Helicobacter pylori serologic status has no influence on the association between fucosyltransferase 2 polymorphism (FUT2 461 G->A) and vitamin B-12 in Europe and West Africa

The Many Faces of Cobalamin (Vitamin B12) Deficiency

Although cobalamin (vitamin B₁₂) deficiency was described over a century ago, it is still difficult to establish the correct diagnosis and prescribe the right treatment. Symptoms related to vitamin B₁₂ deficiency may be diverse and vary from neurologic to psychiatric. A number of individuals with vitamin B₁₂ deficiency may present with the classic megaloblastic anemia.

In clinical practice, many cases of vitamin B₁₂ deficiency are overlooked or sometimes even misdiagnosed. In this review, we describe the heterogeneous disease spectrum of patients with vitamin B₁₂ deficiency in whom the diagnosis was either based on low serum B₁₂ levels, elevated biomarkers like methylmalonic acid and/or homocysteine, or the improvement of clinical symptoms after the institution of parenteral vitamin B₁₂ therapy. We discuss the possible clinical signs and symptoms of patients with B₁₂ deficiency and the various pitfalls of diagnosis and treatment.

Biomarkers of Nutrition for Development (BOND): Vitamin B-12 Review

This report on vitamin B-12 (B12) is part of the Biomarkers of Nutrition for Development (BOND) Project, which provides state-of-the art information and advice on the selection, use, and interpretation of biomarkers of nutrient exposure, status, and function. As with the other 5 reports in this series, which focused on iodine, folate, zinc, iron, and vitamin A, this B12 report was developed with the assistance of an expert panel (BOND B12 EP) and other experts who provided information during a consultation. The experts reviewed the existing literature in depth in order to consolidate existing relevant information on the biology of B12, including known and possible effects of insufficiency, and available and potential biomarkers of status. Unlike the situation for the other 5 nutrients reviewed during the BOND project, there has been relatively little previous attention paid to B12 status and its biomarkers, so this report is a landmark in terms of the consolidation and interpretation of the available information on B12 nutrition. Historically, most focus has been on diagnosis and treatment of clinical symptoms of B12 deficiency, which result primarily from pernicious anemia or strict vegetarianism. More recently, we have become aware of the high prevalence of B12 insufficiency in populations consuming low amounts of animal-source foods, which can be detected with ≥1 serum biomarker but presents the new challenge of identifying functional consequences that may require public health interventions.

Should vitamin B12 status be considered in assessing risk of neural tube defects?

There is a strong biological premise for including vitamin B₁₂ with folic acid in strategies to prevent neural tube defects (NTDs), due to the closely interlinked metabolism of these two vitamins. For example, reduction of B₁₂ deficiency among women of reproductive age could enhance the capacity of folic acid to prevent NTDs by optimizing the cellular uptake and utilization of natural folate cofactors. Vitamin B₁₂ might also have an independent role in NTD prevention, such that adding it in fortification programs might be more effective than fortifying with folic acid alone. Globally, there is ample evidence of widespread vitamin B₁₂ deficiency in low‐ and middle‐income countries, but there is also considerable divergence of vitamin B₁₂ status across regions, likely due to genetic as well as nutritional factors. Here, I consider the evidence that low vitamin B₁₂ status may be an independent factor associated with risk of NTDs, and whether a fortification strategy to improve B₁₂ status would help reduce the prevalence of NTDs. I seek to identify knowledge gaps in this respect and specify research goals that would address these gaps.

Association of combined GIF290T>C heterozygous mutation/FUT2 secretor variant with neural tube defects

Folate and vitamin B12 are needed for the proper embryo-fetal development possibly through their interacting role in the 1-carbon metabolism. Folate fortification reduces the prevalence of complex birth defects, and more specifically neural tube defects (NTDs). GIF and FUT2 are 2 genes associated with the uptake and blood level of vitamin B12. We evaluated GIF and FUT2 as predictors of severe birth defects, in 183 aborted fetuses compared with 375 healthy newborns. The GIF290C allele frequency was estimated to 0.4% in healthy newborns and to 8.1% in NTD fetuses (odds ratio 17.8 [95% confidence interval CI: 4.0-77.6]). The frequency of FUT2 rs601338 secretor variant was not different among groups. The GIF 290C heterozygous/FUT2 rs601338 secretor variant combined genotype was reported in 6 of the 37 NTD fetuses, but not in other fetuses and healthy newborns (P < .0001). This GIF/FUT2 combined genotype has been previously reported in children with congenital gastric intrinsic factor (GIF) deficiency, with respective consequences on B12 binding activity and GIF secretion. In conclusion, a genotype reported in congenital GIF deficiency produces also severe forms of NTD. This suggests that vitamin B12 delivery to neural tissue by the CUBN/GIF pathway could play a role in the neural tube closure mechanisms.

