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Common variants of FUT2 are associated with plasma vitamin B12 levels

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We identified a strong association (P = 5.36 x 10(-17)) between rs492602 in FUT2 and plasma vitamin B(12) levels in a genome-wide scan (n = 1,658) and an independent replication sample (n = 1,059) from the Nurses' Health Study. Women homozygous for the rs492602[G] allele had higher B(12) levels. This allele is in strong linkage disequilibrium with the FUT2 nonsecretor variant encoding W143X, suggesting a plausible mechanism for altered B(12) absorption and plasma levels.
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Common variants of FUT2 are associated with plasma vitamin
B12 levels
Aditi Hazra1,2, Peter Kraft1, Jacob Selhub3, Edward L. Giovannucci2,4, Gilles Thomas5,
Robert N. Hoover5, Stephen J. Chanock5, and David J. Hunter1,2,4,5
1Program in Molecular and Genetic Epidemiology, Department of Epidemiology, Harvard School of Public
Health, 677 Huntington Avenue, Boston, MA 02115, USA.
2Channing Laboratory, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical
School, 181 Longwood Avenue, Boston, MA 02115, USA.
3Vitamin Metabolism and Aging Laboratory, Jean Mayer US Department of Agriculture Human Nutrition
Research Center on Aging, Tufts University, Boston, MA 02111, USA.
4Department of Nutrition, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115,
USA.
5Division of Cancer Epidemiology and Genetics, National Cancer Institute(NCI), US National Institutes of
Health (NIH), Department of Health and Human Services (DHHS), Bethesda, Maryland 20892, USA.
Abstract
We identified a strong association (p=5.36×1017) between rs492602 in FUT2 and plasma vitamin
B12 levels in a genome-wide scan (n=1,658) and an independent replication sample (n=1,059) from
the Nurses' Health Study. Women homozygous for the rs492602 G allele had higher B12 levels. This
allele is in strong linkage disequilibrium with the FUT2 W143X nonsecretor variant, suggesting a
plausible mechanism for altered B12 absorption and plasma levels.
Keywords
one-carbon metabolism; plasma vitamin B12; genome-wide association; FUT2; secretor locus
Plasma levels of vitamin B12 are modifiable quantitative traits associated with certain
diseases1. Vitamin B12 found in meat (such as liver, shellfish, fish, poultry, and eggs) and milk
products2 is composed of corrin and cobalt rings and is necessary for the formation of red
blood cells, DNA synthesis during cell division, and maintenance of the myelin nerve sheath.
Deficiency in vitamin B12, clinically associated with pernicious anemia, cardiovascular
disease, cancer, and neurodegenerative disorders, is often related to poor intestinal B12
absorption2 rather than direct dietary deficiency (the recommended adult intake for vitamin
B12 is 2.4 µg/day). In the Nurses’ Health Study (NHS), we previously observed that women
in the lowest quartile of plasma vitamin B12 levels had marginally worse cognitive performance
(based on a global score averaging 6 cognitive tests) than women in the highest quartile of
plasma vitamin B12 and that combined folate and vitamin B12 deficiency was associated with
the lowest cognitive performance3.
To whom correspondence should be addressed: David J. Hunter, Department of Epidemiology, Harvard School of Public Health, 677
Huntington Ave, Boston, MA 02115, Phone: 617-525-2755; Fax: 617-525-2008, Email: E-mail: dhunter@hsph.harvard.edu.
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Published in final edited form as:
Nat Genet. 2008 October ; 40(10): 1160–1162. doi:10.1038/ng.210.
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Epidemiologic studies provide evidence for the association of genes and metabolites in the B-
vitamin-mediated plasma one-carbon metabolic pathway with chronic diseases2–4. Rare high
penetrance mutations in genes in this pathway affect the ability to digest, absorb5, and utilize
vitamin B122. However, common genetic variants in candidate genes have not been
consistently associated with plasma vitamin B12 levels. Therefore, we conducted a genome-
wide association study (GWAS) to identify novel loci that influence plasma vitamin B12 levels
in 1,658 women genotyped with the HumanHap500 as part of the Cancer Genetic Markers of
Susceptibility Project (CGEMS; Supplementary Methods). Participants were of self-reported
European ancestry6. Detailed methods have been previously reported, including quality control
assessment of genotypes with sample completion and SNP call rates, concordance rate,
deviation from Hardy–Weinberg proportions in control DNA, and final sample selection for
association analysis of the NHS CGEMS population6.
