Studies of a Patient with Megaloblastic Anemia and an Abnormal Transcobalamin II

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Abstract
TRANSCOBALAMIN II, a 38,000-dalton plasma protein, has a single binding site for cobalamin (vitamin B12) and functions as the major protein for transporting cobalamin to various tissues.1 2 3 4 Table 1 lists the characteristics of four cases of hereditary absence of transcobalamin II as previously described.5 6 7 These characteristics suggested simple cobalamin deficiency, but since about 70 to 90 per cent of the endogenous cobalamin in serum is found on cobalamin-binding proteins known as R proteins, 1 and only 10 to 30 per cent of serum cobalamin is bound to transcobalamin II, the serum cobalamin levels were all considered normal. All the patients had . . .