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Introduction

This information is being provided for those who have been diagnosed with Congenital Sucrase-Isomaltase Deficiency (CSID), caretakers of children with CSID, and physicians and dieticians who need information on CSID. 

Although every effort has been made to insure the accuracy of the information by collaborating with doctors researching and treating the disorder, dietitians, and pharmacists you will still need to seek competent medical advise regarding all information provided. All the information provided on this website has been reviewed by doctors at the University of Washington Medical Center and their dietitians for use by physicians. We are a registered member of NORD.

Alternative Names Given to the Disorder

Congenital Sucrase-Isomaltase Deficiency is also known as Disaccharide Intolerance I, SI Deficiency, Congenital Sucrose Intolerance and CSID. 

Total Known Diagnosed to Date Worldwide: 7512 children and adults. We do not include counts for Iceland, Greenland and Alaska.

Brief Discussion

If you are a patient, or a caretaker of a patient, trying to research the disorder it may feel overwhelming because very little is written about the disorder in lay-person terms.   Sucrase-Isomaltase Deficiency results from either an inherited condition or by an injury to the digestive system.  This website focuses on the inherited condition (CSID).

CSID results from a child inheriting two recessive genes on the autosomal (non-sex-determining) chromosome number 3. One recessive gene provided from the mother and the other from the father. Males and females are affected with equal frequency.  This can occur even if there is no previous family history of the disorder (i. e. when two non-symptomatic parents who are both carriers of the particular recessive gene have a child). This is an active recessive disorder, meaning carriers will also have symptoms but to a lesser degree and may be misdiagnosed with other bowel disorders.

Homozygotes (2 recessive genes) have severe enzyme deficiency with clinical symptoms throughout life. Unlike the literature we have no reported cases of children with mutations A, and D having symptoms improve over time. Some children with mutation B show improvement in starch consumption between ages 1 year and 3-1/2 as the bowel matures. A few children in group C have reported the ability to consume as much as seven grams of sucrose/100 grams of food without the need for Sucraid during their teen years, but symptoms reoccur or worsen again between the ages of 27 to 40. We are also documenting a statically significant higher than normal occurrence of colon cancer in adults who were not diagnosed until later in life who have consumed normal levels of sucrose and starch, and in their parents, grand-parents, and aunts and uncles; this is particularly true of mutations A and C.

Heterozygotes (carriers - 1 recessive gene) have intermediate enzyme values, mild symptoms in infancy and childhood and some milder symptoms in adulthood.  It is believed that as many as 10% of Greenland Eskimos and possibly equally as high percentage of Alaskan Eskimos have CSID. 

Potential Carriers Include:

This disorder is most commonly found among those with the following ethnic backgrounds:

Introductory Description of CSID

All CSID patients lack an enzyme called sucrase.  Some also have varying degrees of activity of another enzyme called isomaltase.  Sucrase-isomaltase is an integral protein of the small intestine brush border membrane responsible for triggering the metabolism of dietary sucrose and the final products of starch digestion.   It is believed that some people with this disorder can consume starch without becoming  symptomatic in part because isomaltase activity varies according to the mutation of the gene structure. There are now four emerging populations of children and adults with this disorder each with their own set of symptoms and tolerances for sucrose, starch and lactose. These groups are discussed in our Symptoms portion of the website.

Usually when a child or adult ingests sucrose (which requires the sucrase enzyme for digestion) the individual will become symptomatic. A deficiency of the enzyme results primarily in osmotic diarrhea when the disaccharide (sucrose in this case) is ingested, because absorption cannot occur until after hydrolysis produces the component monosaccharides (simple sugars).   Additional factors, such as the total amount of ingested sucrose, the rate of gastric emptying, the ability of the small intestine to handle the osmotic load, the metabolic activity of colonic bacteria and the ability of the colon to absorb water and short-chain fatty acids.  To varying degrees, children who ingest starches high in amylopectin such as wheat, potatoes, and corn sweeteners (which require isomaltase for the final digestion of the starch) will also develop symptoms to a lesser degree.  After the total elimination of  sucrose from the diet some children are able to tolerate normal portions of starch which on occasion may result in gassiness or diarrhea if eaten in a large quantity or without other food groups (mutation B).  The research suggests that children over three tolerated starch better than children under three (mutation B only).

The onset of symptoms can vary from just a few hours, in the worst cases, to 120 days, depending on the amount of sucrose and certain starches ingested and the period over which they were ingested.   Refer to the  compiled list of symptoms.

CSID is a commonly misdiagnosed genetic disorder, cases usually range from 1 month to an 18 month interval between the onset of symptoms and a correct diagnosis.  Some cases have gone as long as nineteen  years before being correctly diagnosed.

Common misdiagnoses are: cow's milk protein intolerance, colitis, irritable bowel syndrome, children's diarrhea, influenza,  fructose intolerance, food allergies, and inflammation of the pyloric sphincter.

The research literature suggests that determination of stool pH may be a clue to diagnosis.  It also indicates that about 1/3 of all CSID patients had a false negative hydrogen breath test for sucrose. It further indicates that disaccharidase determination is the key to a proper diagnosis of CSID.  This is done by taking a small-bowel biopsy (a tissue sample) from various points within the duodenum (area just beyond the exit point of the stomach) and the proximal jejunum (upper portion of the small intestine) to determine the levels of existing enzymes present. Dr. William Treem has written a number of articles regarding this test, the procedure, and interpretation of the results, which may be helpful for primary care physicians (please refer to list of citations in the research portion of this website.) 

There is currently no cure for CSID, but there are two treatments approved by the FDA that improve the quality of life.  One treatment is removing sucrose permanently and completely from the diet, and limiting starches high in amylopectin.   The other is utilizing Sucraid ™,  an artificial enzyme recently approved by the Food and Drug Administration which appears to allow children to ingest limited amounts of sucrose.  Sucraid was developed after research showed that lyophilized baker's yeast (saccharomyces cerevisiae) lessened the CSID symptoms of diarrhea and cramps.  A liquid yeast sucrase was developed and used in clinical studies and ultimately approved by the FDA for patient use. Other treatments and medications are under study and development at this time. A number of our members are participating in clinical studies ongoing at this time. We will post the results of these studies when completed.