Primary immune deficiency (PID) diseases are rare, genetic disorders that impair the immune system. Without a healthy immune response, people are subject to chronic, debilitating infections, such as Epstein-Barr virus, which can increase the risk of developing cancer.
There are more than 200 different forms of PID, some of which can be fatal. PIDDs may be diagnosed in infancy, childhood, or adulthood, depending on severity. The incidence of severe PID needing immediate treatment has been estimated to be 5–10 per 100,000 newborns.