About GSID and CSID

What is Genetic Sucrase-Isomaltase Deficiency/Congenital Sucrase-Isomaltase Deficiency?


Genetic Sucrase-Isomaltase Deficiency/Congenital Sucrase-Isomaltase Deficiency is a rare disorder that affects a person’s ability to digest certain sugars due to absent or low levels of two digestive enzymes, sucrase and isomaltase.1 Sucrase and isomaltase are involved in the digestion of sugar and starch. Sucrase is an enzyme produced in the small intestine that aids in the breakdown of sucrose (table sugar) into glucose and fructose, which are used by the body as fuel. Isomaltase is one of several enzymes that helps digest starches.

Genetic Sucrase-Isomaltase Deficiency/Congenital Sucrase-Isomaltase Deficiency is also known as SI Deficiency, Disaccharide Intolerance I and Congenital Sucrose Intolerance. This disorder is equally prevalent in males and females.

Failure to absorb dietary sucrose and starch may impact the absorption of other nutrients and the hormonal regulation of gastrointestinal function. Unabsorbed carbohydrates inhibit gastric emptying, accelerate small-intestinal transit and contribute to malabsorption of starch, fat and monosaccharides. Patients with Genetic Sucrase-Isomaltase Deficiency are at risk for chronic malnutrition; indeed, failure to thrive is one of the characteristics of the disease state. In addition to diarrhea, some patients suffer from gassiness, abdominal distention and pain.

Sucrose cannot be absorbed in its native form and is useless as an energy source unless it is metabolized to the monosaccharide subunits, glucose and fructose.2

© The McGraw-Hill Companies, Inc.


  1. Treem WR. Clinical heterogeneity in congenital sucrase-isomaltase deficiency. J Pediatr. 1996;128:727-729.
  2. Gray GM. Carbohydrate digestion and absorption. Role of the small intestine. N Engl J Med. 1975;292:1225-1230.
This site is for U.S. Residents Only
QOL Medical, LLC

Are you a healthcare professional?

Yes No