Primary Immunodeficiency (PI) is a disease that results whenever one or more essential parts of the immune system is missing or not working properly at birth because of a genetic defect. Since the immune system is tremendously complex, hundreds of things can go wrong during development and sometimes the backup systems cannot compensate for the defects.

 

A variety of developmental errors in the immune system create different types of PIs. They make people susceptible to different kinds of germs and create different sets of symptoms.

 

The immune system is a body-wide network of organs, tissues, cells and protein substances that work together to defend the body against attacks by “foreign” invaders.

 

PI diseases were once thought to be rare, mostly because only the more severe forms were recognized. Today physicians realize that PIs are not uncommon. They are sometimes relatively mild, and they can occur in teenagers and adults as often as in infants and children.

 

Very serious inherited immunodeficiencies become apparent almost as soon as a baby is born. Many more are discovered during the baby’s first year of life. Others—usually the milder forms—may not show up until people reach their twenties and thirties. There are even some inherited immune deficiencies that never produce symptoms.

 

The exact number of persons with PI is not known. It is estimated that each year about 400 children are born in the United States with a serious PI. The number of Americans now living with a primary immunodeficiency is estimated to be between 25,000 and 50,000.*

 

Source: National Institute of Allergy and Infectious Diseases (NIAID), National Institute of Health