What is CSID?

Congenital Sucrase-Isomaltase Deficiency (CSID), more commonly known as Sucrose Intolerance or carbohydrate malabsorption, is a rare, autosomal genetic disorder characterized by the diminished activity of two digestive enzymes, sucrase and isomaltase. CSID reduces one’s ability to digest sucrose and dietary starches into the absorbable form of monosaccharides. Sucrose, also called table sugar, is found naturally in many fruits and vegetables, and is often added to processed foods.

The lifelong symptoms of CSID are caused by fermentation of the unabsorbed sugars. They include chronic postprandial diarrhea, excess gas, bloating, and abdominal cramps. Infants with CSID typically experience caustic diaper rash and failure to thrive. The clinical symptoms of CSID are shared by several common GI conditions, often making it difficult to diagnose.

How is CSID Diagnosed?

As is common in the practice of gastroenterology, healthcare providers combine information gleaned from a patient’s medical and family history and presenting symptoms with results from a diagnostic test to reach a probable CSID diagnosis. Typically, the probable diagnosis of CSID can be confirmed when a patient has a positive response to the indicated treatment for CSID.

Among the diagnostic tests a physician may perform to aid in reaching a probable CSID diagnosis, the most common office- or home-based tests are breath tests. These can be either hydrogen-methane or 13C-sucrose breath tests which quantify the metabolic byproducts of sucrose digestion in exhaled air. A simper test may detect CISD based on the GI response to drinking a concentrated sugar solution. This is referred to as the 4-4-4 test, for drinking a solution of 4 tablespoons of sugar dissolved in 4 ounces of water and observing the GI response for 4 hours.