- freely available
Nutrients 2013, 5(9), 3531-3550; doi:10.3390/nu5093531
Published: 10 September 2013
Abstract: Vitamin B12 (cobalamin, Cbl) is required for cellular metabolism. It is an essential coenzyme in mammals for two reactions: the conversion of homocysteine to methionine by the enzyme methionine synthase and the conversion of methylmalonyl-CoA to succinyl-CoA by the enzyme methylmalonyl-CoA mutase. Symptoms of Cbl deficiency are hematological, neurological and cognitive, including megaloblastic anaemia, tingling and numbness of the extremities, gait abnormalities, visual disturbances, memory loss and dementia. During pregnancy Cbl is essential, presumably because of its role in DNA synthesis and methionine synthesis; however, there are conflicting studies regarding an association between early pregnancy loss and Cbl deficiency. We here review the literature about the requirement for Cbl during pregnancy, and summarized what is known of the expression pattern and function of genes required for Cbl metabolism in embryonic mouse models.
Over the last two decades, there has been great interest of the role that nutritional factors such as folates and vitamin B12, play during embryonic development. One of the most prominent examples linking vitamins to development is the finding that the maternal periconceptional supplementation with folates can prevent occurrence and recurrence of neural tube defects [1,2]. However, even in the presence of folic acid fortification neural tube defects continue to occur [2,3], and thus interest in other interventions that could further reduce the prevalence of these disorders has increased. Vitamin B12, or cobalamin (Cbl), has also been identified as a crucial nutrient for foetal development [3,4]. The metabolisms of Cbl and folate are interrelated, with some of the biochemical and clinical effects of Cbl deficiency mediated by a functional deficiency of folate cofactors required for de novo nucleotide synthesis. A series of inborn errors of Cbl metabolism have been described, leading to identification of a number of genes encoding proteins involved in cellular Cbl metabolism. These inborn errors result in elevation of either homocysteine or methylmalonic acid, or both, in blood and urine, and can lead to human birth defects, including cardiovascular defects and facial dysmorphology.
Several studies have linked Cbl deficiency with increased risk of intrauterine growth retardation, abnormal embryo-foetal brain development, cleft palate and metabolic syndromes [3,5,6,7]. As deficiency of either folate or Cbl can result in similar biochemical effects, it has been suggested that a combined deficiency of Cbl and folate contribute to neural tube defects (NTD) and other birth defects. However, definitive proof of this hypothesis is lacking. In addition, although Cbl is also required for normal embryonic development in animal models, further studies are necessary to fully explain differences between findings in animal models and human patients with Cbl deficiency. In this manuscript we summarize what is known of the expression pattern of genes required for Cbl metabolism in the mouse model, and reviewed the literature in relation to the requirement for Cbl in human and mouse models.
2. Transport and Metabolism of Cobalamin
Cbl is required for cellular metabolism, and is obtained from the diet and found exclusively in animal products. Cbl contains the physiologically rare element, cobalt. The cobalt atom is surrounded by a corrin ring and upper and lower axial ligands. The lower axial ligand is an unusual ribonucleoside, dimethylbenzimidazole (DMB), which can be found in the base-on, or base-off conformation. In the base-on conformation the ligand is attached to the central cobalt atom, whereas in the base-off conformation the ligand is displaced from cobalt. The base-on and base-off conformations appear to play a role in the stability of different forms of Cbl, as well as their ability to bind to proteins .
Human uptake of Cbl is complex, requiring three Cbl binding proteins: intrinsic factor, haptocorrin and transcobalamin. Food-bound Cbl is released in the stomach where it is subsequently bound by haptocorrin (HC) . Cbl is released from HC by pancreatic protease digestion in the jejunum, where it is bound by intrinsic factor (IF), to form an IF-Cbl complex. The IF-Cbl complex is bound by the cubam receptor, formed by two proteins amnionless and cubilin, which aids in the endocytosis of IF-Cbl into ileal enterocytes [10,11]. Dissociation of IF-Cbl complex occurs in the lysosome of enterocytes. Then, Cbl is exported into the portal circulation by the ATP-binding cassette (ABC) transporter ABCC1 (MRP1). Newly-absorbed Cbl appears in the portal circulation bound to transcobalamin (TC).
