All these considerations finally lead to the suggested diagnostic approach of (1) endoscopy with duodenal biopsies, (2) serological testing for tTG-IgA antibodies, (3) quantitative analysis of immunoglobulins and Ig subtypes to rule out IgA deficiency, and (4) testing for parasites and ova in stool, or duodenal aspirate analysis for exclusion of giardiasis. This evidence concerns the gene CD79A and selective IgA deficiency disease.