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

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.

Whole Genome Sequencing of Mycobacterium africanum Strains from Mali Provides Insights into the Mechanisms of Geographic Restriction

Background

Mycobacterium africanum, made up of lineages 5 and 6 within the Mycobacterium tuberculosis complex (MTC), causes up to half of all tuberculosis cases in West Africa, but is rarely found outside of this region. The reasons for this geographical restriction remain unknown. Possible reasons include a geographically restricted animal reservoir, a unique preference for hosts of West African ethnicity, and an inability to compete with other lineages outside of West Africa. These latter two hypotheses could be caused by loss of fitness or altered interactions with the host immune system.

Methodology/Principal Findings

We sequenced 92 MTC clinical isolates from Mali, including two lineage 5 and 24 lineage 6 strains. Our genome sequencing assembly, alignment, phylogeny and average nucleotide identity analyses enabled us to identify features that typify lineages 5 and 6 and made clear that these lineages do not constitute a distinct species within the MTC. We found that in Mali, lineage 6 and lineage 4 strains have similar levels of diversity and evolve drug resistance through similar mechanisms. In the process, we identified a putative novel streptomycin resistance mutation. In addition, we found evidence of person-to-person transmission of lineage 6 isolates and showed that lineage 6 is not enriched for mutations in virulence-associated genes.

Conclusions

This is the largest collection of lineage 5 and 6 whole genome sequences to date, and our assembly and alignment data provide valuable insights into what distinguishes these lineages from other MTC lineages. Lineages 5 and 6 do not appear to be geographically restricted due to an inability to transmit between West African hosts or to an elevated number of mutations in virulence-associated genes. However, lineage-specific mutations, such as mutations in cell wall structure, secretion systems and cofactor biosynthesis, provide alternative mechanisms that may lead to host specificity.

Mycobacterium africanum consists of two lineages, lineages 5 and 6, within the Mycobacterium tuberculosis complex (MTC) that cause human tuberculosis in West Africa, but are found rarely outside of this region. Our analysis of the whole genome sequences of 26 lineage 5 and 6 isolates, and 66 isolates from other lineages within the MTC, reveal that M. africanum does not meet modern criteria to be considered an independent species. We analyzed drug resistance-associated genes and found that drug resistance evolves within these lineages through similar mechanisms as observed for the rest of the MTC in Mali. Though we did not see an elevated number of mutations in virulence-associated genes in these two lineages, we identified a number of lineage-specific mutations, pseudogenes and changes in gene content that may impact virulence and host specificity, and improve, overall, our understanding of what make these lineages unique.

Fucosyltransferase 2: a genetic risk factor for primary sclerosing cholangitis and Crohn's disease--a comprehensive review

Fucosyltransferase 2 (FUT2) mediates the inclusion of fucose in sugar moieties of glycoproteins and glycolipids. ABO blood group antigens and host-microbe interactions are influenced by FUT2 activity. About 20 % of the population has a "non-secretor" status caused by inactivating variants of FUT2 on both alleles. The non-sense mutation G428A and the missense mutation A385T are responsible for the vast majority of the non-secretor status in Caucasians, Africans, and Asians, respectively. Non-secretor individuals do not secrete fucose-positive antigens and lack fucosylation in epithelia. They also appear to be protected against a number of infectious diseases, such as Norovirus and Rotavirus infections. In recent years, genome-wide association studies (GWAS) identified inactivating variants at the FUT2 locus to be associated with primary sclerosing cholangitis (PSC), Crohn's disease (CD), and biochemical markers of biliary damage. These associations are intriguing given the important roles of fucosylated glycans in host-microbe interactions and membrane stability. Non-secretors have a reduced fecal content of Bifidobacteria. The intestinal bacterial composition of CD patients resembles the one of non-secretors, with an increase in Firmicutes and decreases in Proteobacteria and Actinobacteria. Non-secretor individuals lack fucosylated glycans at the surface of biliary epithelium and display a different bacterial composition of bile compared to secretors. Notably, an intact biliary epithelial glycocalix is relevant for a stable 'biliary HCO3 (-) umbrella' to protect against toxic effects of hydrophobic bile salt monomers. Here, the biology of FUT2 will be discussed as well as hypotheses to explain the role of FUT2 in the pathophysiology of PSC and Crohn's disease.

