Short answer · Medically reviewed summary · Last updated: 2026-05-08
Congenital Sucrase-Isomaltase Deficiency (CSID) is a genetic disorder caused by mutations in the SI gene, which prevents the body from producing the necessary enzymes to break down sucrose and maltose. Because the small intestine cannot digest these sugars, they remain in the gut, leading to the gastrointestinal symptoms characteristic of this condition. What causes Congenital Sucrase-Isomaltase Deficiency? The primary cause of Congenital Sucrase-Isomaltase Deficiency is a dysfunction in the SI gene located on chromosome 3.
2 people with Congenital Sucrase Isomaltase Deficiency have shared their first-person experience on this question at DiseaseMaps.
Which are the causes of Congenital Sucrase Isomaltase Deficiency?
Causes of Congenital Sucrase Isomaltase Deficiency explained: genetic and environmental factors, reviewed against medical sources, plus patient perspectives.
Congenital Sucrase-Isomaltase Deficiency (CSID) is a genetic disorder caused by mutations in the SI gene, which prevents the body from producing the necessary enzymes to break down sucrose and maltose. Because the small intestine cannot digest these sugars, they remain in the gut, leading to the gastrointestinal symptoms characteristic of this condition.
What causes Congenital Sucrase-Isomaltase Deficiency?
The primary cause of Congenital Sucrase-Isomaltase Deficiency is a dysfunction in the SI gene located on chromosome 3. This gene provides instructions for creating the sucrase-isomaltase enzyme complex. When this gene is mutated, the enzyme is either not produced, not transported to the surface of the intestinal cells, or is functionally defective. You can think of the enzyme as a "chemical key" that unlocks complex sugars so they can be absorbed into the bloodstream; in Congenital Sucrase-Isomaltase Deficiency, the lock is either missing or the key is broken, leaving undigested sugars to ferment in the colon.
Is Congenital Sucrase-Isomaltase Deficiency hereditary?
Yes, Congenital Sucrase-Isomaltase Deficiency is an autosomal recessive disorder. This means that an individual must inherit two copies of the mutated SI gene—one from each parent—to manifest the condition. Parents who each carry one copy of the mutation are typically asymptomatic, but they have a 25% chance of passing the condition to each child.
Are there environmental triggers or other mechanisms?
While the root cause is genetic, the severity of symptoms in Congenital Sucrase-Isomaltase Deficiency is heavily influenced by diet. Environmental triggers include the ingestion of sucrose (table sugar) and starch, which exacerbate symptoms like osmotic diarrhea, bloating, and abdominal pain. Unlike autoimmune diseases, Congenital Sucrase-Isomaltase Deficiency is not caused by the immune system attacking the body, nor is it an infectious disease.
What does current research reveal about the etiology?
Researchers are currently studying the wide spectrum of SI gene mutations to understand why some patients experience milder symptoms than others. Current clinical literature focuses on:
- Identifying specific "hotspot" mutations within the SI gene.
- Developing diagnostic biomarkers to distinguish Congenital Sucrase-Isomaltase Deficiency from other conditions like Irritable Bowel Syndrome (IBS).
- Investigating the prevalence of heterozygous carriers in the general population, which is estimated to be as high as 1 in 20 to 1 in 50 individuals in some ethnic groups.
Next steps
- Consult a gastroenterologist or a registered dietitian who specializes in disaccharidase deficiencies.
- Request a disaccharidase assay via an intestinal biopsy or genetic testing to confirm the diagnosis.
- Join the 140 members of the DiseaseMaps community living with Congenital Sucrase-Isomaltase Deficiency to share management strategies.
Medical disclaimer: This content is for educational purposes only and does not constitute professional medical advice, diagnosis, or treatment.
References
- NIH Genetic and Rare Diseases Information Center (GARD): Congenital sucrase-isomaltase deficiency.
- Online Mendelian Inheritance in Man (OMIM): Sucrase-Isomaltase Deficiency; SID.
- Orphanet: Congenital sucrase-isomaltase deficiency (ORPHA:867).
- PubMed/NCBI: Clinical and genetic insights into SI gene mutations.
The cause of the symptoms is a lack of the enzyme 'Sucrase' which breaks down the disaccharide 'Sucrose' into monosaccharides. Monosaccharides can be absorbed into the body in the intestine, disaccharides cannot. The undigested sugars(disaccharides) ferment in the intestine causing pain, gas, bloating leading to diarrhoea.
Similarly a lack of the enzyme 'Isomaltase' which breaks down starch into smaller parts for absorption causes the same symptoms.
Posted Mar 8, 2019 by Simone 3215
Posted Nov 15, 2021 by Tracey 3000
