« 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:

Selective IgA Deficiency

Definition of Selective IgA Deficiency

Selective IgA deficiency is one of the most common types of PI. These individuals lack IgA, but usually have normal amounts of other immunoglobulins (antibodies). Many people go undiagnosed because they are never sick enough to be seen by a doctor, while others may develop a variety of severe problems.

Selective IgA Deficiency Selective IgA Deficiency

IgA protects the body at surfaces that come in contact with the environment. These sites are the mucosal surfaces—mouth, ears, sinuses, nose, throat, airways within the lungs, gastrointestinal tract, eyes, and genitals.

IgA antibodies are transported in secretions to these mucosal surfaces and play a role in protecting them from infection, which is why IgA is known as a secretory antibody. Because the area of a person's mucosal surfaces is equal to 1.5 tennis courts, the importance of IgA in protecting these surfaces cannot be overstated.

Although people with selective IgA deficiency do not produce IgA, they do produce all the other immunoglobulins. In addition, the other aspects of their immune systems function properly.

The causes of selective IgA deficiency remain unknown. It is likely there are a variety of causes that vary from person to person.

Low serum IgA, like absent serum IgA, is relatively common. Most people with low serum IgA have no apparent illness; others have symptoms similar to Common Variable Immune Deficiency.

Symptoms of Selective IgA Deficiency

People with selective IgA deficiency are at risk of infections. About half of the patients with selective IgA deficiency who come to medical attention have repeated infections of the ears, sinuses, and bronchi (airways of the lungs), and pneumonia. Some other patients with selective IgA deficiency have gastrointestinal infections and ongoing diarrhea. These common infections affect areas with mucosal surfaces that IgA would protect, and may become chronic.

A second major problem in selective IgA deficiency is the occurrence of autoimmune diseases. These are found in about 25% to 33% of patients with selective IgA deficiency who visit their doctor. In autoimmune diseases, people produce antibodies that attack their own tissues, resulting in inflammation and damage.

Allergies may be more common among people with selective IgA deficiency than in the general population, occurring in about 10% to 15% of these individuals. The types of allergies vary. Asthma is one of the most common allergic diseases that occurs with selective IgA deficiency. Food allergy may also be associated with IgA deficiency.

People with selective IgA deficiency are often considered to be at an increased risk of life-threatening or anaphylactic reactions when they receive blood products, including IVIG, that contain some IgA. This is thought to be due to anti-IgA antibodies that may be found in some IgA-deficient patients.

Selective IgA deficiency diagnosis Selective IgA deficiency diagnosis

Diagnosis of Selective IgA Deficiency

Ongoing or recurrent infections, allergies, autoimmune diseases, and chronic diarrhea—or a combination of these issues—can lead doctors to suspect selective IgA deficiency. The diagnosis is made when the patient's blood tests show an absence of IgA with normal levels of the other major types of immunoglobulins (IgG and IgM).

Treating Selective IgA Deficiency

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.