Common variable immunodeficiency disease or CVID is a group of about 150 immunodeficiency disorders that are all characterized by low levels of all three types of immunoglobulin in the blood and the lack of any other underlying condition.
The disease can be caused by a number of different causes, many of which are genetic in origin. A patient will not properly produce antibodies in response to infection (even dead or damaged diseases used in a vaccination). They therefore become home to many opportunistic and uncommon infections.
CVID is a classic zebra diagnosis, even though it is fairly common in the population. Its symptoms mimic other immunodeficiency diseases and infections, such as AIDS and Whipple's disease. Although patients will consistently show low immunoglobulin levels, this alone is not enough to establish a diagnosis. As such, CVID is a diagnosis of exclusion. Many cases will take even a skilled immunologist years to reach a definitive diagnosis.
Undiagnosed patients are usually not killed by the disease, but by opportunistic infections. However, diagnosed patients usually respond well to immunoglobulin injections and can lead fairly normal lives.