We tested association between each of the 528,134 SNP markers that passed quality control
filters and log-transformed plasma vitamin B12 using linear regression, adjusted for age, total
methyl intake (defined as total folate, dietary methionine, and alcohol intake), and assay batch.
We saw no evidence for systematic bias in the distribution of p-values for analyses with and
without further adjustment for residual population structure using the top four principal
components of genetic variation (Supplementary Fig. 1), compatible with no confounding of
SNP-metabolite associations due to population stratification.
In the initial GWAS, the SNPs on chromosome 19p13.3 accounted for the excess of p-values
<107 (Supplementary Fig. 1: Quantile-Quantile plot). The strongest association with plasma
vitamin B12 was rs602662 (Ptrend = 6.54×1010; Fig. 1, Table 1, Supplementary Fig. 2), a non-
synonymous SNP in FUT2 on chromosome 19p13.3, which has a minor allele frequency of
0.49 (Table 1). The association with plasma vitamin B12 and rs602662 was independently
replicated using Taqman allelic discrimination assays in 1,059 women from two nested case
control studies drawn from the same cohort (Table 1, Supplementary Table 2) with ptrend=1.13
× 10 06. The joint analysis of the CGEMS scan data and the replication dataset supports the
association of rs602662 with plasma vitamin B12 (ptrend = 3.51×1015). Results were similar
using untransformed plasma vitamin B12 values. A similar association was observed using the
non-parametric Kruskal-Wallis test (joint analysis Kruskal-Wallis p = 1.48×1021). Plasma
vitamin B12 has an inverse correlation in this data set with plasma homocysteine, an integrated
marker of the one-carbon metabolism pathway, (Spearman correlation coefficient 0.26,
p<0.0001). FUT2 rs602662 also has a modest association with plasma homocysteine,
(ptrend=0.0085 in the GWAS data and ptrend=0.0081 in the replication data). The pattern of
mean log-transformed plasma vitamin B12 levels by rs602662 genotype suggest a dominant
genetic effect, with lower B12 levels among variant carriers (test comparing mean log-
transformed vitamin B12 levels between variant carriers and non-carriers p = 1.35 × 1039).
The SNP rs602662 is in strong linkage disequilibrium (D’=1, r2=0.76) with the FUT2 nonsense
SNP W143X (rs601338; Fig. 1). We imputed the nonsense SNP in the initial GWAS samples
using the observed chromosome 19 genotyping data augmented by data from the densely-
genotyped CEPH European HapMap samples and found that it was strongly associated with
plasma vitamin B12 levels (ptrend=4.11×1010; Fig. 1, Table 1). Since the nonsense SNP
rs601338 could not be genotyped by Taqman because of a neighboring SNP (rs1800459)
located one nucleotide upstream, we genotyped a proxy SNP, rs492602 (which is in perfect
LD with rs601338 in HapMap data; Supplementary Table 1, Supplementary Fig. 3), in both
the initial GWAS and the replication data set. The association between rs492602 and plasma
vitamin B12 was stronger than the association for rs602662 and plasma vitamin B12 (Table 1:
rs492602 joint ptrend=5.36×1017; joint dominant model p =8.26×1045). The rs492602 SNP
explains 2.5% of the variance in log-transformed plasma vitamin B12 levels using the log-
additive genetic model and 3.5% of variance using the dominant genetic model.
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Fucosylated carbohydrate structures are involved in a range of biological processes7,8
including tissue development, angiogenesis, fertilization, cell adhesion, inflammation, and
tumor metastasis. The classic human secretor locus (Se) FUT2 encodes α(1,2)
fucosyltransferase, which regulates expression of the Lewis ABO(H) histo-blood group
antigens on the surface of epithelial cells and in body fluids and determines the secretion status
of the ABO antigens7. Secretor status of this polymorphic protein was used by Mohr to provide
the first autosomal linkage in humans between secretor factor and the Lutheran blood group;
subsequently secretor linkage was established with the APOE and myotonic dystrophy
locus7. The family of α-1,2-fucosyltransferases catalyze the addition of fucose in α-1,2-linkage
to the galactose of type 1(Galβ1,3GlcNAc-R) and type 2 Galβ1,4GlcNAc- R) disaccharide to
form H type 1 and H type 2 antigens7, respectively.
