CVID is an immune system disorder in which a person has low levels of several of the proteins (antibodies) that help fight infections. CVID leaves an afflicted person open to recurrent infections in your ears, sinuses and respiratory system, and increases risk of digestive disorders, blood disorders and cancer.
CVID is believed to result from mutations in genes that are involved in the development and function of immune system cells called B cells. B cells are specialized white blood cells that help protect the body against infection. When B cells mature, they produce special proteins called antibodies (also known as immunoglobulins). These proteins attach to foreign particles, marking them for destruction. Mutations in the genes associated with CVID result in dysfunctional B cells that cannot make sufficient amounts of antibodies.
Common Variable Immunodeficiency, Mayo Clinic (Feb. 6, 2018), https://www.mayoclinic.org/diseases-conditions/common-variable-immunodeficiency/symptoms-causes/syc-20355821;
Common Variable Immune Deficiency, Genetics Home Reference, http://ghr.nlm.nih.gov/condition/commonvariableimmunedeficiency