Vitamin B12 Deficiency



FUT and Vitamin B12 Deficiency


Fucosyltransferase codes for a gene responsible for the addition of fucose-sugars to terminal galactose molecules on proteins. In the absence of fucosylation, these terminal galactose residues are modified with sialic acid. Such heavily sialated proteins have been shown to have a longer half life in serum, and have been shown not to be removed as efficiently from serum as those with terminal fucose or galactose. The protein that normally removes these asialated proteins is the specific transport protein, the asialoglycoprotein receptor that recognizes terminal galactose or fucose and so removes the protein from serum. It is speculated that this way be a way of removing old or damaged proteins from serum. Studies have shown that haptocorrin, but not transcobalamin is glycosylated and the extent of fucosylation of haptocorrin is dependent upon the FUT2 genotype, with rs601388 genotype influencing the glycosylation of haptocorrin. The potential consequence of extra fucosylation is that a greater percentage of vitamin B12 circulating in serum would be bound by non-fucosylated, but sialated-haptocorrin, when compared to individuals possessing the fucosylated and non-sialated variants of haptocorrin. This would explain the lower apparent levels of vitamin B12 seen in these individuals. It would not though mean that there is a difference between the amount of vitamin B12 bound to the transport protein, transcobalamin (Velkova et at, 2017). Three variants of the FUT2 genotypes appear to be linked rs602662 (A>G), rs492602(G>A), and rs601338(G>A) and have each been shown to result in higher circulating levels of serum total B12, but not higher serum transcobalamin-bound B12. Two other less frequently typed FUT2 variants are rs1047781(A>T) and rs492602(A>G), which have also been shown to affect total B12 levels in serum, but not transcobalamin-bound B12 (Velkova etal 2017). The variation though in the serum levels of vitamin B12 are generally around 10-20%, however, the ability to determine if the B12 is an active or inactive analogue does is not distinguished by knowing FUT status. Further it is only those that are FUT2+/+ that are effected, which is around 25% of the population.


FUT vitamin B12 deficiency References

Velkova etal The FUT2 secretor variant pTrp154Ter influences serum vitamin B12 concentration via holohaptocorrin, but not holotranscobalami, and is associated with haptocorrin glycosylation. Hum Mol Genet 2017 26: 4974-4988


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The statements on this site compose a compendium of generally recognized signs of vitamin B12 deficiency, and problems that can then ensue They also are formulated from a summary of relevant scientific publications. In addition they may contain some forward looking statements of a general nature.
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