Final answer:
Common Variable Immunodeficiency (CVID) is typically characterized by recurrent respiratory and gastrointestinal infections due to reduced levels of serum immunoglobulins. It is a form of acquired immunodeficiency that is sometimes caused by a genetic defect but more often develops later in life.
Step-by-step explanation:
Common Variable Immunodeficiency (CVID), often presenting in adolescents or adults, typically manifests with recurrent respiratory and gastrointestinal infections. While rare, it can be caused by a defective gene, similarly to inherited immunodeficiency disorders such as hypogammaglobulinemia. However, CVID is more frequently an acquired condition characterized by reduced levels of serum immunoglobulins due to B-cell dysfunction. Patients with CVID are at an increased risk of infections because their immune systems produce insufficient antibodies to fight off pathogens effectively.
The diagnosis of CVID includes excluding other forms of primary immunodeficiencies, such as X-linked agammaglobulinemia, where there's an absence of serum immunoglobulin, or severe combined immunodeficiency disease (SCID), which severely affects both B-cell and T-cell functions. CVID shares certain clinical features with these conditions, such as increased susceptibility to infections, but differs in genetics and antibody profiles. Moreover, unlike SCID, which is diagnosed early in life due to severe infections, CVID typically becomes symptomatic later, sometimes not until adulthood.