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BACKGROUND Autoimmune atrophic gastritis (AAG) is a type of chronic gastritis that mainly affects the gastric corpus. Due to the lack of standard diagnostic criteria and overlaps with the courses of Helicobacter pylori -related atrophic gastritis, reports on the diagnostic strategy of AAG at an early stage are limited. CASE SUMMARY A 71-year-old woman with severe anemia was diagnosed with AAG. Endoscopic views and pathological findings showed the coexistence of normal mucosa in the gastric antrum and atrophic mucosa in the gastric fundus. Serological tests showed that anti-parietal cell antibodies and anti-intrinsic factor antibodies were both positive. Immunohistochemical results, which showed negative H + -K + ATPase antibody staining and positive chromogranin A (CgA) staining, confirmed the mechanism of this disease. After vitamin B12 and folic acid supplementation, the patient recovered well. CONCLUSION Successful diagnosis of AAG includes serological tests, endoscopic characteristics, and immunohistochemistry for H + -K + ATPase and CgA antibodies.

Background: Fat intake is one of the most important triggers for symptom development in patients with irritable bowel syndrome (IBS). But long-term restriction in fatty foods ingestion may lead to nutritional inadequacies. In this study, we aim to identify the vital genes that function in lipid-induced gastrointestinal symptoms, contributing to precise management of fat control for IBS patients. Methods: The clinical characteristics of the subjects were collected by questionnaire investigation and analyzed using multivariate logistic regression. Differentially expressed genes (DEG) and signaling pathways were analyzed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. The infiltrated immune cells in the small intestinal mucosa were analyzed using ImmuInfiltration and CIBERSORT packages. Random forest and SVM-RFE algorithms were used to select hub genes. A receiver operating characteristic curve (ROC) was performed to evaluate the diagnostic significance of each hub gene. Gene Set Enrichment Analysis (GSEA) was conducted to clarify the possible molecular mechanisms of hub genes in the pathogenesis of IBS after lipid infusion. Results: Fat intake was positively associated with the risk, severity, and quality of life (QOL) of IBS patients. A total of 116 robust DEGs were identified in patients with IBS after lipid infusion using the GSE166869 dataset and were mainly clustered in the immune and inflammatory pathways. The infiltration levels of Neutrophils, CD4+T cells and M1 Macrophages were significantly higher in IBS patients compared to the healthy controls. Furthermore, infiltration levels of Neutrophils and resting memory CD4+ T cells were inversely related to the expression of hub genes (IGKV1D-43, IGKV1-12, APOD, FCGR2A and IGKV2-29). GSEA results of each hub gene suggested the importance of pro-inflammatory pathways in IBS pathogenesis after lipid infusion. After verification, only APOD and FCGR2A were stably down-regulated in both small intestinal mucosa and plasma of IBS patients. The area under the curve of APOD combined with FCGR2A expression was 0.9. Conclusions: APOD and FCGR2A may act as promising biomarkers for discriminating lipid-sensitive IBS patients and IBS diagnosis. Their potential roles in the immune microenvironment of the small intestinal mucosa may provide a vital clue to IBS precision therapy.