Exome-Wide Association Study Identifies New Low-Frequency and Rare UGT1A1 Coding Variants and UGT1A6 Coding Variants Influencing Serum Bilirubin in Elderly Subjects: A Strobe Compliant Article

Genome-wide association studies (GWASs) have identified loci contributing to total serum bilirubin level. However, no exome-wide approaches have been performed to address this question. Using exome-wide approach, we assessed the influence of protein-coding variants on unconjugated, conjugated, and total serum bilirubin levels in a well-characterized cohort of 773 ambulatory elderly subjects from Italy. Coding variants were replicated in 227 elderly subjects from the same area. We identified 4 missense rare (minor allele frequency, MAF < 0.5%) and low-frequency (MAF, 0.5%-5%) coding variants located in the first exon of the UGT1A1 gene, which encodes for the substrate-binding domain (rs4148323 [MAF = 0.06%; p.Gly71Arg], rs144398951 [MAF = 0.06%; p.Ile215Val], rs35003977 [MAF = 0.78%; p.Val225Gly], and rs57307513 [MAF = 0.06%; p.Ser250Pro]). These variants were in strong linkage disequilibrium with 3 intronic UGT1A1 variants (rs887829, rs4148325, rs6742078), which were significantly associated with total bilirubin level (P = 2.34 × 10(-34), P = 7.02 × 10(-34), and P = 8.27 × 10(-34)), as well as unconjugated, and conjugated bilirubin levels. We also identified UGT1A6 variants in association with total (rs6759892, p.Ser7Ala, P = 1.98 × 10(-26); rs2070959, p.Thr181Ala, P = 2.87 × 10(-27); and rs1105879, p.Arg184Ser, P = 3.27 × 10(-29)), unconjugated, and conjugated bilirubin levels. All UGT1A1 intronic variants (rs887829, rs6742078, and rs4148325) and UGT1A6 coding variants (rs6759892, rs2070959, and rs1105879) were significantly associated with gallstone-related cholecystectomy risk. The UGT1A6 variant rs2070959 (p.Thr181Ala) was associated with the highest risk of gallstone-related cholecystectomy (OR, 4.58; 95% CI, 1.58-13.28; P = 3.21 × 10(-3)). Using an exome-wide approach we identified coding variants on UGT1A1 and UGT1A6 genes in association with serum bilirubin level and hyperbilirubinemia risk in elderly subjects. UGT1A1 intronic single-nucleotide polymorphisms (SNPs) (rs6742078, rs887829, rs4148324) serve as proxy markers for the low-frequency and rare UGT1A1 variants, thereby providing mechanistic explanation to the relationship between UGT1A1 intronic SNPs and the UGT1A1 enzyme activity. UGT1A1 and UGT1A6 variants might be potentially associated with gallstone-related cholecystectomy risk.

Genetic and environmental factors associated with vitamin B12status in Amazonian children

Objective

To evaluate the prevalence of vitamin B12deficiency and factors associated with vitamin B12status in Amazonian children.

Design

Genetic risk score (GRS), socio-economic and nutritional status, and morbidity data were the independent variables used in multiple linear regression models to evaluate factors associated with vitamin B12status in a population-based cross-sectional study. GRS was created by summing a number of known risk alleles for low serum vitamin B12.

Setting

Acrelândia, western Brazilian Amazon.

Subjects

Children (n988) aged <10 years.

Results

Overall prevalence of vitamin B12deficiency (<150 pmol/l) was 4·2 (95 % CI 3·0, 5·6) % and was highest in children aged <24 months: 13·6 (95 % CI % 8·8, 19·7) %. For children <24 months, wealth index (β=0·017,P=0·030) and animal protein intake(β=0·219,P=0·003) were positively associated with vitamin B12status. GRS (β=−0·114,P<0·001) and serum homocysteine (β=–0·049,P<0·001) were negatively associated. Among children aged ≥24 months, vitamin B12status was positively associated with wealth index (β=0·012,P<0·001), height-for-ageZ-score (β=0·024, P=0·033) and serum vitamin A (β=0·089,P<0·001). Age≥60 months(β=–0·118,P<0·001), GRS (β=–0·048, P<0·001), maternal schooling <5 years (β=–0·083,P<0·001), low intake of animal-derived foods (β=–0·050,P=0·030), serum homocysteine (β=–0·053,P<0·001), serum folate ≥23·6 nmol/l (β=–0·055,P=0·012) and geohelminth infection (β=–0·141,P=0·017) were negatively associated with vitamin B12status.

