In addition, it can reduce nutrient transport into a cell as happens with TCN (transcobalamin
carrier protein), which decreases vitamin B12 entry into the cell.
This discrepancy occurs because much of the vitamin B12 that is measured in the assay is bound to haptocorrin, whereas the functional vitamin B12 which is bound to transcobalamin
contributes much less to the assay of total B12.
Homocysteine and transcobalamin
and the risk of dementia and Alzheimer's disease: a prospective study.
Polymorphism C776G in the transcobalamin
II gene and homocysteine, folate and vitamin B12 concentrations.
Simultaneous increases in both MMA and total Hcy (tHcy) are seen in inherited intracellular cobalamin defects, vitamin [B.sub.12] deficiency, Imerslund-Grasbeck syndrome, and transcobalamin
Similarly, studies have also shown an increase in the transporter protein transcobalamin
in acute and chronic inflammatory states .
Metz, "A comparison of serum transcobalamin
levels in white and black subjects," The American Journal of Clinical Nutrition, vol.
The most common causes of vitamin B12 deficiency are gastritis, pernicious anemia, impaired gastric surgery, inflammatory bowel disease, pancreatic insufficiency, medications (proton pump inhibitors, colchicine, neomycin, H2-receptor antagonists, metformin, cholestyramine, anticonvulsants), inadequate intake (vegetarian diet) and nitric oxide exposure or genetic disorders like transcobalamin
Megalin is an endocytic receptor with a high affinity for the Cbl transport protein transcobalamin
II that can mediate Cbl cellular uptake through endocytosis of the transcobalamin
II-Cbl complex .
haemolysis.18 Vitamin B12 levels may be reported as normal or elevated in myeloproliferative disorders liver disease congenital transcobalamin
II deficiency intestinal bacterial overgrowth and antecedent administration of vitamin B12.18
Methionine synthase (MTR), methionine synthase reductase (MTRR), transcobalamin
2 (TC2), cystathionine beta synthase (CBS), and methylenetetrahydrofolate dehydrogenase (MTHFD1) are very important enzymes involved in folate/homocysteine (Hcy) metabolism and play essential roles in synthesis and repair of DNA and methylation reactions .
TCN2 encodes for transcobalamin
II which binds and transports vitamin B12 into the cell (Regec et al.