In the first study that included patients over 18 years of age, by Szymanska et al. [68], increased serum zonulin concentrations were found in various immunopathological diseases, such as food allergies, gastrointestinal tract infections, systemic autoimmune diseases, and inflammatory bowel diseases, although there are discrepancies in the concentration of zonulin in plasma and the concentration of fecal zonulin [69]. This evidence concerns the gene HP and inflammatory bowel disease.