People with this deficiency lack immunoglobulin A (IgA), a type of antibody that protects against infections of the mucous membranes lining the mouth, airways, and digestive tract.

85–90% of IgA-deficient individuals are asymptomatic, although the reason for lack of symptoms is relatively unknown and continues to be a topic of interest and controversy.

Patients have an increased susceptibility to pneumonia and recurrent episodes of other respiratory infections and a higher risk of developing autoimmune diseases in middle age.

[3] IgA deficiency and common variable immunodeficiency (CVID) feature similar B cell differentiation arrests,[4] but it does not present the same lymphocyte subpopulation abnormalities.

Selective IgA deficiency is often inherited, but fewer than half of all cases but has been associated with some congenital intrauterine infections.

[citation needed] Types include: When suspected, the diagnosis can be confirmed by laboratory measurement of IgA level in the blood.

[18] As opposed to the related condition CVID, selective IgA deficiency is not associated with an increased risk of cancer.

[19] Patients with Selective IgA deficiency rarely have severe reactions to blood transfusions.