The complex workings of the immune system requires the cooperation of various organs, tissues, cells and proteins and thus, it can be compromised in a number of different ways. People who have normal immune function at birth who later acquire some form of immunodeficiency are said to have secondary or acquired immunodeficiency diseases. Examples would include AIDS, age-related immune depression, and other immune deficiencies caused by infections, drug reactions, radiation sickness, or cancer. Individuals who are born with an intrinsically reduced capacity for immunologic activity usually have some genetic alteration present at birth. There are varieties of different genes involved, and they render people susceptible to infection by an assortment of different germs. Some of these diseases are relatively mild with onset in adolescence or adulthood. Others are severely debilitating and severely compromise daily activity. Clinically significant primary immunodeficiencies are relatively rare...