Low levels of IgG are associated with which immunological disorder?

Low levels of IgG can be primarily associated with Common Variable Immunodeficiency (CVID). This immunological disorder is characterized by a significant decrease in the production of antibodies, which includes reduced levels of IgG, among other immunoglobulins. CVID leads to increased susceptibility to infections, particularly respiratory and gastrointestinal infections, due to the impaired humoral immune response.

While other conditions, such as selective IgA deficiency and IgG subclass deficiency, involve issues with specific immunoglobulin classes, they do not primarily relate to a generalized reduction in IgG levels across the board. High Immunoglobulin M (HIGM) syndrome typically presents with normal or elevated levels of IgM, but low levels of IgG are also common, thus differentiating it from the characteristic presentation of CVID. Therefore, CVID is the more salient condition associated with low levels of IgG.