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Abstract

Background: Patients with irritable bowel syndrome (IBS) often report symptoms following lactose ingestion. We found that in spite of similar frequency of lactose malabsorption (LM) and breath hydrogen levels, patients with IBS developed symptoms more commonly than healthy controls, which might be due to visceral hypersensitivity. Hence, we aimed to study; level of serotonin and SERT polymorphism among patients with IBS who developed symptoms following lactose ingestion compared to those who did not develop it. Method: 150 patients with IBS (Rome III criteria) were evaluated for symptom development following lactose ingestion. Serotonin was estimated on rectal biopsy (ELISA) and SERT polymorphism studied on DNA extracted from venous blood (PCR). Results: Of 150 patients (age 36.7±11.8-y, 114 [76%] male), 62 (41.3%) developed symptoms following lactose and 88 (58.7%) did not. Serotonin level in rectal tissue was higher among patients with IBS who developed symptoms compared to those who did not (144.8±40.9 vs. 122.7±36.3-pmol/mL, p=0.001). Also, patients with IBS who developed symptoms following lactose ingestion had higher frequency of deletion/deletion (s/s) SERT genotype compared to those who did not [s/s 48/62 (77.4%), s/l 8/62 (12.9%), l/l 6/62 (9.7%) vs. s/s 41/88 (46.6%), s/l 36/88 (40.9%), l/l 11/88 (12.5%), p=0.003, respectively]. Patients with IBS who had deletion/deletion genotype had higher level of serotonin in rectal tissue compared to deletion/insertion and insertion/insertion genotypes (151.1±37.3 vs. 105.0±20.9 vs. 100.9±28.0 pmol/ mL, p<0.001, respectively). Conclusion: Symptom development in patients with IBS following lactose ingestion is related to higher serotonin level in rectal tissue and SERT gene polymorphism.

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