A 27-year-old man with recurrent sinopulmonary and cutaneous infections.

The increasing availability of genetic testing for modern immunologists in the evaluation of immune diseases could provide a definite diagnosis in elusive cases. A 27-year-old white male patient presented to the clinic with recurrent sinopulmonary and cutaneous infections since childhood. The patient's mother had seronegative polyarthritis, and one of two sisters of the patient had chronic sinopulmonary infections. Serum immunoglobulins, immunoglobulin G (IgG) subclasses, lymphocyte subset markers, mannose-binding lectin, mitogen and antigen stimulation, bacteriophage study, and Streptococcus pneumoniae titers to 23 serotypes were all normal. B-cell phenotyping revealed a decrease in both nonswitched memory B cells (CD19 ⁺ CD27 ⁺ IgD ⁺ ) and switched memory B-cells (CD19 ⁺ CD27 ⁺ IgD ^- ). Genetic testing and the improvement of clinical symptoms after IgG replacement led to the final diagnosis.