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Congenital Sucrase-Isomaltase Deficiency
Saturday, 22 September 2007
Monday, 29 November 1999
CSID, Disaccharide Intolerance


Congenital Sucrase-Isomaltase Deficiency, or CSID, is a disease caused by a genetic defect that leads to chronic watery diarrhea and growth failure in infants and toddlers.


This disease can affect anyone but most often occurs in the Native populations of Canada, Alaska, and Greenland; in these populations, approximately 3-10% of the children may be affected with this disorder.  In the general North American population, approximately 0.2% of the population may have this deficiency.  It affects males and females equally.  The disease is inherited in an autosomal recessive fashion, which means that both the father and mother must be carriers of the mutated gene, and that they each give the defective gene copy to their child, who then has the disease.  It is important to distinguish CSID (caused by a gene mutation) from acquired or secondary causes of sucrase-isomaltase deficiency, which is more common and may be caused by HIV infection, gastroenteritis, or short gut syndrome. 

Signs and Symptoms

These patients begin having diarrhea when they are introduced to fruits and juices as early as 6 months of age.  Most commonly, the diarrhea is watery and non-bloody, and the patients exhibit growth failure.  Other findings may also include abdominal distension, abdominal pain, muscle wasting, weakness, irritability, excessive gassiness, diaper rash (from the recurrent diarrhea and from poor nutrition), and occasionally even vomiting.

Possible Causes

Most CSID patients have a mutation of a gene on chromosome 3 that normally leads to production of the sucrase-isomaltase enzyme complex.  Some people will also have a mutation on chromosome 7 which contributes to the disease, though not all patients will have both mutations.  The enzyme complex is normally found in the lining of the small intestine and is responsible for breaking down complex sugars like sucrose (table sugar).  These sugars are commonly found in fruits and juices.  If patients cannot break down these sugars, they pass through the small intestine, undigested, and produce a watery diarrhea.  With excessive diarrhea, other nutrients are not well-absorbed because they will also pass through the intestines too rapidly, and sugars that would otherwise be used for calories and growth are lost in the stool.  As mentioned above, the disease is inherited in an autosomal recessive manner, so both (unaffected) parents must each have a mutation in one copy of the gene that codes for the sucrase-isomaltase enzyme complex, and they must each pass that defective copy to their offspring, who then manifests with the disease. 


Diagnosis of CSID is made by a careful assessment of clinical history, family history, physical examination, and some complicated laboratory tests.  Other causes for chronic diarrhea need to be eliminated, such as infections, cystic fibrosis, or other organ-based causes like the heart or liver.  The definitive test for CSID is to take a biopsy of the small intestine while performing an upper endoscopy and to test for the activity of the enzyme that is affected.  This biopsy also allows for microscopic examination of the small intestinal tissue to rule out other possible causes for diarrhea.  Other tests include checking a breath hydrogen test (which is increased in these patients) and checking the pH of the stool (which is generally acidic, ranging from 5-6).  Occasionally, conducting a biopsy and testing for the activity of the affected enzyme is not possible, and the diagnosis is made based upon specific breath tests and stool studies alone; however, the best and most definitive test is to have a biopsy.  At this time, genetic testing of the parents for the mutations in chromosome 3 is not available.


Treatment of this disorder consists of a strict, lifelong, sucrose-free diet.  This diet can be very difficult to follow, given the number of foods that contain sucrose and other complex sugars.  Recently, a novel treatment approach has been developed which involves taking a medication called Sucraid.  Sucraid is an oral medication containing the enzyme that has been mutated in this disorder. Therefore, CSID patients can then eat sucrose-containing foods, with this enzyme digesting the food appropriately.  This has led to a dramatic reduction in symptoms for these patients such that they are able to eat an essentially normal diet as long as they take the medicine with each meal or snack. 


Prior to the advent of Sucraid, patients were faced with a difficult diet to follow.  However, now that this medication is available, patients can expect to do very well, without significant complications or an increased risk for other diseases or malnutrition.  It is important to recognize that the disease is life-long, and that patients will need to take this medicine for the remainder of their lives, or alternatively, adhere to the strict sucrose-limiting diet. 

Connect with other parents

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Congenital Sucrase-Isomaltase Deficiency

A very nice website with links to physicians who specialize in this disorder, links to support groups, and guidelines for a sucrose-free diet. 

Isbbio2 at wikispaces

More information about this disorder. 

Google Search for Congenital Sucrase-Isomaltase Deficiency

References and Sources

Sucraid Review. US Consumer Product Safety Commission. April. 1998.

Treem WR, McAdams L, Stanford L, et al. Sacrosidase therapy for congenital sucrase-isomaltase deficiency. J Ped Gastro Nutr. 1999;28(2):137-142

Mahant S, Friedman J. "Index of Suspicion, Case 3", Pediatrics in Review 2000; 21(1):24-25.