Transcobalamin II deficiency presenting with methylmalonic aciduria and homocystinuria and abnormal absorption of cobalamin.
Barshop BA, Wolff J, Nyhan WL, Yu A, Prodanos C, Jones G, Sweetman L, Leslie J, Holm J, Green R, et al.
Department of Pediatrics, University of California San Diego, La Jolla 92093.

An infant with deficiency of transcobalamin II (TCII) presented with virtually complete failure to thrive and life-threatening pancytopenia. Methylmalonic acid and homocystine were found in the urine. The concentration of B12 in the serum was 26 pg/ml. Fibroblasts derived from the patient failed to take up labeled cobalamin in the absence of a source of TCII. Uptake was normal in the presence of TCII. Treatment with parenteral cobalamin reversed the clinical and hematological manifestations of the disease but she developed glossitis when the interval between injections was lengthened. Intestinal absorption of 57Co-cobalamin was less than 1% and remained abnormal when highly purified human intrinsic factor was given along with the labeled B12. Absorption improved when the labeled B12 was given together with rabbit TCII. The data suggest that TCII as well as intrinsic factor is required for transport of cobalamin from the intestine to the blood.

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