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Congenital enzyme defect resulting in chronic diarrhea, dehydration, and failure to thrive.

Congenital Lactase Deficiency; Disaccharidase Deficiency Type II.

Genetic disorder manifested by chronic diarrhea.

Fewer than 100 cases have been reported worldwide, with the majority in Finland.

Autosomal recessive. The congenital lactase deficiency gene is localized on the long arm of chromosome 2.

Lactose, the main carbohydrate in milk and dairy products, is a disaccharide composed of glucose and galactose. In congenital lactase deficiency, the enzyme is present only at trace levels in the small intestine brush-border membrane. As a consequence of lactase deficiency, high concentrations of unabsorbed lactose remain in the intestinal lumen and generate an osmotic diarrhea.

Clinical presentation, a trial of lactose-free diet, breath hydrogen test, and assay of lactase activity in a jejunal biopsy specimen.

Onset is very early in life (in the first hours or days of life), with watery diarrhea upon introduction of lactose-containing milks. Diarrhea is severe and results in rapid dehydration, malnutrition, failure to thrive, and high lactose concentration in the feces. Total remission with normal growth and psychomotor development occurs with a lactose-free diet.

Evaluate volume status clinically and check serum electrolytes, blood urea nitrogen, and creatinine. Pay special attention to renal function and serum calcium levels because hypercalcemia and nephrocalcinosis have been described. Delay elective surgery until the patient is well rehydrated and acid-base status is corrected. If the patient is on TPN, also obtain serum concentrations of albumin, glucose, phosphate, magnesium, transaminases, alkaline phosphatase, and bilirubin. Optimize volume status preoperatively by intravenous rehydration.

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 have to be titrated carefully, secondary to low protein levels (particularly α1-acid glycoprotein and albumin), which may result in decreased drug binding and increased free drug levels.

Disaccharide Intolerance Type I: Congenital enzyme defect resulting in chronic diarrhea and failure to thrive.

Severe Infantile Lactose Intolerance: On a lactate-containing diet, affected children become severely ill and present with vomiting, acidosis, lactosuria, aminoaciduria, and failure to thrive. Cataract occurs occasionally. The cause of this disorder has not been fully elucidated, but it seems that jejunal lactase activity is normal and that the defect is caused by an abnormal permeability of the intestinal mucosa.

Jarvela I, Sabri Enattah N, Kokkonen J, et al: Assignment of the locus for congenital lactase deficiency to 2q21, in the vicinity of but separate from the lactase-phlorizin hydrolase gene. Am J Hum Genet 63:1078, 1998.  [PubMed: 9758622]
Semenza G, Auricchio S, Mantei N: Small-intestinal disaccharidases, in Scriver CR, Beaudet AL, Sly WS, et al. (eds): The Metabolic ...

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