Congenital Sucrase-isomaltase Deficiency (CSID) is a chronic malabsorption disease characterised by an autosomal recessive inheritable disease of sucrase and isomaltase deficiency (Hauri, 1985; Kerry, 1965; Naim, 1988; Newton, 1996). Patients with CSID have a complete or almost complete lack of endogenous sucrase activity, a marked reduction in isomaltase activity, and a moderate decrease in maltase activity (Auricchio, 1965; Treem, 1993).
Sucrase is an enzyme produced in the brush border lining of the small intestine and is responsible for the metabolism of sucrose, a disaccharide commonly known as table sugar, into two component monosaccharides, glucose and fructose, which are then absorbed into the circulation (Sterchi, 1990; Treem, 1995).
In the absence of the sucrase enzyme, sucrose cannot be absorbed and passes unchanged into the large intestine.
The presence of intact disaccharides in the intestinal lumen leads to osmotic retention of water, resulting in loose stools (Treem, 1995). Unabsorbed sucrose in the large intestine is broken down by colonic bacteria, producing among other things the gases Hydrogen, methane, and carbon dioxide. These gases generate gastrointestinal discomfort including excessive gas, bloating, abdominal pain and cramps, watery diarrhea, nausea and vomiting (Berkow, 1992; Davidson, 1967).
Thus, children born with CSID develop a malabsorption syndrome upon first exposure to sucrose in their diet. Usually this is in the form of infant formula since breast milk does not contain sucrose. Because these children are unable to digest a significant portion of their caloric intake, they often have retarded growth and a failure to thrive (Antonowicz, 1972; Gudman-Hoyer, 1985; Newton, 1996; Treem, 1995). Added features may include irritability, lethargy and sleep disturbances.
CSID is a difficult disease to diagnose.