In the highly polymorphic FUT2 gene7, three SNPs, rs602662, rs492602 and rs601338
(W143X; nucleotide position 428), are in strong LD, we note that W143X is a nonsense
mutation7 and is plausibly the causal variant for the association with plasma B12 levels. The
143X variant is characteristic for the nonsecretor allele in Europeans and has an allele frequency
of 0.46 in populations of European ancestry7. In Europeans, Africans, and Iranians, the FUT2
W143X nonsense mutation is the primary nonsecretor allele, with a frequency of approximately
50 percent. In contrast, in Asian populations, the FUT2 I129F (nucleotide position 385)
missense mutation is the primary nonsecretor allele8. In non-Asian populations, nonsecretors
are frequently homozygous for the FUT2 W143X polymorphism, resulting in an inactive
FUT2. Individuals homozygous for the FUT2 nonsecretor genotype appear to be resistant to
infection with Norovirus9, suggesting that individuals homozygous for nonsecretor status may
be unable to mediate host-microbe interactions9.
Absorption of B12 requires the secretion of the glycoprotein intrinsic factor (IF) from the gastric
cells, binding of IF to vitamin B12 and a functional gastrointestinal absorption system2. The
H-antigen synthesized by FUT2, Lewis ABO antigens, and FUT2 genotypes have all been
reported to mediate H. pylori attachment to human gastric mucosa10. Atrophic gastritis is a
consequence of H. pylori infection11 and leads to reduced secretion of IF12,14. The FUT2
secretor status has been associated with both H. pylori infection and gastritis10; patients with
vitamin B12 malabsorption and low levels of serum vitamin B12 have higher seroprevalence
of H. pylori infection10. These data suggest a potential mechanism by which vitamin B12
absorption12–15 may be reduced in carriers of the secretor genotype due to the sequelae of
susceptibility to H. pylori infection compared to individuals with the nonsecretor genotype.
In summary, among generally well-nourished women, we found that common variation in the
FUT2 secretor gene is associated with plasma vitamin B12 at high levels of statistical
confidence. Although the participants included in these analyses are a selected subset of women
who had plasma vitamin B12 levels measured, numerous demographic and lifestyle factors are
comparable between this sample and the overall NHS cohort. Insights gained from the study
of plasma vitamin B12 are likely to have implications for the study of complex diseases such
as cognitive decline, cancer, and cardiovascular disease. Further study is required to investigate
the biological basis of our reported association findings.
The commonly used abbreviations are
FUT2, Fucosyltransferase; GWAS, genome-wide association study; H. pylori, Helicobacter
pylori; NHS, Nurses’ Health Study; CI, confidence interval; SNPs, single nucleotide
polymorphisms.
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Acknowledgements
We thank Hardeep Ranu, Constance Chen, and the staff at the Core Genotyping Facility at the National Cancer Institute
for their expertise.
This research is supported by the National Institutes of Health Research Grants U54 CA100971, P01 CA87969, P01
CA55075, U01 CA098233, R01 CA 065725 and CA070817.
A.H. is supported in part by training grant NIH T-32 CA 09001-30.
