The prevalence of TPH1 gene polymorphisms, including rs211105 and rs453771, did not differ between patients with IBS and healthy subjects.(20,28) Furthermore, in a meta-analysis, no significant difference was detected in the prevalence of 5-HTTLPR variation between patients with IBS and healthy controls.(29) Considering the results of past studies and this study, the polymorphisms of SERT and TPH1 in patients with IBS-D seem not crucial to the onset of IBS-D but is a possible factor that modifies GI symptoms and mental status in Japanese patients. This evidence concerns the gene SLC6A4 and irritable bowel syndrome.