How is Genetic Sucrase-Isomaltase Deficiency/Congenital Sucrase-Isomaltase Deficiency Diagnosed?

The diagnosis of Genetic Sucrase-Isomaltase Deficiency/Congenital Sucrase-Isomaltase Deficiency can be missed, especially if patients have mild, nonspecific symptoms. Correct Genetic Sucrase-Isomaltase Deficiency diagnosis may be delayed while other causes of severe, chronic diarrhea are entertained. 1

Commonly, patients are misdiagnosed with food allergy or intolerance to cow’s milk or soy protein. An improvement in symptoms while ingesting a casein-hydrosylate formula may be interpreted as support for this mistaken diagnosis, when it, in fact, reflects the switch from carbohydrate to glucose polymers, which are dependent on glucoamylase activity for digestion.2 Once infancy is passed and a larger variety of foods are added to the diet, it is increasingly difficult to correctly identify sucrose as the explicit cause of symptoms. In addition, there may be high co-morbidities between Genetic Sucrase-Isomaltase Deficiency and other enzymatic deficiencies involved in carbohydrate digestion.

Such co-morbidities and/or misdiagnoses may include allergic gastroenteropathy, cystic fibrosis, celiac disease, severe viral gastroenteritis, lactose intolerance, glucose-galactose intolerance or other causes of intractable diarrhea. Mild steatorrhea is commonly used to support these diagnoses. 3

As the table below indicates, there are several tests that may help in the diagnosis of GSID/CSID.

Testing Methods to Aid in the Diagnosis of Genetic Sucrase-Isomaltase Deficiency (GSID)

Test Method
Info Regarding Test Method
Disaccharidase Assay
  • Gold standard for diagnosing GSID
  • Additional tissue sample is obtained from the distal duodenum or proximal jejunum at the time of endoscopy
  • Assay is only performed by a certain number of labs
Sucraid® Therapeutic Trial
  • Sucrase enzyme replacement therapy
  • A 2-week sample of a medication called Sucraid®, which is an exogenous enzyme
Free Sucrose Breath Test
  • The test is noninvasive, short in duration and capable of being administered by the patient at home
  • A healthcare professional can order the test by calling 1-800-705-1962
  • Patients follow the simple test instructions included in each kit and ship the test kit back via a pre-paid shipping label. Test results will be provided to the physician’s office within 24 hours of receiving the test kit
  • Patients with sucrase deficiency may experience symptoms due to the large consumption of sucrose
13C Sucrose Breath Test
  • Noninvasive
  • Newer procedure
  • Requires fasting for at least 3 hours
  • Must fill breath bags over a 3-hour time period after ingestion of sucrose and glucose
  • Mass spectrometry
  • Specific test for Genetic Sucrase-Isomaltase Deficiency
  • Does not produce symptoms in Genetic Sucrase-Isomaltase Deficiency patients because it does not require excessive consumption of sucrose
Stool pH Test
  • An indirect test for carbohydrate malabsorption
  • Not specific for sucrose malabsorption
Free SI Genetic Test
  • When sucrase activity is <25 μM/min/g
  • If disaccharidase assay results are not available for patients with long-term chronic diarrhea and/or abdominal pain, and other common GI disorders have been excluded
  • To order an SI Genetic Test kit call 1-800-705-1962
  • A positive genetic test supports the diagnosis of GSID. The test evaluates for the presence of 37 known pathogenic variants
  • A negative test result demonstrates the absence of one or more of these variants. However, other unidentified pathogenic variants may exist, so a negative test is not conclusive for absence of the disease
4-4-4 Simple Oral Sugar Challenge
  • The test is short, simple and can be performed in the privacy of the patient’s home
  • Step 1: Stir 4 tablespoons of ordinary table sugar into a 4-ounce glass of water. Mix until sugar is completely dissolved
  • Step 2: Drink it on an empty stomach
  • Step 3: See if symptoms such as bloating, gas and diarrhea occur during the next 4-8 hours; this suggests sucrose intolerance is possible

 What are the Treatment Options?

In patients with Genetic Sucrase-Isomaltase Deficiency/Congenital Sucrase-Isomaltase Deficiency and overt symptoms that warrant treatment, three major treatment options exist: nonpharmacologic, pharmacologic or a combination of both. Before the advent of specific pharmacologic treatment, the treatment of Genetic Sucrase-Isomaltase Deficiency consisted of lifelong adherence to a strict sucrose-free diet. However, given the sucrose content of Western diets, patient compliance with a sucrose-free diet is, at best, difficult. Patient noncompliance is common and often accompanied by continued chronic gastrointestinal symptoms, decreased weight for height and decreased weight for age. 4 5 6 In fact, in a clinical trial testing a restricted diet, 75% of patients were not asymptomatic.5

Enzyme replacement therapy with Sucraid® offers a pharmacologic alternative to sucrose-free diets. Sucraid® is an effective option for the management of sucrase deficiency that reduces or eliminates both the need for dietary restrictions of sucrose and the symptoms of Genetic Sucrase-Isomaltase Deficiency in the majority of patients. 7 In long-term clinical trials, 81% of Sucraid® patients became asymptomatic.8 Note that Sucraid® does not provide specific replacement therapy for the deficient isomaltase.9 Therefore, restricting starch in the diet may still be necessary to reduce symptoms as much as possible. The need for dietary starch restriction for patients using Sucraid® should be evaluated in each patient.

In long-term clinical trials, 81% of Sucraid® patients became asymptomatic.

Given the demonstrated efficacy of Sucraid® (sacrosidase) Oral Solution in correcting sucrase deficiency, a short therapeutic trial (e.g., two weeks) may be warranted to assess the response of a patient with suspected sucrase deficiency.9 Substantial attenuation or elimination of symptoms while the patient is on a normal, sucrose-containing diet suggests the presence of Genetic Sucrase-Isomaltase Deficiency.


  1. Ament ME, Perera DR, Esther LJ. Sucrase-isomaltase deficiency – a frequently misdiagnosed disease. J Pediatr. 1973;83:721-727.
  2. Treem WR. Congenital sucrase-isomaltase deficiency. J Pediatr Gastroenterol Nutr. 1995;21:1-14.
  3. Gudmand-Hoyer E, Krasilnikoff PA, Skovberg H. Sucrose-isomaltose malabsorption. In: Draper H, ed. Advances in nutritional research; vol 6. New York: Plenum Press, 1984:233-269.
  4. Antonowicz I, Lloyd-Still JD, Khaw KT, Shwachman H. Congenital sucrase-isomaltase deficiency. Observations over a period of 6 years. Pediatrics. 1972;49:847-853.
  5. Gudmand-Hoyer E. Sucrose malabsorption in children: a report of thirty-one Greenlanders. J Pediatr Gastroenterol Nutr. 1985;4:873-877.
  6. Kilby A, Burgess EA, Wigglesworth S, Walker-Smith JA. Sucrase-isomaltase deficiency. A follow-up report. Arch Dis Child. 1978;53:677-679.
  7. Naim HY, Roth J, Sterchi EE, et al. Sucrase-isomaltase deficiency in humans. Different mutations disrupt intracellular transport, processing, and function of an intestinal brush border enzyme. J Clin Invest. 1988;82:667-679.
  8. Treem WR, McAdams L, Stanford L, Kastoff G, Justinich C, Hyams J. Sacrosidase therapy for congenital sucrase-isomaltase deficiency. J Pediatr Gastroenterol Nutr. 1999;28:137-142.
  9. Sucraid® (sacrosidase) Oral Solution Full Prescribing Information.
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