In cells the TC-Cbl complex is recognized by the transcobalamin receptor CD 320 . Once the TC-Cbl complex binds the TC receptor on the cell surface, a process of receptor-mediated endocytosis is triggered. The endocytic vesicle is directed to the lysosomal pathway and the lysosomal proteases of the compartment leads to a dissociation of the complex [13,14]. Free Cbl is translocated to the cytoplasm by two proteins: LMBD1 [15,16,17,18,19,20,21,22] and ABCD4 . Once inside the cytoplasm, the central cobalt atom of Cbl must be reduced, and this process is thought to be aided by MMACHC and MMADHC proteins. MMACHC protein has a Cbl binding site and a TonB like domain . MMACHC removes the upper axial ligand of dietary Cbl by reductive decyanation of CNCbl  or by dealkylation of either MeCbl or AdoCbl . It has been postulated that MMACHC is the immediate downstream acceptor of the Cbl exiting the lysosome. MMACHC interacts with MMADHC, which presents Cbl to the cytosolic and mitochondrial proteins  acting as a branch point for Cbl delivery to the cytoplasm and mitochondria. However, the factors that determine the distribution of MMADHC between the cytoplasm and mitochondria remain unknown. Cbl can be converted to methylcobalamin (MeCbl), a coenzyme for methionine synthase (MS) in the cytosol, or 5-deoxyadenosylcobalamin (AdoCbl), a coenzyme for l-methylmalonyl-CoA mutase (MUT, MCM) in the mitochondria. In the cytosol, MS encoded by the MTR gene catalyzes the methylation of homocysteine to form methionine using 5-methyltetrahydrofolate as a methyl donor. In this reaction, MeCbl is the transient acceptor of the methyl group, with cycling of Cbl between its fully reduced cob(I)alamin and MeCbl forms. Methionine synthase reductase (MSR) encoded by the MTRR gene is required to maintain MS-bound Cbl in its active form by reducing partially-oxidized cob(II)alamin to MeCbl, with the transfer of a methyl group from adenosylmethionine. In the mitochondria, the MMAA protein binds to MCM and acts as a chaperone to prevent MCM inactivation [28,29]. The MMAB protein (ATP:cob(I)alamin adenosyltransferase) catalyzes the final step of AdoCbl biosynthesis [30,31]. In addition to converting the reduced form of Cbl into AdoCbl, the MMAB protein may also act as a chaperone ensuring AdoCbl’s delivery to its target, MCM . In summary, Cbl is necessary for: (i) the remethylation of homocysteine and the production of methionine, the precursor of S-adeno-sylmethionine (SAM). SAM is the major donor of methyl groups for many substrates such as: DNA, RNA, histones and co-regulators of nuclear receptors that plays a key role in epigenetic and epigenomic mechanisms and (ii) the metabolism of branched chain amino acids, odd-chain fatty acids and cholesterol and catalyzes the reversible isomerization of l-methylmalonyl-CoA to l-succinyl-CoA, which is key to the breakdown of propionate as well as for replenishing the TCA cycle (Figure 1).
3. Cobalamin Deficiency, Polymorphism and Risk of Neural Tube Defects
Cbl deficiency, in association with folate deficiency is potentially a health problem during pregnancy. Human studies are numerous and the results are interesting although not conclusive. Low concentrations of Cbl in the mother’s serum have been linked with increased risk of neural tube defects, (NTD) in Irish, Canadian, Chinese, and Egyptian populations [33,34,35,36,37]. However, other studies have found no effect of Cbl status [38,39,40,41,42,43,44,45,46,47]. These results have been reviewed by Ray and Blom 2003, who identified a moderate association between low maternal serum Cbl levels and risk of NTD . In amniotic fluid from neural tube defect pregnancies, Cbl levels have been measured, and in most cases have been lower in affected pregnancies compared to controls [39,49,50,51,52,53,54]. However, in mothers who previously had a child with NTD there was no difference in Cbl levels in amniotic fluid compared to controls .
