Genes are the building blocks of human growth and development. They determine many characteristics, like hair and eye color. Genes also affect the way the immune system functions or how it responds to threats. Primary immunodeficiency disorders are present at birth. They are inherited, which means they are related to genes passed from one generation to another. Some immune disorders are diagnosed at or shortly after birth. Other immune disorders may not be diagnosed until later in childhood or early adulthood.

Researchers continue to learn how genes influence immune disorders. For example, one genetic defect may block certain cells defending the body. Another defect might prevent the removal of toxic chemicals from the body.