Transcobalamin II, Macrocytic Anemia (TCN2)

TCN2 encodes a member of the vitamin B12-binding protein family. This family of proteins, alternatively referred to as R binders, is expressed in various tissues and secretions. This plasma protein binds cobalamin and mediates the transport of cobalamin into cells. This protein and other mammalian cobalamin-binding proteins, such as transcobalamin I and gastric intrisic factor, may have evolved by duplication of a common ancestral gene.

Deficiency in TC II was demonstrated. A partial deficiency in both parents and other hematologically normal relatives indicated autosomal recessive inheritance. Decreased intestinal absorption of B12, uncorrected by intrinsic factor, suggested that transcobalamin II is involved in B12 absorption.