Holotranscobalamin (holoTC; Cbl bound to TC), is the fraction of circulating Cbl that is available for tissue uptake. Decreased levels of holoTC were observed in the serum of mothers who had a child with NTD [55,56] or who were pregnant with a NTD fetus . In addition, the levels of apo-haptocorrin and apo-TC were doubled and tripled respectively in amniotic fluid from pregnant women who had a child with NTD compared with control groups , suggesting that holoTC is a better reflector of Cbl status [57,58]. This is in contrast to the findings of AlAisari et al., who showed that holoTC and total Cbl, alone and in combination, have almost equal diagnostic efficiency in screening/diagnosing Cbl status in patients investigated for Cbl deficiency . The Cbl status of mothers with infants with cleft lip or palate has not been extensively analyzed. One study of serum Cbl in mothers who had delivered a child with cleft lip showed a significant decrease in Cbl levels compared to controls , but not all studies show the same results [61,62]. Elevated propionylcarnitine in infants is a marker of maternal Cbl deficiency when total blood propionylcarnitine concentrations were measured in newborns with orofacial clefts, the authors did not find any significant differences in the mean concentrations between newborns with clefts and controls, suggesting that the deficiency of Cbl seems not to be a risk factor for CLP .
Human studies also have shown a link between polymorphisms in genes involved in Cbl transport and metabolism with the risk of developing neural tube defects. A polymorphism (rs1907362) in the 27th intron of the CUBN gene has been linked with a decreased risk of spina bifida, and was related to increased serum Cbl levels . A polymorphism in the MTRR gene (c.66A>G) has been associated with an increased risk of developing a NTD in offspring, with the GG or AG polymorphism [64,65,66,67,68,69]. In contrast, two studies appeared to demonstrate a protective effect of the G allele [70,71]. Other studies have not shown any effect on neural tube defect risk [49,72,73,74,75] or risk of other birth defects [49,72,76]. Polymorphisms in the MTR gene (2756A>G; 2758C>G) result in various health problems before birth [64,69,70,77]. However, no association has been found between these polymorphisms and increased maternal risk for giving birth to children with NTD . The 776C>G polymorphism in the TCN2 gene has been linked with increased risk of NTD-affected pregnancy in Irish and Italian populations [79,80] and the association of the G allele with spina bifida has been reported . Significant over transmission of the TCN2 C allele in offspring with cleft lip with or without cleft palate has been observed .
4. Expression Pattern of Cbl Genes during Mouse Organogenesis
In the hope of identifying the etiology of developmental abnormalities and possible maternal contribution to the phenotypes associated with Cbl metabolism, we, and others, have evaluated the expression pattern of the genes associated with Cbl metabolism (Mmaa, Mmab, Mmachc, Mmadhc, Mtr, Mtrr, Lmbrd1, Abcd4 and Mut) by in situ hybridization and immunohistochemistry in wild type mouse placentas and embryos [82,83,84,85,86,87,88].
The expression patterns of Mtr, Mmaa, Mmab and Mut were analyzed at several stages of placental development. Mtr was highly expressed in syncytiotrophoblast cells of the labyrinth (functional) layer and trophoblast giant cells of the mouse placenta. The strongest expression of Mtr was between embryonic day (E) E9.5–E12.5. At these stages, Mtr was expressed in the S-TGC that lines the maternal sinuses and provides endocrine support for the pregnancy. Mtr was also highly expressed in parietal trophoblast giant cells (P-TGCs) between E8.5–E10.5. The P-TGC serves to separate the embryonic portion of the placenta from the maternal decidua. In addition, Mtr was highly expressed in very invasive trophoblast giant cells such as canal trophoblast giant cells (C-TGCs) that lines the maternal vessels which bring blood to the placenta, and in glycogen trophoblast (GlyT) cells at E12.5, E15.5 and E18.5 . We reported broad expression of Mmaa, and Mmab in the labyrinth layer, giant cells and spongiotrophoblast cells of placentas from E10.5 embryos. In contrast, we did not find high expression of Mut in the placenta . The expression patterns observed in the placenta suggest that Mtr, Mmaa, and Mmab may be important for normal Cbl metabolism in the placenta. It will be interesting to determine if proteins required for Cbl uptake are also expressed in the placenta as this might suggest that Cbl is not only transported across the placental barrier but is utilized in this organ.
The expression patterns of Abcd4, Mmachc, Mmadhc, Mtrr, Mtr, Mmaa, Mmab and Mut have been reported during different stages of mouse development. At E14.5, the only stage analyzed, Abcd4 was expressed in the central nervous system, telecephalon, and neocortex . Expression of Abcd4 was also detected in the mantle layer of the cerebral cortex . Intriguingly, expression of this gene has not been reported outside of the nervous system.
