« Understanding Primary Immunodeficiency (PI)

Types of PI

Primary immunodeficiency (PI) diseases are characterized in many different ways, including:

  • Low antibody levels
  • Defects in antibodies
  • Defects in the cells and proteins of the immune system (for example, T cells, B cells, neutrophils, or the complement system)

These defects make people susceptible to recurrent infections, and other complications that may require different therapies. The most common primary immunodeficiency types result in an inability to make a very important type of protein called antibodies or immunoglobulins, which help the body fight off infections from bacteria or viruses. In addition to increased susceptibility to infection, people with PI may also have autoimmune diseases in which the immune system attacks their own cells or tissues.

PI Type:

Ataxia Telangiectasia (A-T)


Definition of Ataxia Telangiectasia

Ataxia telangiectasia (A-T) is a PI disease that affects a number of organs. Among the symptoms is a weakened immune system that involves both T and B lymphocytes, and problems making antibodies (immunoglobulin) resulting in increased susceptibility to infection.

It is characterized by neurologic abnormalities that result in an unsteady walk (ataxia), dilated blood vessels (telangiectasia) in the eyes and skin, immune defects involving T and B lymphocytes, and a predisposition to cancer.

A-T can be inherited, and the gene responsible has been identified.

Symptoms of Ataxia Telangiectasia

The first symptom is generally ataxia, a medical term used to describe an unsteady gait, which appears when a child begins to walk. Other symptoms related to brain abnormalities include issues with eye movements, such as rapidly alternating twitches of the eye and difficulty in controlling eye movements; and difficulty using the muscles needed for speech and swallowing.

Dilated blood vessels cause the whites of the eyes to appear bloodshot, and may also be seen less commonly on the ears, neck, and extremities.

An increased risk of infections caused by bacteria and viruses is also seen in people with A-T, most commonly affecting the lungs and sinuses. Some of this increased risk of infection is related to difficulty swallowing (dysphagia), which can cause aspiration, which occurs when food and liquid go down the windpipe into the lungs rather than the stomach.

Telangiectasia diagnosis Telangiectasia diagnosis

Diagnosis of Ataxia Telangiectasia

Diagnosis of A-T is generally made based on the common clinical features (ataxia, telangiectasia, abnormal eye movement and speech). Lab tests can aid in reaching the diagnosis, especially in early childhood, when the telangiectasia has not appeared.

Lab tests include:

  • Measurement of alpha-fetoprotein, as elevated levels are found in the vast majority of A-T patients after age 18-24 months
  • Absence of the protein made by the A-T gene can also confirm diagnosis
  • Measurement of damage to blood cells after exposure to x-ray
  • Examination of the A-T gene to look for mutations (mistakes)


Treating Ataxia Telangiectasia

Only your doctor can determine which treatment is right for you and your specific health needs. Visit our Treating PI section to read about the types of PI treatment and download questions to ask your doctor.



For more information, please refer to the IDF Patient & Family Handbook for Primary Immunodeficiency Diseases (5th ed) by Blaese RM, Bonilla FA, Stiehm ER, Younger ME, eds.