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Figure 1. LD Structure of Chromosome 19
This panel shows the trend P values for association testing with plasma vitamin B12 from 25
observed ( ) and 44 imputed ( ) SNPs from the GWA study displaying SNPs on chromosome
19p13.3. All known genes are shown (National Center for Biotechnology Information build
36.1)
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Table 1
Association of plasma vitamin B12 levels with FUT2 genotypes in women participants from GWAS and replication studies
SNP Association by
Study Age N Allele Freq Estimate (S.E.)cP-valued
Geometric Mean (95% CI), pg/ml
rs602662 GWAS G (Gly)=0.49 Ser/Ser Ser/Gly Gly/Gly
NHS CGEMS 59 1,658 489.82 418.67 417.05 0.08 (0.01) 6.54 × 1010
(472.24–508.06) (407.74–429.90) (401.29–433.43)
Replication
Combined NHS 63 1,056 483.68 406.96 409.60 0.08 (0.02) 1.13 × 1006
Colorectal (CR e)(461.78–506.63) (393.69–420.67) (390.22–429.93)
Adenoma and CR
Cancer
Case-control Datasets
TOTAL (GWAS and
Replication) e487.72 413.35 413.52 0.08 (0.01) 3.52 × 1015
(473.80–502.06) (404.83–422.06) (401.14–426.27)
rs601338b aA (Trp)=0.51 Nonsecretor Secretor Secretor
(X/X) (X/Trp) (Trp/Trp)
GWAS
NHS CGEMS 59 1,658 496.60 418.69 418.32 0.08 (0.01) 4.11 × 1010
(477.89–516.04) (407.76–429.92) (403.36–433.84)
rs492602 GWAS a A=0.51 GG/GG AG/AG AA/AA
NHS CGEMS 59 1,637 496.02 419.95 416.97 0.08 (0.01) 2.68 × 1010
(477.32–515.45) (408.88–431.31) (402.14–432.35)
Replication
Combined NHS CR 63 1,059 491.13 407.67 406.61 0.10 (0.02) 5.60 × 1009
Adenoma and CR
Cancer (469.03–514.26) (394.34–421.45) (389.46–424.53)
Case-control Datasets
TOTAL (GWAS and
Replication)f493.89 414.27 412.70 0.09 (0.01) 5.36 × 1017
(479.42–508.81) (405.69–423.04) (401.33–424.40)
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Hazra et al. Page 7
aMajor allele according to HapMap CEU data
bImputed distribution for nonsense polymorphism, rs601338 (also known as W143X)
cEstimates (regression coefficients) calculated from linear regression adjusted for age using log-transformed plasma vitamin B12 (same estimates obtained when adjusting for age, assay batch and total
dietary methyl status)
dP-values: GWAS and replication p-values are calculated from linear regression adjusted for age
ecolorectal is abbreviated as CR
fDominant model p-value for the joint analysis: rs602662 = 1.35 × 1039; rs492602= 8.26 × 1045
Nat Genet. Author manuscript; available in PMC 2009 April 27.
... Our PheWAS and Open Targets Genetics Portal analysis for this variant identified 141 associations spanning multiple disease areas, phenotypes and biomarkers ( Supplementary Tables 7 and 8). In summary, the allele associated with increased risk of chronic sputum production was associated with increased risk of gallstones [43,45,46], type 1 diabetes [47] and Crohn's disease [48][49][50][51], elevated vitamin B12 [52][53][54][55] and cholesterol and fat metabolites [42,43,[56][57][58][59][60], hypertension/cardiovascular disease [43,45,61], excess alcohol with associated sequelae [45,[62][63][64], increased risk of mumps and lower risk of childhood ear infections [65]. Higher risk of chronic sputum production was also associated with higher levels of gamma glutamyl transferase, total bilirubin and aspartate amino transferase, and lower levels of alanine aminotransferase and alkaline phosphatase. ...
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... Recent studies suggested that FUT2 polymorphism (secretor status) is associated with susceptibility to various infectious diseases, such as norovirus, rotavirus, COVID-19, and several clinical conditions such as Crohn's disease and low plasma vitamin B 12 levels [16][17][18][19] . Large scale replication studies of various populations or independent samples are important for con rmation of these associations. ...
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The se del allele is one of the nonsecretor alleles ( se ) of FUT2 generated by an Alu-mediated recombination event and was first found in an Indian Bombay phenotype. Like se del , se 302 having a missense single nucleotide polymorphism (SNP), 302C > T, is characteristic of South Asians with a frequency of 10–30%. We developed a real-time PCR melting curve analysis for detection of se del using a 127-bp amplicon encompassing the breakpoint junction. In addition, by performing duplex PCR by amplifying a 65-bp amplicon of the FUT2 coding region at the same time, we could determine the zygosity of se del in a single tube. We also developed an Eprobe-mediated PCR assay (Eprobe-PCR) for detection of 302C > T of FUT2. These methods were validated by analyzing 58 Tamils and 54 Sinhalese in Sri Lanka. Both the duplex PCR melting curve analysis for determination of se del zygosity and the Eprobe-PCR assay for detection of 302C > T exactly determined three genotypes. In addition, the results of the present methods were in complete agreement with those obtained by previously established methods. The two present methods were reliable and seem to be advantageous for large-scale association studies of FUT2 polymorphisms in South Asian populations.
