Congenital Sucrase-Isomaltase Deficiency




Congenital sucrase-isomaltase deficiency (CSID) is a genetic condition that affects a person's ability to digest certain sugars. People with this condition cannot break down the sugars sucrose (a sugar found in fruits, and also known as table sugar) and maltose (the sugar found in grains). CSID usually becomes apparent after an infant begins to consume fruits, juices, and grains. After ingestion of sucrose or maltose, an affected child will typically experience stomach cramps, bloating, excess gas production, and diarrhea. These digestive problems can lead to failure to thrive and malnutrition. Most affected children are better able to tolerate sucrose and maltose as they get older. CSID is inherited in an autosomal recessive pattern and is caused by mutations in the SI gene.


The symptoms of CSID only occur when sucrose and/or maltose are ingested. Symptoms may include:

  • chronic watery and or acidic diarrhea
  • colitis like symptoms
  • failure to thrive
  • weight loss
  • vomiting (in more severe cases-may be related to gene configuration)
  • abdominal distension
  • irritable bowel syndrome
  • abdominal pain
  • bloating
  • gassiness
  • colic or irritability
  • excoriated buttocks
  • severe diaper rash or appearance of slight burn from stomach acid
  • foul smelling fermented semi solid bowel movements
  • dehydration
  • malnutrition
  • slowed growth
  • slight yellowing of the skin (due to rising carotene levels in the blood)
  • inflammation of pyloric sphincter muscle between stomach and superior duodenum
  • Possible association with renal calculi (oxalate)
  • Possible copper malabsorption

Severity of symptoms are dependent on the quantity of sugar consumed as well as the colonic bacterial metabolic activity, absorptive capacity of the colon, rate of gastric emptying and small bowel transit time. Breast fed babies or infants consuming lactose-containing formulas will not manifest symptoms until sucrose is introduced into the diet in the form of fruit juices, solid foods and some medications. In young infants, passage of carbohydrate content through the small intestine and colon is typically more rapid than in adults, thus leading to more severe symptoms. In addition, because of the acceleration of transit (diarrhoea), the absorption of fats and starch is decreased, meaning that children with CSID sometimes have growth retardation. Intolerance to sucrose usually improves with age and symptoms of starch tolerance often disappear within the first few years of life. Although the symptoms appear to be less severe in adults, CSID is not a disease that a patient grows out of. The enzyme deficiency does not change with age but patients just become more tolerant. 


CSID is caused by a mutation in the 3rd chromosome along with a corresponding mutation in the 7th chromosome. The 3rd chromosome is related to the sucrase deficiency, while the 7th chromosome is related to the maltose deficiency, however the 7th chromosome does not have to be mutated for the diagnosis to occur. There are 5 different levels of CSID. Group C CSID patients do not have a mutation of the 7th chromosome, so they can have normal levels of starch. Groups A, B, D, and E however do have a mutation of the 7th chromosome, and depending on the severity of the mutation, may also be incapable of producing the common enzyme for breaking down milk sugar, lactase.

Group A (37%):

The people in this group cannot digest the sucrase or starch with out getting any of the symptoms, especially those relating to acid and gas. The person diagnosed can usually take Sucraid to assist with the digestion of natural sugars, such as those found in fruits and vegetables. Without the aid of Sucraid, the person cannot have any sugar and starch, excluding carbohydrates, in their diet. The amount of Sucraid need for a patient depends on the patient and the amount of food the patient eat.

Group B (42%):

The people in this group cannot have any sucrose without getting any symptoms, however, they can digest small amounts of starch without getting symptomatic. This group can also be given Sucraid to assist with the digestion of naturally occuring sugars. Children over the age of two (2) usually would require a vitamine supplemation in replacement of the sugar that they cannot digest.

Group C (11%):

This group cannot digest any sucrose, however they can digest the normal amounts of starches (after the age of 3). The symptoms usually are the most present and severe for patients in this group. Small children, usually under the age of 2, can loose up to 20% of their body weight, within 4-72 hours, after sucrose is first introduced to the body. This group, just like group A and B can take Sucraid to help aid with the natural sugar digestion.

Group D (10%):

The persons diagnosed with this group are usually found in New Zealand or Australia and cannot intake any sugar, lactose or starch without getting the symptoms. This group cannot normally have the same diets as the people in groups A, B or C. This group, however, along with all the others, can be given Sucraid to assist with the digestion of naturally occuring sugars. Because the patient cannot intake any starch, ketosis and weight loss are big problems. Unless they are given lactase, from their physician, the patient cannot intake any lactose either.

Group E:

Siblings, parents and grandparents of a patient who are heterozygotes often seem to have some of the symptoms, usually having to do with waste (in childhood). When older, most relatives do not experience any symptoms, however, 17% suffer from some of the symptoms, usually from mild gas to sever bawel movements. Most siblings do not eat much sugar and usually get symptoms when too much starch is consumed in a day. When starch is lowered, and there is an almost complete lack of sugar in the diet, most parents and granparents reported a lack in symptoms.


Prevention is impossible due to CSID being a genetic disorder.


CSID can be diagnosed by taking a small sample of tissue (biopsy) from the small intestine for a specific test known as a disaccharidase assay. Other tests may include a sucrose hydrogen breath test in which an abnormally high level of hydrogen will be detected in the breath of an affected individual after sucrose ingestion. Genetic testing may be indicated in some cases.

Further diagnostic methods are the breath hydrogen test and the 13C-breath test.


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.

Source: CSID Parent Support Group


CSID is typically treated by modifying a person's diet to reduce the amount of sucrose. Because many foods contain sucrose and other complex sugars, it can be difficult to completely remove sucrase from the diet. Sacrosidase is an oral medication containing the enzyme that does not work properly in people with this condition. By taking this medication, those with CSID can eat sucrose-containing foods because this enzyme will break down sucrose. This medication must be taken with each meal or snack.

Approved treatments:
Sacrosidase (Sucraid) FDA-approved indication: Oral replacement therapy of the genetically determined sucrase deficiency, which is part of congenital sucrease-isomaltase deficiency.



Refer to Research Publications.