Taking into account the results on serum zonulin concentration from previous studies conducted at our Center on IBD patients, we observed that serum zonulin concentration in patients with IBS-D was comparable to that found in patients with IBD (43.3 (95% CI 37.3–46.4) vs. 45.3 (95% CI 43.5–47.8) ng/mL, respectively) [30] and higher than those found in healthy controls (8.6 (95% CI 7.2–10.5) ng/mL) [8]. The gene discussed is HP; the disease is inflammatory bowel disease.