The contribution folate and vitamin B12 genes to disease.

叶酸和维生素 B12 基因对疾病的贡献。

• 批准号: 10700697
• 负责人: Lawrence C Brody
• 金额: $ 53.06万
• 依托单位: NATIONAL HUMAN GENOME RESEARCH INSTITUTE
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10700697
• 关键词: Affect; Affinity; Age; Anemia; Animal Model; Animals; Binding; Bioinformatics; Biological; Biological Assay; Biology; Blood; Brain; Carbon; Caring; Carrier Proteins; Cell division; Cells; Choline; Clinical; Code; Cohort Studies; Collaborations; Congenital Abnormality; DNA; DNA Methylation; Defect; Deposition; Development; Diet; Disease; Embryo; Environmental Exposure; Environmental Risk Factor; Equilibrium; Exhibits; Female; Fishes; Folic Acid; Folic Acid Deficiency; Frequencies; Funding; Future; Gene Expression; Genes; Genetic; Genetic Predisposition to Disease; Genetic Research; Genetic Variation; Genotype; Glycine; Goals; Hair Color; Health; Heart Diseases; Homocysteine; Human; Human Genome; Impaired cognition; Individual; Infertility; Inherited; Injections; International; Knock-out; Length; Literature; Liver; Location; Malignant Neoplasms; Measures; Metabolic; Metabolic Pathway; Metabolism; Methionine; Methods; Methylmalonic Acid; Micronutrients; Mitochondria; Modeling; Mus; Nervous System Physiology; Neural Tube Defects; Neurologic; Normal Range; Nutrient; Other Genetics; Pathway interactions; Population; Pregnancy; Process; Proteins; Publishing; Reporting; Research; Research Personnel; Retina; Risk; Role; Sample Size; Sampling; Side; Spinal Dysraphism; System; Testing; Tissues; Transcobalamins; Variant; Vitamin B 12; Vitamin B 12 Deficiency; Vitamin B6; Work; Zebrafish; anxious behavior; cell growth; cellular targeting; circulating biomarkers; college; cost; experimental study; fetus nutrition; gene environment interaction; genetic variant; genome wide association study; genotyping technology; implantation; insight; melanocyte; mouse model; offspring; recruit; research clinical testing; tumor; uptake; vitamin receptor; whole genome

