What is the most common primary immunodeficiency disorder?

Selective IgA deficiency is recognized as the most common primary immunodeficiency disorder. This condition is characterized by an undetectable level of immunoglobulin A (IgA) in the serum and secretions, primarily affecting mucosal immunity. Individuals with selective IgA deficiency may experience recurrent infections, particularly those involving mucosal surfaces, such as respiratory and gastrointestinal infections. While many individuals with this deficiency can remain asymptomatic, some may develop autoimmune diseases or allergic conditions.

In contrast, other disorders listed, although significant, occur less frequently. Common variable immunodeficiency primarily presents later in life and involves a broader range of immunoglobulin deficiencies. Isolated IgG deficiency, while more common than some forms of immunodeficiency, does not surpass the prevalence of selective IgA deficiency. X-linked agammaglobulinemia, which is predominantly seen in males, is a much rarer condition resulting from a failure of B-cell development, leading to significantly reduced immunoglobulin levels.

Therefore, in terms of overall prevalence in the general population, selective IgA deficiency stands out as the most frequent primary immunodeficiency.