Background: Serotonin (5-HT) release and serotonin reuptake transporter (5-HTT) expression have been reported to be decreased in experimental colitis, in interleukin-10 knockout-associated colitis, and in patients with ulcerative colitis. Serotonin is known to play an important role in the pathogenesis of colitis, but individual genetic variants of 5-HTT gene in microscopic colitis and ulcerative colitis are not known.
Aim: This study aimed to evaluate the association between the serotonin transporter gene promoter polymorphism (5-HTTLPR) and 5-HT concentration in microscopic colitis (MC) and ulcerative colitis (UC) patients.
Method: This prospective case-control study included 41 patients with microscopic colitis (age 19-82 years, mean 35 ± 13.6), 75 patients with ulcerative colitis (age 16-65 years, mean 38.5 ± 11.6), and 100 controls (age 20-64 years, mean 38 ± 11). 5-HTTLPR gene polymorphism was studied by polymerase chain reaction-based assay. 5-HT levels were measured by ELISA.
Results: The frequency of the 5-HTTLPR (SS) genotype was significantly lower in MC (12 %) patients compared to controls (30 %) (p < 0.05). When the L/L and L/S genotypes were combined into one group, the frequencies of the non-S genotype were significantly higher than those of S/S genotype between the MC patients and the controls (p < 0.05). 5-HT levels were significantly higher in UC and MC patients compared to healthy controls (p < 0.01).
Conclusions: A significant association was observed between LL genotype of 5-HTTLPR polymorphism and microscopic colitis, suggesting that 5-HTTLPR is a potential candidate gene involved in the pathogenesis of microscopic colitis. Serotonin levels were significantly higher in microscopic colitis and ulcerative colitis patients compared to healthy controls.