Congenital enzyme defect resulting in chronic
diarrhea, dehydration, and failure to thrive.
Congenital Lactase Deficiency; Disaccharidase Deficiency
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
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
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
Semenza G, Auricchio S, Mantei N: Small-intestinal disaccharidases, in
Scriver CR, Beaudet AL, Sly WS, et al. (eds): The Metabolic ...