Mmachc and Mmadhc expression was analyzed at E11.5. Unlike Abcd4, these genes were broadly expressed in most organs. Mmachc and Mmadhc were both expressed in the dorsal root ganglia, notochord, head mesenchyme, developing central nervous system (CNS), developing neck region (pharyngeal endoderm and the esophagus), mesonephric kidney, stomach, bulbus cortis, heart, lungs and endothelium of blood vessels. However, in the developing heart, lung, and stomach, Mmachc expression was cell type specific being limited to the cushions of the heart, right ventricle, and endoderm of the lung and stomach . This data suggest that although products of the two genes are proposed to interact, they may not do so in every single cell type.
Mtrr expression was analyzed in mice carrying a gene-trap allele that resulted in knock-in of LacZ into the locus. β-Galactosidase activity at E9.5 and E10.5 was used as a surrogate for gene expression. β-Galactosidase activity was found throughout the embryo with higher activity detected in the optic eminence, forebrain (telencephalon and diencephalon), midbrain, 2nd and 4th rhombomeres of the hindbrain, notochord and the neural tube. High β-galactosidase activity was also detected within the first brachial arch, splanchnic mesoderm, hindgut, and foregut. The observed sites of β-galactosidase activity at these stages suggest that Mtrr is broadly expressed during embryogenesis . At E14.5, Mtrr expression was also reported in the developing brain, in the upper and lower cortical plate, cerebral cortex subventricular zone and ventricular layer .
Visel et al., reported expression of Mtr at E14.5 in developing embryos [82,88]. Mtr expression was expressed in the forelimb, hindlimb, integumental system, and skin. Moderate Mtr expression was found in the nervous system, central nervous system, telencephalon, cerebral cortex, midbrain, inferior colliculus, spinal cord and tail. Weak Mtr expression was observed in the hippocampus, basal ganglia, neocortex, corpus striatum, choroid plexus, peripheral nervous system, cranial ganglion, dorsal root ganglion, eye, retina, alimentary system, tooth, renal-urinary system, reproductive system and genital tubercle. Thus, similar to Mtrr, Mtr was broadly expressed in developing embryos.
We also reported the expression pattern of Mmaa, Mmab and Mut at E10.5–E12.5 . At E10.5 we found higher expression of Mmaa, Mmab and Mut in the heart, branchial arches, and neural tube. By E11.5, we found co-expression of these genes in the dorsal root ganglion, developing heart, liver and tissue-specific expression pattern of these genes in head mesechyme and head endothelial vessels. However, at this stage, expression of Mmaa and Mmab was more robust than that of Mut. At E12.5, all three genes were expressed in head mesenchyme, blood vessels, heart and kidney. Mmaa and Mmab expression was tissue-specific in organs such as lung, gut, liver and urogenital sinus. In lung, Mmaa was most highly expressed in the endothelial cells of vessels and was not observed in the lung buds. In midgut, low levels of Mmab were detected in the mesenchyme but not in the gut endoderm. In the region of the developing urogenital sinus and rectum, we detected expression of Mmaa throughout of the urogenital sinus whereas Mmab was highly expressed in both the urogenital sinus and rectum, and Mut was also expressed in the urogenital sinus and rectum .
Although incomplete, the studies published to date suggest that genes associated with Cbl metabolism are not all ubiquitously expressed (Table 1). However, the expression pattern of these genes overlaps in the neural tube, dorsal root ganglion and heart, except for Mtr which was only analyzed at E14.5. These data provide evidence that Cbl may be necessary for normal neural tube, dorsal root ganglion, heart development and function during mouse organogenesis. These data also support a possible developmental origin for clinical features seen in Cbl deficiency patients such as neural tube defects, heart malformations and neurological disorders. It is clear that in addition to the expression pattern of the genes associated with cblF and cblJ, the expression pattern of all of these genes needs to be analyzed at similar stages in order to generate a complete atlas of where genes in the Cbl pathway are expressed during embryogenesis and the organs in which their Cbl metabolism may be critical for normal morphogenesis.