Research in the Gene and Environment Interaction Section is focused on defining changes in the genes that underlie inherited susceptibilities to common diseases such as cancer and birth defects. Changes in folate and vitamin B12 metabolism are associated with tumor formation, birth defects and cognitive decline. Folate and vitamin B12 genes are also involved in the methylation of DNA and normal brain function. We are searching for genetic variants in genes related to folate, methionine and homocysteine metabolism. Individuals affected with spina bifida (one form of neural tube defects) will be tested for these variants. Variants found at higher frequency in individuals with disease will help us identify genes associated with risk. The field of neural tube defects has historically focused on evaluating variation in genes in the folate/vitamin B12 metabolic pathway (e.g., DHFR2, published in 2021). As genotyping technology has increasingly offered more information at lower cost, the next logical step in this research is to screen the entire genome for additional genes associated with NTDs. This type of experiment requires a very large sample size. Although we have one of the worlds largest samples of NTDs that are available for genetic research, our sample is too small to carry out a genome wide association study (GWAS). In collaboration with Anne Molloy, Trinity College Dublin, we have organized an international collaboration with the goal of pooling samples for a GWAS. Over ten groups have joined this collaborative effort. The total number of samples collected by all groups exceeds 10,000 and includes nearly 3000 cases. We have obtained external funding to coordinate this study and collect the samples at a central location. We have collected DNA samples from these collaborators, and in the past year we have continued recruitment of additional investigator participation in replication studies. The majority of these samples have been submitted to the genotyping center for pretesting and the remainder are currently being arrayed for genotyping. Other groups have measured the impact of genetic variants on the level of total vitamin B12 in blood. We have measured vitamin B12 in the blood of over 2,000 individuals using standard methods. We then subjected these samples to assays that resolve circulating vitamin B12 into pools that correspond to its two major carrier proteins; transcobalamin, the bioactive carrier that is taken up by all cells, or haptocorrin, which is taken up by the liver for eventual recirculation or elimination. We previously published our work describing our insight that the variant repeatedly reported to influence circulating vitamin B12 is actually influencing the subset of vitamin B12 bound to haptocorrin (Velkova 2017). In a previous study of this cohort (Molloy 2016), we published that the common genetic variant most associated with a circulating marker of vitamin B12 deficiency was in a gene unrelated to vitamin B12 transport or metabolism. These findings could be relevant to clinical measures of vitamin B12 testing where it is known that individuals on either side of the normal range are given false positive and negative results. It may be possible to use individual genetic variation to refine the interpretation of clinical testing. In addition to vitamin B12, we have recently published on genetic influence on other circulating metabolites related to the folate one-carbon metabolic pathway. Such variants may be part of the normal population variation and still, in combination with other genetic and environmental factors, contribute to disease states. We have collaborated to publish on genetic variants influencing formate (Brosnan 2018), glycine (OReilly 2018), folate and homocysteine (Shane 2018), and most recently vitamin B6 (Stevelink 2019). Our recent collaboration seeking to determine whether a variant we identified as influencing circulating levels of bioavailable vitamin B12 might have clinical consequence has been recently published (Pangilinan 2021). We have additionally been evaluating which genetic variants most influence mitochondrial metabolites related to the one-carbon metabolic pathway. This has led to a new collaboration to determine whether a gene harboring a variant that influences choline might in fact be it as-yet unidentified transporter. We are also using animal models to understand the biology of genes involved in vitamin B12 metabolism. We have developed strains of zebrafish and mice in which we have disrupted vitamin B12 transport genes. In our zebrafish model, we targeted the only known circulatory carrier of vitamin B12, Tcn2. Although these fish should not be able to deliver vitamin B12 to their cells and tissue, they appear to develop normally. This led to a search for an alternate vitamin B12 transport protein in zebrafish. A bioinformatics approach revealed two coding regions that are highly similar to the known carrier protein. We have shown that in an artificial system these partial proteins can be expressed and bind vitamin B12 with affinities comparable to known carrier proteins. These proteins may have a biological role in vitamin B12 transport in these fish. This work has been published (Benoit 2018). Since then, we have additionally characterized the effect of knocking out the Tcn2 in zebrafish (Benoit 2021). Without this vitamin B12 transporter, zebrafish exhibit a shorter body length but otherwise appear normal. However, female fish without Tcn2 give rise to offspring with gross developmental and metabolic defects. Since this is observed regardless of the paternal genotype, this seems to be a maternal effect. We speculate that these female fish without Tcn2 may not be able to deposit sufficient vitamin B12 into the yolk for normal development. Despite the lack of maternal care, these animals could serve as a model maternal-fetal nutrition. Our other model of vitamin B12 deficiency is in mice, where we have targeted the cellular receptor for vitamin B12 uptake. These animals appear to mimic a number of aspects of vitamin B12 deficiency in humans, especially when placed on a diet lacking vitamin B12. First, these mice exhibit the metabolic hallmarks of vitamin B12 deficiency observed in humans (elevated circulating homocysteine and methylmalonic acid). They are also prone to developing anemia as they age, which can be temporarily rescued with an injection of vitamin B12. Last, we have been investigating female-specific infertility in these mice. These dams appear to ovulate normally, and we have shown their embryos can develop for a few days but implantation is generally unsuccessful. Maternal injections of vitamin B12 restore the ability of these dams to sustain a pregnancy. This work has been published (Bernard 2018). Future work is needed to determine whether vitamin B12 deficiency in the offspring also contributes to the apparent infertility of their dams. In the past year we have been exploring the impact of vitamin B12 deficiency on neurological function (gene expression in the brain, ability to sense heat, balance, and anxious behaviors) and retinal health. Future work with this animal model may include interrogating the effect of vitamin B12 deficiency on cell division (e.g., melanocyte activity as it relates to hair color). The literature contains a variety of strength of evidence of the impact of vitamin B12 on these aspects of human health, and our mouse model provides a way to more fully interrogate these processes.

基因与环境相互作用科的研究重点是确定基因的变化，这些变化是癌症和出生缺陷等常见疾病遗传易感性的基础。叶酸和维生素B12代谢的变化与肿瘤形成、出生缺陷和认知能力下降有关。叶酸和维生素B12基因也与DNA甲基化和正常脑功能有关。我们正在寻找与叶酸、蛋氨酸和同型半胱氨酸代谢有关的基因的遗传变异。患有脊柱裂（神经管缺陷的一种形式）的个体将接受这些变异的检测。在患病个体中发现的频率更高的变异将帮助我们识别与风险相关的基因。