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Congenital sucrase-isomaltase deficiency


Congenital sucrase-isomaltase deficiency is a rare genetic disorder that affects an individual's ability to digest certain sugars. People with this condition cannot break down the sugars sucrose and maltose. Sucrose (a sugar found in fruits, and also known as table sugar) and maltose (the sugar found in grains) are called disaccharides because they are made of two simple sugars. Disaccharides are broken down into simple sugars during digestion. Sucrose is broken down into glucose and another simple sugar called fructose, and maltose is broken down into two glucose molecules. People with congenital sucrase-isomaltase deficiency cannot break down the sugars sucrose and maltose, and other compounds made from these sugar molecules (carbohydrates).

Congenital sucrase-isomaltase deficiency usually becomes apparent after an infant is weaned and starts to consume fruits, juices, grains, and other starchy food. After ingestion of sucrose or maltose, an affected individual will typically experience stomach cramps, bloating, excess gas production, and diarrhea. These digestive problems can lead to failure to gain weight and grow at the expected rate (failure to thrive) and malnutrition.


The prevalence of congenital sucrase-isomaltase deficiency is estimated to be 1 in 5,000 people of European descent. This condition is much more prevalent in the native populations of Greenland, Alaska, and Canada, where as many as 1 in 20 people may be affected.


Variants (also known as mutations) in the SI gene cause congenital sucrase-isomaltase deficiency. The SI gene provides instructions for producing the enzyme sucrase-isomaltase. This enzyme is found in the small intestine and is responsible for breaking down sucrose and maltose into their simple sugar components. These simple sugars are then absorbed by the small intestine. Variants that cause this condition alter the structure, disrupt the production, or impair the function of sucrase-isomaltase. These changes prevent the enzyme from breaking down sucrose and maltose. Rather than being absorbed by the small intestine, the undigested sugars move to the large intestine (colon). Here, they attract water and are consumed by normal bacteria in the colon, causing  the intestinal discomfort seen in individuals with congenital sucrase-isomaltase deficiency.


Congenital sucrase-isomaltase deficiency is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have variants. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they may not show signs and symptoms of the condition.

Other Names for This Condition

  • Congenital sucrose intolerance
  • Congenital sucrose-isomaltose malabsorption
  • CSID
  • Disaccharide intolerance I
  • SI deficiency
  • Sucrase-isomaltase deficiency

Additional Information & Resources

Genetic and Rare Diseases Information Center

Patient Support and Advocacy Resources

Clinical Trials

Catalog of Genes and Diseases from OMIM

Scientific Articles on PubMed


  • Belmont JW, Reid B, Taylor W, Baker SS, Moore WH, Morriss MC, Podrebarac SM, Glass N, Schwartz ID. Congenital sucrase-isomaltase deficiency presenting with failure to thrive, hypercalcemia, and nephrocalcinosis. BMC Pediatr. 2002 Apr 25;2:4. doi: 10.1186/1471-2431-2-4. Citation on PubMed or Free article on PubMed Central
  • Husein DM, Wanes D, Marten LM, Zimmer KP, Naim HY. Heterozygotes Are a Potential New Entity among Homozygotes and Compound Heterozygotes in Congenital Sucrase-Isomaltase Deficiency. Nutrients. 2019 Sep 25;11(10):2290. doi: 10.3390/nu11102290. Citation on PubMed
  • Jacob R, Zimmer KP, Schmitz J, Naim HY. Congenital sucrase-isomaltase deficiency arising from cleavage and secretion of a mutant form of the enzyme. J Clin Invest. 2000 Jul;106(2):281-7. doi: 10.1172/JCI9677. Citation on PubMed or Free article on PubMed Central
  • Keiser M, Alfalah M, Propsting MJ, Castelletti D, Naim HY. Altered folding, turnover, and polarized sorting act in concert to define a novel pathomechanism of congenital sucrase-isomaltase deficiency. J Biol Chem. 2006 May 19;281(20):14393-9. doi: 10.1074/jbc.M513631200. Epub 2006 Mar 16. Citation on PubMed
  • Naim HY, Roth J, Sterchi EE, Lentze M, Milla P, Schmitz J, Hauri HP. Sucrase-isomaltase deficiency in humans. Different mutations disrupt intracellular transport, processing, and function of an intestinal brush border enzyme. J Clin Invest. 1988 Aug;82(2):667-79. doi: 10.1172/JCI113646. Citation on PubMed
  • Ouwendijk J, Moolenaar CE, Peters WJ, Hollenberg CP, Ginsel LA, Fransen JA, Naim HY. Congenital sucrase-isomaltase deficiency. Identification of a glutamine to proline substitution that leads to a transport block of sucrase-isomaltase in a pre-Golgi compartment. J Clin Invest. 1996 Feb 1;97(3):633-41. doi: 10.1172/JCI118459. Citation on PubMed
  • Ritz V, Alfalah M, Zimmer KP, Schmitz J, Jacob R, Naim HY. Congenital sucrase-isomaltase deficiency because of an accumulation of the mutant enzyme in the endoplasmic reticulum. Gastroenterology. 2003 Dec;125(6):1678-85. doi: 10.1053/j.gastro.2003.09.022. Citation on PubMed
  • Sander P, Alfalah M, Keiser M, Korponay-Szabo I, Kovacs JB, Leeb T, Naim HY. Novel mutations in the human sucrase-isomaltase gene (SI) that cause congenital carbohydrate malabsorption. Hum Mutat. 2006 Jan;27(1):119. doi: 10.1002/humu.9392. Citation on PubMed
  • Sibley E. Carbohydrate intolerance. Curr Opin Gastroenterol. 2004 Mar;20(2):162-7. doi: 10.1097/00001574-200403000-00019. Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.