Congenital enzyme defect resulting in chronic diarrhea
and failure to thrive.
Congenital Sucrase-Isomaltase Deficiency; Disaccharidase
Deficiency Type I.
Varies with ethnic group (whites: 1:2500, native
Alaskans: 1:33, native Canadians: 4-7:100).
Autosomal recessive. The gene encoding for
sucrase-isomaltase deficiency is localized on the long arm of chromosome 3.
The absence or severe reduction in sucrase and
isomaltase activity in the brush-border membrane of the small intestine is
responsible for malabsorption of dietary disaccharides and starch. When
these carbohydrates are introduced into the diet, they generate an osmotic
pressure gradient in the intestinal lumen, attracting large volumes of
isotonic fluid with normal sodium concentration. The capacity for colonic
bacteria to ferment malabsorbed carbohydrates is rapidly overwhelmed, and
osmotic diarrhea ensues.
Starch is a mixture of the two polysaccharides
amylopectin and amylose. Hydrolysis of amylopectin and amylose yields mainly
maltose, maltotriose, and glucose. Clinical presentation, oral tolerance
test with the corresponding disaccharides, sucrose breath hydrogen test,
differential urinary disaccharide excretion, and measurement of intestinal
disaccharidase activity in a small intestine biopsy lead to the diagnosis.
Disaccharidase deficiency is defined as an enzyme activity of at least two
standard deviations below the normal mean value. A jejunal biopsy is the
gold standard for the diagnosis because the disaccharidase levels are
normally the highest here; however, the specimen is difficult to obtain.
Furthermore, the circadian rhythm of enzyme activity must be considered.
The clinical presentation varies and depends on
the introduction of sucrose and starch to the diet. Once the diet ceases to
consist exclusively of breast milk and lactose-free formulas, the
introduction of sucrose-containing juices, solid food, or even medications
causes chronic osmotic-fermentative diarrhea and, occasionally, failure to
thrive. Decreased duodenal-ileal transit time may compromise fat absorption.
Empiric avoidance of dietary sucrose load may delay the diagnosis up to the
toddler age (children show relatively normal growth but suffer from
intermittent diarrhea with meteorism and abdominal cramps). A minority of
patients requires hospitalization for severe dehydration, malnutrition, and
muscle wasting. Lifelong elimination of sucrose and reduction of starch
content in the diet leads to complete recovery.
Obtain a full history of
gastrointestinal symptoms (severity of diarrhea and degree of malnutrition)
causing failure to thrive. In rare cases, TPN is required. Evaluate volume
status clinically and check electrolytes, blood urea nitrogen, and
creatinine. If the patient is on TPN, also check serum concentrations of
albumin, glucose, phosphate, calcium, magnesium, transaminases, alkaline
phosphatase, and bilirubin. Optimize volume status preoperatively by
Consider repeated intraoperative blood
glucose monitoring if the patient is on TPN.
In the presence of severe
malnutrition (rare) or depressed renal and/or hepatic function secondary to
complications from TPN, highly protein-bound drugs must be titrated
carefully secondary to low protein levels (in particular α1-acid glycoprotein and albumin), which may result in decreased drug
binding and increased free drug levels.