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Background The ABO(H) secretor status is controlled by FUT2-encoded α(1,2)fucosyltransferase (Se enzyme) activity. Three SNPs of FUT2, 302C>T (rs200157007), 385A>T (rs1047781), and 428G>A (rs601338), cause three major variants of nonsecretor (se) or weak-secretor (Sew) alleles. Evidence has been accumulating that suggests the secretor status is associated with various conditions including infectious diseases but a robust multiplex method for assaying relatively large-scale samples to determine the genotype of these three SNPs simultaneously has not been developed yet. Methods By combined usage of two Eprobes and a dual-labeled fluorescence probe, we developed a real-time PCR, followed by triplex probe-based fluorescent melting-curve analysis (FMCA) for genotyping of 302C>T, 385A>T, and 428G>A of FUT2 in a single tube. Results Three genotypes of each of three variants of FUT2 were accurately determined by the triplex probe-based FMCA. We then validated this method using genomic DNA samples of 47 Bangladeshis, and the results obtained by using this method were fully concordant with those by previous Sanger sequencing. Conclusions Since the present single triplex probe-based FMCA is robust, fast, and cost-effective, we are able to effectively estimate the secretor status of subjects on a large scale in many populations around the world.
Article
Background: Fucosyltransferase 2 (FUT2) participates in intestinal antigen secretion and bacterial adherence. FUT2 homozygous nonsense mutations (FUT2M) and subsequent nonsecretor status is associated with Crohn's disease (CD). The common null allele is rs601338. We assessed the relationship between FUT2M and disease course. Methods: In consecutive adult CD outpatients, clinical, biochemical, and genetic data were collected at baseline visits. Patients were longitudinally followed over 5 years. The primary outcome analyzed the relationship between FUT2M and rates of CD patients in persistent steroid-free clinical remission requiring neither surgery, biologics, nor immunomodulators. Results: Sixty-two CD patients were recruited. FUT2M homozygotes (rs601338 or any mutation in linkage disequilibrium) were detected in 27% of CD (17/62). Patients with rs601338 mutations had higher rates of the primary outcome (homozygous: 46.6%, heterozygous: 28.0%, wild-type: 5.3%, P=0.02). Similar findings existed for CD patients with homozygous mutations in any single-nucleotide polymorphism for FUT2 (homozygous: 41.2%, heterozygous: 25.9%, wild-type: 5.6%, P=0.04). On multivariable analysis, rs601338 mutation was associated with the primary outcome (odds ratio=3.4, 95% confidence interval: 1.3-8.7, P=0.01), while other parameters were not. Mutation of rs601338 was associated with lower rates of penetrating disease (homozygous: 13.3%, heterozygous: 28.0%, wild-type: 52.6%, P=0.05) and particularly in high-risk patients (homozygous: 0%, heterozygous: 37.5%, wild-type: 83.3%, P=0.01). Conclusions: FUT2 mutation status is associated with a favorable clinical course in CD. Further confirmatory studies are needed.
Article
Introduction: We aimed to define the impact of the genetic background on overt hepatic encephalopathy (HE) in patients with liver cirrhosis by developing a combined clinical-genetic risk score. Methods: Patients suffering from liver cirrhosis from the outpatient clinics of 4 hospitals (n = 600) were included and followed up for at least 5 years until HE bouts, liver transplant, or death. Patients were genotyped for 60 candidate single nucleotide polymorphisms together with the microsatellite in the promoter region of the gene GLS. Results: Single nucleotide polymorphisms rs601338 (FUT2), rs5743836 (TRL9), rs2562582 (SLC1A3), rs313853 (SLC1A5), and GLS microsatellite did predict independently the incidence and severity of overt HE and were included as genetic score. Competing risk analysis revealed that bilirubin (subhazard ratio [sHR] 1.30 [1.15-1.48], P < 0.001), albumin (sHR 0.90 [0.86-0.93], P < 0.001), genetic score (sHR 1.90 [1.57-2.30], P < 0.001), and previous episodes of overt HE (sHR 2.60 [1.57-4.29], P < 0.001) were independently associated to HE bouts during the follow-up with an internal (C-index 0.83) and external validation (C-index 0.74). Patients in the low-risk group had 5% and 12% risk of HE at 1 (log-rank 92.1; P < 0.001) and 5 (log-rank 124.1; P < 0.001) years, respectively, whereas 36% and 48% in the high-risk group. Discussion: The genetic background influenced overt HE risk and severity. The clinical-genetic HE Risk score, which combined genetic background together with albumin, bilirubin, and previous episodes of overt HE, could be a useful tool to predict overt HE in patients with cirrhosis.
