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The FUT2 secretor variant p.Trp154Ter influences serum vitamin B12 concentration via holo-haptocorrin, but not holo-transcobalamin, and is associated with haptocorrin glycosylation.

ABSTRACT: Vitamin B12 deficiency is common in older individuals. Circulating vitamin B12 concentration can be used to diagnose deficiency, but this test has substantial false positive and false negative rates. We conducted genome-wide association studies (GWAS) in which we resolved total serum vitamin B12 into the fractions bound to transcobalamin and haptocorrin: two carrier proteins with very different biological properties. We replicated reported associations between total circulating vitamin B12 concentrations and a common null variant in FUT2. This allele determines the secretor phenotype in which blood group antigens are found in non-blood body fluids. Vitamin B12 bound to haptocorrin (holoHC) remained highly associated with FUT2 rs601338 (p.Trp154Ter). Transcobalamin bound vitamin B12 (holoTC) was not influenced by this variant. HoloTC is the bioactive the form of the vitamin and is taken up by all tissues. In contrast, holoHC is only taken up by the liver. Using holoHC from individuals with known FUT2 genotypes, we demonstrated that FUT2 rs601338 genotype influences the glycosylation of haptocorrin. We then developed an experimental model demonstrating that holoHC is transported into cultured hepatic cells (HepG2) via the asialoglycoprotein receptor (ASGR). Our data challenge current published hypotheses on the influence of genetic variation on this clinically important measure and are consistent with a model in which FUT2 rs601338 influences holoHC by altering haptocorrin glycosylation, whereas B12 bound to non-glycosylated transcobalamin (i.e. holoTC) is not affected. Our findings explain some of the observed disparity between use of total B12 or holoTC as first-line clinical tests of vitamin B12 status.

SUBMITTER: Velkova A

PROVIDER: S-EPMC5886113 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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The FUT2 secretor variant p.Trp154Ter influences serum vitamin B12 concentration via holo-haptocorrin, but not holo-transcobalamin, and is associated with haptocorrin glycosylation.

Velkova Aneliya A Diaz Jennifer E L JEL Pangilinan Faith F Molloy Anne M AM Mills James L JL Shane Barry B Sanchez Erica E Cunningham Conal C McNulty Helene H Cropp Cheryl D CD Bailey-Wilson Joan E JE Wilson Alexander F AF Brody Lawrence C LC

Human molecular genetics 20171201 24

Vitamin B12 deficiency is common in older individuals. Circulating vitamin B12 concentration can be used to diagnose deficiency, but this test has substantial false positive and false negative rates. We conducted genome-wide association studies (GWAS) in which we resolved total serum vitamin B12 into the fractions bound to transcobalamin and haptocorrin: two carrier proteins with very different biological properties. We replicated reported associations between total circulating vitamin B12 conce ...[more]

PMID: 29040465

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Project description:Abstract Objectives Background: The FUT2 gene is responsible for the secretion of ABO blood type antigens into the body fluids (saliva, mucous, urine, tears, breast milk, sweat, and semen). Those who secrete the antigens into body fluids are call secretors, those who do not are called non-secretors. Hypothesis: GWAS studies have reported FUT gene variants to be associated with circulating vitamin-B12 (Vit-B12) concentrations. Missense mutations in the FUT2 gene result in a non-secretor phenotype. Thus, the secretory status of an individual may affect circulating vitamin-B12 concentrations over and above the genotype. Methods Materials and Methods: We included 780 participants (271 children, 282 mothers, and 227 fathers) from Pune Maternal Nutrition Study (PMNS). We measured the secretor status of individuals in saliva by hemagglutination test. A total of eight genetic variants including six SNPs from the FUT2 gene (rs492602, rs681343, rs281377, rs601338, rs1800027, and rs602662) and two SNPs from the FUT6 gene (rs3760776 and rs3760775) from our previous GWAS study were correlated with circulating vitamin-B12 levels. We tested the associations of FUT gene variants with secretor status phenotype and of the secretor phenotype with circulating vit-B12, folate, and ferritin concentrations in addition to H.pylori antibody levels. Results Results and Discussion: We found 33% of participants were non-secretors compared to 20% reported in Western Caucasian populations. Non-secretors had higher vitamin-B12 concentrations but not of folate and ferritin, vitamin-B12 associations were over and above FUT genotypes. Non-secretors showed a higher response to Vit-B12 supplementation. We found a FUT2 haplotype () to be strongly associated with Vit-B12 concentrations and non-secretor status. Non-secretors had lower H.pylori antibody concentrations. FUT6 genotype and haplotype were associated with Vit-B12 concentrations but not with secretor status and H.pylori antibody levels. Conclusions Our data suggest that secretor status may influence Vit-B12 concentrations through susceptibility to H.pylori infection and possibly other gut microbiota. A higher frequency of non-secretors in Indians could offer a selective advantage against Vit-B12 deficiency. Funding Sources BBSRC, UK; MRC, UK; WELLCOME TRUST, UK; DBT, India; ICMR India

Dataset Information

The FUT2 secretor variant p.Trp154Ter influences serum vitamin B12 concentration via holo-haptocorrin, but not holo-transcobalamin, and is associated with haptocorrin glycosylation.

Publications

The FUT2 secretor variant p.Trp154Ter influences serum vitamin B12 concentration via holo-haptocorrin, but not holo-transcobalamin, and is associated with haptocorrin glycosylation.

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