TJP1 and irritable bowel syndrome: Although most patients with D-IBS show no pathology change in routine histological examinations, a quantitative histological study and electron microscopic ultrastructural analysis have detected the enlarged space among epithelial cells and cytoskeletal cohesion in the intestinal mucosa of D-IBS patients (8), which may result from aberrant synthesis of tight junction protein 1 (claudin-1) that plays a significant role in regulating the osmotic pressure of intestinal mucosa.