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Synthesis of soluble A, B, H, and Lewis b blood group antigens in humans is determined by the Secretor (Se) (FUT2) blood group locus. Genetic, biochemical, and molecular analyses indicate that this locus corresponds to an alpha(1,2)fucosyltransferase gene distinct from the genetically-linked H blood group alpha(1,2)fucosyltransferase locus. The accompanying paper (Rouquier, S., Lowe, J. B., Kelly, R. J., Fertitta, A. L., Lennon, G. G., and Giorgi, D. (1995) J. Biol. Chem. 270, 4632-4639) describes the molecular cloning and mapping of two human DNA segments that are physically linked to, and cross-hybridize with, the H locus. We present here an analysis of these two new DNA segments. One of these, termed Sec1, is a pseudogene, because translational frameshifts and termination codons interrupt potential open reading frames that would otherwise share primary sequence similarity with the H alpha(1,2)fucosyltransferase. The other DNA segment, termed Sec2, predicts a 332-amino acid-long polypeptide, and a longer isoform, that share 68% sequence identity with the COOH-terminal 292 residues of the human H blood group alpha(1,2)fucosyltransferase. Sec2 encodes an alpha(1,2)fucosyltransferase with catalytic properties that mirror those ascribed to the Secretor locus-encoded alpha(1,2)fucosyltransferase. Approximately 20% of randomly-selected individuals were found to be apparently homozygous for an enzyme-inactivating nonsense allele (Trp143-->ter) at this locus, in correspondence to the frequency of the non-secretor phenotype in most human populations. Furthermore, each of six unrelated non-secretor individuals are also apparently homozygous for this null allele. These results indicate that Sec2 corresponds to the human Secretor blood group locus (FUT2) and indicate that homozygosity for a common nonsense allele is responsible for the nonsecretor phenotype in many non-secretor individuals.
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To compare upper gastric endoscopic and histopathologic findings in older adults in the presence and absence of B12 deficiency. A prospective analysis of upper gastric endoscopic and gastric histopathologic findings from 30 newly identified B12-deficient patients (11 males, 19 females) and 16 controls with normal B12 status (6 males, 10 females) was performed. For all subjects, the indication for upper endoscopy and gastric biopsy were unrelated to B12 status. A single pathologist, blinded to B12 status, processed and interpreted the biopsy samples. Endoscopic and histopathologic findings were correlated with age, gender, hematocrit (Hct), MCV and B12 status. The B12-deficient group had significantly lower mean serum B12 levels compared to the controls (P<0.00005) while their mean Hct, MCV and serum albumin levels were similar. Iron deficiency (ferritin-based) was present in 21% of B12-deficient patients and intrinsic factor antibodies were present in 29% (5/17) of B12-deficient patients. The endoscopic findings revealed significantly different rates of gastritis and atrophy between the B12-deficient and control groups (P=0.017). B12-deficient patients had significantly less superficial gastritis (62% vs 94%) and significantly more atrophic gastritis (28% vs 0%) as compared to the controls (P=0.039). Intestinal metaplasia was similar in both groups. Helicobacter pylori infection rates were similar in the B12-deficient patients and controls (40% vs 31%). Significantly different endoscopic findings and types of gastritis could often be observed in the presence and absence of B12 deficiency. Atrophy, based on endoscopy, and atrophic gastritis, based on histopathology, suggest the presence of B12 deficiency. Gastric histopathology is not influenced by the age, gender, Hct or MCV of the patients.
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We conducted a genome-wide association study (GWAS) of breast cancer by genotyping 528,173 SNPs in 1,145 postmenopausal women of European ancestry with invasive breast cancer and 1,142 controls. We identified four SNPs in intron 2 of FGFR2 (which encodes a receptor tyrosine kinase and is amplified or overexpressed in some breast cancers) that were highly associated with breast cancer and confirmed this association in 1,776 affected individuals and 2,072 controls from three additional studies. Across the four studies, the association with all four SNPs was highly statistically significant (Ptrend for the most strongly associated SNP (rs1219648) = 1.1 10- 10; population attributable risk = 16%). Four SNPs at other loci most strongly associated with breast cancer in the initial GWAS were not associated in the replication studies. Our summary results from the GWAS are available online in a form that should speed the identification of additional risk loci.