Conclusions

GRS, poverty, low intake of animal-derived foods, geohelminth infection, vitamin A and folate status were important factors associated with vitamin B12status of children in our study.

Modeling a methylmalonic acid-derived change point for serum vitamin B-12 for adults in NHANES

BACKGROUND

No consensus exists about which cutoff point should be applied for serum vitamin B-12 (SB-12) concentrations to define vitamin B-12 status in population-based research.

OBJECTIVE

The study's aim was to identify whether a change point exists at which the relation between plasma methylmalonic acid (MMA) and SB-12 changes slope to differentiate between inadequate and adequate vitamin B-12 status by using various statistical models.

DESIGN

We used data on adults (≥19 y; n = 12,683) from NHANES 1999-2004-a nationally representative, cross-sectional survey. We evaluated 6 piece-wise polynomial and exponential decay models that used different control levels for known covariates.

RESULTS

The MMA-defined change point for SB-12 varied depending on the statistical model used. A linear-splines model was determined to best fit the data, as determined by the approximate permutation test; 3 slopes relating SB-12 and MMA and resulting in 2 change points and 3 subgroups were shown. The first group (SB-12 <126 pmol/L) was small and had the highest MMA concentration (median: 281 nmol/L; 95% CI: 245, 366 nmol/L; n = 157, 1.2%); many in this group could be considered at high risk of severe deficiency because combined abnormalities of MMA and homocysteine were very frequent and the concentrations themselves were significantly higher. The highest SB-12 group (SB-12 >287 pmol/L; n = 8569, 67.6%) likely had adequate vitamin B-12 status (median MMA: 120 nmol/L; 95% CI: 119, 125 nmol/L). The vitamin B-12 status of the sizable intermediate group (n = 3957, 33%) was difficult to interpret.

CONCLUSIONS

The 3 distinct slopes for the relation between SB-12 and MMA challenges the conventional use of one cutoff point for classifying vitamin B-12 status. In epidemiologic research, the use of one cutoff point would fail to separate the small, severely deficient group from the intermediate group that has neither normal nor clearly deficient vitamin B-12 concentrations (ie, unknown vitamin B-12 status). This intermediate group requires further characterization.

Gastric intrinsic factor deficiency with combined GIF heterozygous mutations and FUT2 secretor variant

Several genome-wide association studies (GWAS) have identified a strong association between serum vitamin B12 and fucosyltransferase 2 (FUT2), a gene associated with susceptibility to Helicobacter pylori infection. Hazra et al. conducted a meta-analysis of three GWAS and found three additional loci in MUT, CUBN and TCN1. Other GWAS conducted in Italy and China confirmed the association for FUT2 gene. Alpha-2-fucosyltransferase (FUT2) catalyzes fucose addition to form H-type antigens in exocrine secretions. FUT2 non-secretor variant produces no secretion of H-type antigens and is associated with high-plasma vitamin B12 levels. This association was explained by the influence of FUT2 on H. pylori, which is a risk factor of gastritis, a main cause of vitamin B12 impaired absorption. However, we recently showed that H. pylori serology had no influence on FUT2 association with vitamin B12, in a large sample population, suggesting the involvement of an alternative mechanism. GIF is another gene associated with plasma levels of vitamin B12 and gastric intrinsic factor (GIF) is a fucosylated protein needed for B12 absorption. Inherited GIF deficiency produces B12 deficiency unrelated with gastritis. We report 2 families with heterozygous GIF mutation, 290T>C, M97T, with decreased binding affinity of GIF for vitamin B12 and one family with heterozygous GIF mutation 435_437delGAA, K145_N146delinsN and no B12 binding activity of mutated GIF. All cases with vitamin B12 deficit carried the FUT2 rs601338 secretor variant. Ulex europeus binding to GIF was influenced by FUT2 genotypes and GIF concentration was lower, in gastric juice from control subjects with the secretor genotype. GIF290C allele was reported in 5 European cases and no Africans among 1282 ambulatory subjects and was associated with low plasma vitamin B12 and anaemia in the single case bearing the FUT2 secretor variant. We concluded that FUT2 secretor variant worsens B12 status in cases with heterozygous GIF mutations by impairing GIF secretion, independently from H. pylori-related gastritis.