Recently in Gut and elsewhere, rare and common hypomorphic sucrase-isomaltase (SI) gene variants have been linked to an increased risk of IBS. Similar to congenital SI deficiency (a form of carbohydrate malabsorption caused by homozygous SI loss-of-function mutations), reduced SI enzymatic activity may trigger IBS symptoms via colonic accumulation of undigested disaccharides from starch and sucrose, resulting in fermentation with gas production and osmotic diarrhoea. This information holds potential for patients’ stratification, and the identification of IBS subgroups better suited to benefit from specific dietary restrictions. For instance, diets low in short chain carbohydrates like the FODMAPs (fermentable oligo-, di-, mono-saccharides and polyols that are poorly absorbed in the small intestine) have been shown to be effective in reducing GI symptoms in some patients with IBS, though this has not been studied in relation to SI genotype and/or function. While sucrose and, in part, starch are not specifically restricted in a standard low FODMAP diet, such a therapeutic approach may be less effective in individuals whose reduced SI activity contributes to symptoms. Hence, a low FODMAP diet may be less effective in patients with IBS carrying SI hypomorphic variants.
- genetic polymorphisms
- irritable bowel syndrome