What Are the Symptoms of CSID?

In general terms, when individuals with Congenital Sucrase-Isomaltase Deficiency (CSID) eat food containing sucrose, they are unable to digest the sucrose and they develop gastrointestinal symptoms. Most of those with CSID have very little or absent sucrase activity, which is the enzyme needed for sucrose digestion. They also have varying levels of activity of the enzymes required for starch digestion (for example, isomaltase [palatinase] and maltase), so they may also experience gastrointestinal symptoms from consuming foods containing starch.

Gastrointestinal symptoms for those with CSID can vary from mild to severe. These symptoms occur because dietary sucrose moves through the small intestine undigested. The undigested sugar enters the colon, which causes diarrhea; and the normal bacteria present in the intestine digest the sugar by fermentation, which results in gas production. Diarrhea occurs when substances are not absorbed in the colon and retain water. This is referred to as osmotic diarrhea. Presenting symptoms may differ among infants, children, and adults.



Infants and Children

Infants do not manifest symptoms of CSID until they begin to ingest sucrose- and starch-containing foods (for example, fruit juices, solid foods, formula, and medications sweetened with sucrose). Infants who are exclusively breastfed may not show symptoms until the introduction of solid foods or until weaning. Common symptoms are chronic, watery diarrhea with or without failure to thrive (poor physical growth) and abdominal pain.

Infants may also present with abdominal swelling (distension), gassiness, colic, irritability, excoriated (abrasions and irritations) buttocks, diaper rash, and vomiting. A minority of infants may require hospitalization due to dehydration, malnutrition, muscle wasting, and weakness. Because children have shorter gastrointestinal tracts, their symptoms may be more severe than adults.

Some children with CSID are not diagnosed as infants and are presumed to have chronic, nonspecific diarrhea (toddler’s diarrhea). In older children, symptoms include abdominal pain, cramps, gas, and intermittent diarrhea. They may be incorrectly diagnosed with irritable bowel syndrome (IBS). In these children, a prolonged period of misdiagnoses may occur as individuals learn to live with their symptoms. The potential reasons for a delay in the diagnosis of CSID could be mistaken diagnoses of milk protein intolerance, food allergies, and chronic, nonspecific diarrhea. CSID is a genetic disease that individuals will not outgrow.




Adult symptoms are similar to those of infants and children but may be less severe due to the adult’s longer gastrointestinal tract. In adults, a prolonged period of misdiagnoses may occur as the adult learns to live with their uncomfortable gastrointestinal symptoms, or assumes their ongoing gastrointestinal problems to be normal. Recurrent symptoms similar to those caused by CSID, such as frequent bowel movements, chronic diarrhea, unexplained abdominal pain, gassiness, bloating, weight loss, abdominal distention, and vomiting should not be ignored.

In some adults, symptoms may be limited to an increase in bowel movement frequency, abdominal distention, and flatulence, with the occurrence of episodic watery diarrhea when eating foods containing a high concentration of sucrose. In some adults, diarrhea may alternate with constipation, leading to a misdiagnosis of irritable bowel syndrome (IBS). Consultation with a gastroenterologist is recommended to discuss any recurring, persistent gastrointestinal symptoms.

Failure to absorb dietary sucrose and starch may impact the absorption of other nutrients as well as the hormonal regulation of gastrointestinal function. Carbohydrates that have been consumed but not digested or absorbed accelerate the rate food moves from the small intestine to the large intestine (called transit time), a factor that contributes further to the malabsorption of dietary starch, fat, and monosaccharides. The severity of gastrointestinal symptoms is affected by several factors, including the quantity of sucrose or starch consumed, the level of bacterial activity present in the intestine, the absorptive capacity of the colon, the rate of gastric emptying, and small bowel transit time.



Gericke B, Amiri M, Naim HY. The multiple roles of sucrase-isomaltase in the intestinal physiology. Mol Cell Pediatr. 2016;3(1):2. doi.org/10.1186/s40348-016-0033-y