Purpose: Previous studies have shown that diamine oxidase (DAO) is reduced in the colon of patients with gastrointestinal-mediated allergy (GMA).Therefore, we assessed the levels and physiological distribution of DAO across the normal human upper gastrointestinal tract and examined whether DAO is reduced at the upper gastrointestinal tract of patients with GMA.We also evaluated if DAO immunohistochemistry can contribute to the diagnosis of this disease.Methods: We performed a retrospective immunohistochemical analysis on tissue samples endoscopically taken from the upper gastrointestinal tract of 21 patients with GMA and 17 food-tolerant controls.The DAO-staining intensity was analyzed semi-quantitatively: 0 = none, 1 = low intensity, 2 = medium intensity, and 3 = high intensity.Results: Overall, DAO-staining intensity was low across the upper gastrointestinal tract both in controls (median, 1.1; 25th-75th percentile, 0.9-1.3)and in the GMA-group (1.0; 0.8-1.2).The highest DAO signal was observed at the subepithelial lamina propria of all segments.Furthermore, only the DAO-staining intensity in the duodenum was significantly lower in the GMA-group than in the controls (0.8 vs. 1.1;P = 0.04).Additionally, receiver operating characteristic analysis showed moderate accuracy for this method to diagnose GMA.Conclusions: This first immunohistochemical study found DAO present at low levels and similarly distributed across the human upper gastrointestinal tract.Reduced DAO-staining intensity in GMA-patients was found only in the duodenum.This indicates that the small intestine can be most vulnerable to develop histamine-induced symptoms, and that DAOdiagnostics at the upper gastrointestinal tract should be performed only in the duodenum, when GMA is suspected.
Vasilakis et al. (Thu,) studied this question.