What is a distinguishing feature of transient hypogammaglobulinemia of infancy?

Transient hypogammaglobulinemia of infancy is characterized by a temporary deficiency in immunoglobulin G (IgG) that occurs during early childhood, typically presenting around 2 to 6 months of age. A key distinguishing feature of this condition is the normalization of IgG levels by 9 to 12 months of age.

In healthy infants, maternal IgG is passed through the placenta and begins to wane after birth, usually resulting in a dip in the infant's own IgG levels before they begin producing their own antibodies. In cases of transient hypogammaglobulinemia, the infant may exhibit low levels of IgG for several months, but these levels are expected to return to normal as the infant matures and their immune system develops, most often by 9 months.

This natural resolution is what differentiates transient hypogammaglobulinemia from other immunodeficiency disorders where low IgG levels would persist much longer or involve additional immunologic abnormalities.

Other options, such as annualized IgM deficiency or persistent low IgG beyond 11 months, do not align with the typical progression of transient hypogammaglobulinemia, as they suggest a more chronic condition. Additionally