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We performed studies in 25 patients with low serum cobalamin levels who had few if any clinical or hematologic findings of cobalamin deficiency. All but three had morphologically normoblastic hematopoiesis, and 15 were not even anemic. None of those tested excreted methylmalonic acid or homocystine. Nevertheless, the dUST identified metabolic abnormalities in 18 of the 25 cases. In vitro additives were essential in the dUST. Especially noteworthy was MTHF, whose addition unmasked an otherwise undetectable dUST abnormality in four cases. Why MTHF appears to act as a "stress test" in this setting is unknown but deserves further attention. Seven patients had early forms of classical malabsorptive states such as pernicious anemia, defined by abnormal Schilling test results. Among the rest, seven of 13 patients displayed malabsorption of protein-bound cobalamin despite normal absorption of free cobalamin by the Schilling test. In two patients, initially normal Schilling test results became abnormal the following year. These findings demonstrate that seemingly falsely low serum cobalamin levels often indicate subtle biochemical cobalamin deficiency. Early stages of pernicious anemia or other classical malabsorptive states are sometimes responsible for such subtle deficiency. However, malabsorption confined to protein-bound cobalamin is an equally common cause. Current concepts of cobalamin deficiency and the absorptive defects that can cause it should be expanded to include atypical defects requiring newer methods of identification.
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The coding sequences ( approximately 1 kb) of FUT2 [ABO-Secretor type alpha(1,2)fucosyltransferase] and of FUT6 [plasma alpha(1,3)fucosyltransferase] were analyzed for allelic polymorphism by direct sequencing in five populations. The nucleotide diversities of FUT2 estimated from pairwise sequence differences were 0.0045, 0.0042, 0.0042, 0.0009, and 0.0008 in Africans, European-Africans, Iranians, Chinese, and Japanese, respectively. The nucleotide diversities of FUT6 were 0.0024, 0.0016, 0.0015, 0.0017, and 0.0020 in Africans, European-Africans, Iranians, Chinese, and Japanese, respectively. At FUT2, excesses in pairwise sequence differences compared to the number of polymorphic sites as indicated by a significantly positive Tajima's D were observed in European-Africans and in Iranians. The data do not fit expectations of the equilibrium neutral model with an infinite number of sites. On the other hand, Tajima's D's at FUT6 in each of the five populations and at FUT2 in Africans, Chinese, and Japanese were not significantly different from zero. F(ST) between the Asians and the others measured at FUT2 was higher than at FUT6. These results suggest that natural selection was responsible for the generation of the FUT2 polymorphism in European-Africans and in Iranians.
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The aim of this study was to test the hypothesis that chronic atrophic gastritis induced by Helicobacter pylori (H. pylori) causes malabsorption of vitamin B12 and folate in food, leading ultimately to an increase in circulating homocysteine levels. We performed endoscopy with stomach biopsy and measured fasting plasma homocysteine, vitamin B12, and folate levels in 93 patients who underwent diagnostic coronary arteriography. The patients were divided into two groups according to the presence (n = 57) or absence (n = 36) of H. pylori infection. Positive H. pylori infection was defined as positive H. pylori histology of biopsy specimens from the stomach. The extent of atrophic gastritis was endoscopically graded from 0 to 6. There were no differences in age, sex, or traditional coronary risk factors between the two groups. Atrophy scores of the stomach were greater in patients with H. pylori infection than in patients without (3.9 +/- 1.4 vs 2.2 +/- 1.8, p < 0.0001). Patients with H. pylori infection had lower levels of vitamin B12 (630 +/- 222 vs 747 +/- 259 pg/ml, p = 0.02) and folate (6.2 +/- 2.1 vs 7.4 +/- 2.8, p = 0.046), as well as higher levels of homocysteine (11 +/- 4.9 vs 8.3 +/- 2.1 nmol/ml, p = 0.01), than did patients without H. pylori infection. Plasma homocysteine levels correlated inversely with plasma vitamin B12 and folate levels and positively with atrophic scores. This study suggests that H. pylori-induced chronic atrophic gastritis decreases plasma vitamin B12 and folic acid levels, thereby increasing homocysteine levels. However, this effect does not seem to be strong.