|Table 1. Summary of the main sites of expression of genes in vitamin B12 absorption during mouse embryogenesis from E9.5–E14.5. 1: only analyzed at E14.5; 2: only analyzed at E11.5; 3: only analyzed at E11.5, * ubiquitous expression; 4: analyzed at E9.5–E10.5 and E14.5, * ubiquitous expression at E9.5–E10.5; 5: only analyzed at E14.5; 6: analyzed at E10.5–E12.5; * ubiquitous expression at E10.5; 7: analyzed at E10.5–E12.5, * ubiquitous expression at E10.5; 8: analyzed at E10.5–E12.5, * ubiquitous expression at E12.5. Dorsal root ganglion (drg).|
|Endothelial vessel of head||+||+||+|
|Neural crest cells|
|Eye and ear|
|Intersomitic blood vessels||+||+|
5. Mouse Models
5.1. Cobalamin Absorption
Amnionless and cubilin help in absortion of Cbl from the blood stream into the epithelial cells of the distal ileum . The link between these proteins and a variety of developmental defects has been shown. The importance of this complex for normal fetal development was initially noted when antibodies that blocked their activities in yolk sac endoderm resulted in severe developmental abnormalities. Injection into rodents of antibodies raised against rat kidney, placenta and yolk sac resulted in decreased fetal weight, increased resorption rates, and increase incidence of cardiovascular defects, urogenital malformations, orofacial clefts, hydrocephalus, exencephaly and anencephaly. Later studies indicated that the antibodies recognized the Cbl intrisic-factor complex .
The human amnionless gene contains seven transcription start sites, two of which are positioned after exon 4 . Mutations in exons 1–4 of the human amnionless gene cause megaloblastic anemia, due to malabsorption of Cbl . Interestingly, mouse embryos lacking the amnionless gene product do not survive past the 10th day of gestation, have a poorly developed amnion, and an absence of trunk mesoderm . Since human patients have been reported with mutations in the first seven exons of amnionless, it is postulated that the C-terminus of the protein is required for proper embryonic development . This case is further supported by recent reports of patients with truncating mutations in Amn [94,95].
In mice, cubilin deficiency results in embryonic developmental defects that are smilar to those found in Amn embryos. Homozygous cubilin knockout embryos are developmentally delayed with absence of somite formation and abnormal endodermal function . Human cubilin is a large peripheral membrane protein that contains eight EGF-like and 27 CUB domains . Mutations in cubilin have been associated with impaired ligand binding of IF-Cbl, which results in megaloblastic anemia . Recently, a renal-biopsy specimen from a patient that was diagnosed with cubulin deficiency and a homozygous mutation in cubilin showed no immunologic reaction for cubulin and abnormal cytoplasmic and vesicular distribution of amnionless with no developmental defects , suggesting that cubilin may not be required for normal human development. In addition, although cubilin was initially described as a receptor for the IF-Cbl complex, it was also found to be involved in endocytosis of high-density lipoproteins and a number of other ligands . Therefore, the variety of roles played by cubilin in humans, and the difference in phenotypes of rodents and humans with cubilin deficiency, indicate that this protein may play differing roles between the two species.
5.2. Cobalamin and Folic Acid Pathways
Folic acid and Cbl deficiency is a risk factor for pathogenic conditions such as neural tube, limb, cardiac and jaw defects in fetal development. The importance of folic acid in preventing birth defects, and particularly neural tube defects during embryonic development has been widely reported and modelled in the mouse . In rat myocardium, Cbl deficiency during gestation and lactation results in postnatal growth retardation, myocardium hypertrophy (cardiomyocyte enlargement) lipid droplets, and decreases respiratory activity of complexes I and II with disturbed mitochondrial alignment, suggesting that Cbl deficiency may induce perinatal cardiomyopathies .
Folic acid and Cbl pathways are connected at the step where homocysteine is converted into methionine. In the cell, Cbl acts as a cofactor to MS (MTR), which catalyzes the re-methylation of homocysteine to methionine and the concurrent de-methylation of 5-methyltetrahydrofolate (5-Me-THF) to tetrahydrofolate (THF).
In mice, complete loss of Mthfd1, the gene which encodes the protein that catalyzes the formation and intercorvertion of folate-activated one carbon groups required for nucleotide biosynthesis and cellular methylation, results in early embryonic lethality during development. However, mice heterozygous for a Mthfd1 null allele were viable and exhibited impaired cellular methylation with a 50% decrease of MTHFD1 proteins levels. In addition, maternal Mthfd1 disruption contributed to abnormal embryonic development with growth retriction, irregular neuroepithelial organization, and torqued body symmetry at E11.5 without any neural tubes defects .
