Carbohydrate intolerance is a rare but very serious hereditary disorder. Cases due to lack of digestive enzyme and to impaired hexose transport have been reported. It is estimated that glucose-galactose malabsorption accounts for 2% of the patients with protracted diarrhea of infancy. In two reported cases of glucose-galactose malabsorption, the infants developed diarrhea soon after birth. Their stools contained reducing sugars and had an acidic pH. Analysis of tissue obtained by biopsy of the small intestine showed normal villi with normal disaccharidase values. Monosaccharide feeding (loading) tests showed a normal rise in blood glucose following a fructose load dose, which was tolerated well. This result was in contrast to a flat glucose curve in response to a glucose load, which was accompanied by marked abdominal distension, profuse diarrhea, and the presence of reducing sugars in the stools.
What is a reducing sugar? Why would it be increased in these patients?
Which monosaccharide transport protein is lacking in these patients? Give a rationale for your answer.
If the plasma glucose concentration had been monitored in these two patients following a load of sucrose, would a rise in plasma glucose have been observed? Give a rationale for your answer.
In terms of plasma glucose concentration, what would have been observed following a loading dose of lactose?
What would be an appropriate dietary treatment for these individuals?
Carbohydrate intolerance is a rare but very serious hereditary disorder. Cases due to lack of digestive enzyme and to impaired hexose transport have been reported. It is estimated that glucose-galactose malabsorption accounts for 2% of the patients with protracted diarrhea of infancy. In two reported cases of glucose-galactose malabsorption, the infants developed diarrhea soon after birth. Their stools contained reducing sugars and had an acidic pH. Analysis of tissue obtained by biopsy of the small intestine showed normal villi with normal disaccharidase values. Monosaccharide feeding (loading) tests showed a normal rise in blood glucose following a fructose load dose, which was tolerated well. This result was in contrast to a flat glucose curve in response to a glucose load, which was accompanied by marked abdominal distension, profuse diarrhea, and the presence of reducing sugars in the stools.
What is a reducing sugar? Why would it be increased in these patients?
Which monosaccharide transport protein is lacking in these patients? Give a rationale for your answer.
If the plasma glucose concentration had been monitored in these two patients following a load of sucrose, would a rise in plasma glucose have been observed? Give a rationale for your answer.
In terms of plasma glucose concentration, what would have been observed following a loading dose of lactose?
What would be an appropriate dietary treatment for these individuals?
