As expected, when compared to patients without allergy, SIgAD patients with allergy had higher IgE serum levels (33 UI/mL (IQR 14–55) vs. 474 UI/mL (IQR 49–1119), p = 0.018), whereas they did not have lower IgG, IgA, IgM, or IgG subclass serum levels either at diagnosis or during FU. This evidence concerns the gene IGHE and selective IgA deficiency disease.