Sucrase Isomaltase Deficiency

The goal of this interventional study is to examine whether those patients with irritable bowel syndrome (IBS) and a reduced abitility do degrade starch and sugar (lowe levels of enzymes) have lower raise in blood glucose after a meal than those with normal expression of enzymes. We also want to examine whether those IBS patients with reduced enzyme levels have increased bowel symptom in relation to this meal. The main questions it aims to answer are: Does reduced ability to degrade starch and sugar due to less enzyme activity lead to lower increase in blood glucose after a meal? Does reduced ability to degrade starch and sugar due to less enzyme activity lead to increased bowel symptoms after a meal?

Irritable bowel syndrome (IBS) affects one in seven people with gastrointestinal (GI) symptoms that are detected without an established underlying organic cause. IBS strongly impacts quality of life, is a leading cause of work absenteeism, and consumes 0.5% of the healthcare annual budget. It manifests in women more than men with symptoms including abdominal pain, bloating, constipation (IBS-C), diarrhoea (IBS-D), and mixed presentations (IBS-M). The development of therapeutic options is hampered by the heterogeneity of IBS, the lack of specificity of its symptom-based definitions, and the poor understanding of the underlying pathophysiological mechanisms. Many people with IBS find that certain foods (particularly carbohydrates) trigger their symptoms and avoiding such foods has been shown to be effective in IBS. An example of such a diet is the low-FODMAP (fermentable oligo-, di-, monosaccharides and polyols) exclusion diet, developed by researchers at Monash University. This has suggested that the food-symptom relation may involve malabsorption of carbohydrates due to inefficient enzymatic breakdown of polysaccharides. However, only a percentage of subjects respond to this diet. Overall, the current findings relating to SI, suggest a strong potential for effective personalized therapeutic (dietary) interventions in subgroups of IBS subjects and suggest similar mechanisms should be investigated in relation to other genes involved in the digestion and absorption of carbohydrates (CDGs). This project aims to understand what the mechanisms for GI symptoms in subjects with these genetic alterations are. Aim of the study is to assess the gut response to a sucrose challenge in single-and double-carriers of the common hypomorphic sucrase-isomaltase variant p. (Val15Phe) vs non- carriers (negative controls) and CSID subjects (positive controls), applying an MRI multiparametric test combined with a breath test.

Irritable bowel syndrome (IBS) is a functional disorder causing troublesome symptoms and reduced quality of life. It affects 10-20% of the population, hence creates large costs for society. About 30-40% of all IBS patients do not benefit from current treatment options. Sucrase-isomaltase (SI) deficiency is an unexplored condition, that may explain symptoms in IBS patients who experience no effect from today's treatments. Currently, a duodenal biopsy is the gold standard for the diagnosis of SI deficiency, however the condition is not well investigated. A 13C-labelled breath test holds promise as a non-invasive alternative, but it has not previously been validated. This project will address the knowledge gap related to a possible association between SI deficiency and IBS by addressing two research questions that have never been answered before. We aim to: 1. Validate the 13C-labelled breath test as a diagnostic tool by assessing the strength of the association between the breath test and SI activity measured in duodenal biopsies 2. Use the 13C-labelled breath test in a randomized dietary crossover trial comparing a starch and sucrose reduced diet (SSRD) with the standard low-FODMAP diet in IBS patients, to evaluate whether SI activity is associated with dietary changes according to symptom severity and gut microbiota composition