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Recent studies have suggested a relationship between Helicobacter pylori infection and various important micronutrients, including iron and vitamin B12, suggesting likely biological factors in the association between Helicobacter pylori and microcytic or macrocytic anaemia. There is some evidence that direct or indirect consequences of Helicobacter pylori gastritis on acid secretion account for the role of the bacterium in the absorption process of iron and Vitamin B12. The plasma, intragastric and mucosal concentration of different antioxidant compounds such as ascorbic acid, a-tocopherol and beta-carotene is also affected by Helicobacter pylori gastritis supporting the possible role of Helicobacter pylori in the multistep cascade leading to gastric carcinogenesis. The relationship between Helicobacter pylori infection and micronutrients is, therefore, a promising and, until now, poorly investigated field of research.
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Selective intestinal malabsorption of vitamin B(12) causing juvenile megaloblastic anemia (MGA; MIM# 261100) is a recessively inherited disorder that is believed to be rare except for notable clusters of cases in Finland, Norway, and the Eastern Mediterranean region. The disease can be caused by mutations in either the cubilin (CUBN; MGA1; MIM# 602997) or the amnionless (AMN; MIM# 605799) gene. To explain the peculiar geographical distribution, we hypothesized that mutations in one of the genes would mainly be responsible for the disease in Scandinavia, and mutations in the other gene in the Mediterranean region. We studied 42 sibships and found all cases in Finland to be due to CUBN (three different mutations) and all cases in Norway to be due to AMN (two different mutations), while in Turkey, Israel, and Saudi Arabia, there were two different AMN mutations and three different CUBN mutations. Haplotype evidence excluded both CUBN and AMN conclusively in five families and tentatively in three families, suggesting the presence of at least one more gene locus that can cause MGA. We conclude that the Scandinavian cases are typical examples of enrichment by founder effects, while in the Mediterranean region high degrees of consanguinity expose rare mutations in both genes. We suggest that in both regions, physician awareness of this disease causes it to be more readily diagnosed than elsewhere; thus, it may well be more common worldwide than previously thought.
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Both infection with Helicobacter pylori and alcohol abuse have been associated with low vitamin B12 serum levels. The interaction between both risk factors is unknown. The aim of this study was to determine whether Helicobacter pylori infection is associated with low vitamin B12 levels in alcohol dependent patients. Blood samples were obtained from adult alcohol dependent patients undergoing detoxification and analyzed for serum vitamin B12 levels. Helicobacter pylori infection was serologically measured. Patient characteristics, medication use and alcohol consumption at admission were assessed by interview. A total of 6 out of 89 patients included presented low vitamin B12 levels, all were sub clinical deficient (<250 pmol/L) and none were clinical deficient (<150 pmol/L). Infection with Helicobacter pylori was present in 29% of the patients. The average vitamin B12 levels in Helicobacter pylori seropositive and seronegative patients were 1,033 pmol/L (SD 741) and 971 pmol/L (SD 717), respectively. The relation between Helicobacter pylori infection and vitamin B12 deficiency was not of significance (OR=0.48; 95% CI [0.05-4.32]). In conclusion, Helicobacter pylori infection is not a risk factor for low vitamin B12 levels in alcohol dependent patients.
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The relation between B vitamins and cognitive decline is controversial. In this study, we explored the association of plasma folate and vitamin B12 with cognitive function measured approximately 10 years later. We determined plasma folate and vitamin B12 levels from blood samples collected in 1989 to 1990 and initially evaluated cognition in 1995 to 2001 among 635 women, age 70+ years, from the Nurses' Health Study. In a subset of 391, 3 repeated cognitive tests were completed for evaluation of cognitive decline over 4 years; repeated testing is ongoing for the remaining women. Our primary outcome was a global composite score of 6 neuropsychologic tests administered by telephone. We used linear regression models to estimate multivariable-adjusted mean cognitive performance across quartiles of the vitamins and longitudinal models for cognitive decline. Higher vitamin levels were not associated with either initial cognitive performance or subsequent cognitive decline. Mean difference in initial global score for top versus bottom quartiles was 0.06 standard units for folate (95% confidence interval [CI] = -0.10 to 0.22) and 0.15 units for vitamin B12 (0.00 to 0.31). There were no dose-response trends for either nutrient. Women with high levels of both nutrients initially performed better than women low in both nutrients (global score, mean difference = 0.34; 95% CI = 0.05 to 0.62); this association did not hold for subsequent cognitive decline. Combined B vitamin deficiency may be associated with impaired cognition, but in these healthy, well-nourished women, plasma folate and vitamin B12 were not related to cognitive function.