Snapshot An 8-month-old girl is brought to the pediatrician due to several episodes of ear infections and recently developed a cough over the past few months. She has been on several courses of antibiotics. The parents deny a family history of recurrent infections. Laboratory testing is remarkable for low IgG levels, with normal IgA, IgM, and IgE levels. Introduction Transient hypogammaglobulinemia ofinfancy (THI) is the delayed onset of normal immunoglobulins level, usually IgG Pathophysiology normal physiology maternal IgG is slowly catabolized after birth IgG is slowly synthesized in infant IgG reaches physiologic level at 3 - 6 months etiology of THI largely unknown Epidemiology transient hypogammaglobulinemia presents at 5-6 months of age Associated conditions may have increased risk for atopy allergic rhinitis atopic dermatitis food allergies Presentation Symptoms often asymptomatic frequent pyogenic infections frequent sinopulmonary infections otitis media sinusitis upper respiratory infections Physical exam typically no findings Evaluation ↓ IgG May also see ↓ IgA and IgM Differential Diagnosis Bruton's agammaglobulinemia IgA deficiency Common variable immunodeficiency Other primary immunodeficiencies Treatment Antibiotics as needed in symptomatic patients If severe, IVIG can also be considered in those with poor antibody response to vaccines Prevention, Prognosis, and Complications Prognosis very good typically resolves by 2-6 years Complications Severe pyogenic infections