Selective Malabsorption of Vitamin B12

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Abstract
A 9-year-old boy with selective malabsorption of vitamin B12had megaloblastic anemia, proteinuria, failure to absorb orally administered radioactive vitamin B12, low serum B12levels, increased excretion of methylmalonic acid (MMA), and absence of intrinsic factor antibodies. While the anemia and MMA excretion responded quickly to parenteral vitamin B12therapy, a generalized aminoaciduria persisted. Sufficient therapy was documented by inability to increase urinary MMA excretion with an oral dl-valine load. Elevated excretion or clearance of threonine, alanine, tyrosine, histidine, glycine, serine, and leucine was present before and after therapy supporting the concept of an associated distinct renal tubular defect separate from vitamin B12dependent metabolic pathways.

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