Malabsorption of dietary folate occurs in tropical sprue, in gluten-induced enteropathy in children and in adults, when it is associated with dermatitis herpetiformis. In the rare congenital syndrome of selective malabsorption of folate, there is an associated defect of folate transport into the cerebrospinal fluid, and these patients show megaloblastic anaemia, responding to physiological doses of folic acid given parenterally but not orally. These patients also show mental retardation, convulsions and other central nervous system abnormalities. Minor degrees of malabsorption may also occur following jejunal resection or partial gastrectomy, in Crohn's disease and in systemic infections but, in these conditions, if severe deficiency occurs, it is usually largely due to poor nutrition.
Malabsorption of folate has been described in patients receiving salazopyrine, cholestyramine and triamterene. It has also been associated with anticonvulsant drug therapy, alcohol abuse and folate deficiency, but these relationships are less well established. In the intestinal stagnant loop syndrome, the predominant effect of the small intestinal bacteria is to cause a rise in serum, red cell and urinary folate by synthesizing folate, which is then absorbed.
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