know? — If you have HaT, it is very likely that 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.

At this time, experts do not recommend that relatives of people with HaT get tested to find out if they have it too, unless they have had anaphylaxis themselves. That's because for people with no symptoms, no treatment is needed.

More on this topic

Patient education: Insect allergy (The Basics)
Patient education: Anaphylaxis (The Basics)
Patient education: How to use an epinephrine autoinjector (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)