Sucrase-isomaltase genotype and response to a starch-reduced and sucrose-reduced diet in IBS-D patients
Recently in Gut, several reviews and reports have highlighted hypomorphic (dysfunctional) variants of the sucrase-isomaltase (SI) gene in relation to increased risk of irritable bowel syndrome (IBS), particularly the diarrhoea-predominant type (IBS-D).1–4 Similar to congenital (rare recessive) and acquired forms of SI deficiency, impaired SI enzymatic activity is expected to lead to colonic accumulation of undigested disaccharides, thus triggering IBS manifestations via gut microbiota fermentation, gas production and osmotic diarrhoea. Reduced efficacy of a diet low in FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) is also observed for SI hypomorphic IBS-D carriers,4 as this intervention may be suboptimal for individuals with possible defects in the digestion of carbohydrates other than FODMAPs (the lowFODMAP diet does not specifically restrict sucrose and starch, the substrates of SI disaccharidase activity). These results hold strong potential for personalising therapeutic (dietary) interventions in subgroups of IBS patients, though the eventual relevance of SI genotype has not been tested in the optimal dietary context, that is when patients are challenged with reducing the amount of SI substrates, like in a sucrose and starch-restricted diet (SSRD).
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