Final answer:
Primary immunodeficiency is caused by genetic abnormalities and is characterized by the absence or dysfunction of components of the immune system. Examples include chronic granulomatous disease, X-linked agammaglobulinemia, selective IgA deficiency, and severe combined immunodeficiency disease.
Step-by-step explanation:
The memory cue for primary immunodeficiency is the fact that it is caused by genetic abnormalities. Primary immunodeficiencies are inherited disorders in which elements of the immune system are either absent or functionally defective. They are typically first seen in the clinic as recurrent or overwhelming infections in infants. Examples of primary immunodeficiencies include chronic granulomatous disease, X-linked agammaglobulinemia, selective IgA deficiency, and severe combined immunodeficiency disease.