A 28-year-old man presents with recurrent sinopulmonary infections. Blood tests reveal a significant deficiency in IgA levels, with normal levels of other immunoglobulins. What is the most likely diagnosis?

• A. Selective IgA deficiency
• B. Wiskott-Aldrich syndrome
• C. IgG subclass deficiency
• D. X-linked agammaglobulinemia

Answer: (A)