Dictionary of Human Evolution and Biology

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Glucose-galactose Malabsorption

A cell membrane transport defect characterized by severe diarrhea and dehydration in early infancy; fatal if lactose and sucrose sugars are not removed from the diet and replaced by a fructose-based formula. The defective gene is an autosomal dominant, solute carrier family 5, member 1 (SCC5A1, aka SGLT1), that normally transports glucose and galactose from the lumen of the small intestine into the intestinal cells. Mutations in SGLT1 reverse this process, and the unabsorbed sugars draw water from the intestinal cells, causing diarrhea. The double G-G form is rare, only 200 cases diagnosed annually worldwide, but less severe forms (glucose intolerance) affect 10% of the world’s population.

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