The high rates of infection in patients with low IgA and IgGScD result in decreased lung function,72 and in particular IgG4ScD correlates with the presentation of bronchiectasis.78 In some cases, low IgA may evolve into the more severe CVID, and a decrease in IgGSc concentrations may occur before a decrease in total IgG.20,78,79 An algorithm for the testing of IgGSc in individuals with low IgA and utility is shown in Figure 2. This evidence concerns the gene CD79A and infection.