Homozygosity for loss of function mutations in either Mtr or Mtrr—the genes mutated in cblG and cblE patients, respectively—is embryonic lethal in mice [84,104]. Mouse embryos with MS deficiency can implant but die soon after. Whereas mice heterozygous for the Ms null allele have a 60% reduction in MS activity, are viable and survive to adulthood ; hypomorphs of Mtrr exhibit metabolic derangement of methionine and folate metabolism with increased plasma homocyst(e)ine, increased tissue methyltetrahydrofolate, and decreased plasma methionine with no change in AdoMet/AdoHcy ratio in most tissues . In E14.5, embryos Mtrr deficiency results in congenital heart defects such as myocardial hypoplasia and higher incidence of ventricular septal defects (VSD) and reduced embryonic length. In mothers, Mtrr deficiency results in adverse reproductive outcomes with more resorptions, more delayed embryos and smaller placenta .
Homozygosity for loss of function mutations in 5,10-methylenetetrahydrofolate reductase (Mthfr) results in reduced survival at two weeks of age with a series of neurological complications: motor and gait abnormalities or delayed development , cerebellar abnormalities with effects on granule cell development, neuronal organisation , and neurobiological changes in the hippocampus , suggesting that Mthfr is important for proper neuronal development in mice. Similar to humans, maternal Mthfr deficiency and low dietary folate in mice lead to adverse reproductive outcomes such as increased incidence of pregnancy loss, fetal growth retardation and congenital heart defects .
5.3. Cobalamin and Methylmalonyl-CoA Mutase (MCM)
Mouse models with mutations in Mmaa, Mmab, Mmachc, Mmadhc or Lmbrd1 have yet to be described. Although, MCM is not required during embryogenesis, targeted deletion of Mut results in perinatal lethality . Mutations affecting MCM, which participates in the catabolism of odd-chain fatty acids, some branched amino acids and cholesterol, is the mouse model that has been widely used to study defects in one-carbon metabolism. Mouse pups with no functional copy of the Mut gene (Mut−/−) are normal at birth but show abnormal breathing, reduced movement, reduced suckling, and die within 24 h of birth  with elevated levels of methylmalonic and methylcitric acids. However, when the Mut mutation was placed on a mixed Fbv/n genetic background, a number of Mut−/− mice survived and exhibited large mitochondria in kidney, liver and pancreas, a phenotype that was later confirmed in human liver samples from mut patients .
Neonatal lethality of Mut−−/−− mice was rescued by virus-mediated gene therapy, through intrahepatic injections of adenovirus carrying the Mut gene (Ad-Mut-GFP), (rAAV8), (rAAV9) [112,113,114]. Survival of homozygous mutant pups was monitored for longer than one year, and although expression of the transgene decreased over time, the mice remained indistinguishable from wild type littermates in size and activity levels. Treated Mut−−/−− mice lived beyond one year of age, had improved growth, lower plasma methylmalonic acid levels, and an increased capacity to oxidize propionate in vivo , thus illustrating the power of mouse models and the need for additional models in this system.
Transgenic mice carrying an intact human MUT locus also have been produced. Transgenic mice were crossed with heterozygous knockout Mut mice to generate mice hemizygous for the human transgene on a homozygous knockout background. Partial rescue of the uniformly neonatal lethality in homozygous knockout mice was observed. These rescued mice were significantly smaller than mice with the wild type Mut gene and exhibited elevated methylmalonic acid levels in urine, plasma, kidney, liver and brain tissue. The human transgene was expressed at higher levels in the kidney followed closely by brain and liver as compared to the wild type mice , confirming that the human and mouse proteins are almost completely interchangeable.
In addition, a mouse model that contains a human methylmalonyl-CoA mutase locus carrying a stop codon mutation identified in a patient with Mut MMA was generated. The transgene was found to be intact in the mouse model, with seven copies integrated at a single site in chromosome 3. The phenotype of the hemizygous mouse was unchanged until crossed against a methylmalonyl-CoA mutase knockout mouse. Pups with no endogenous mouse methylmalonyl-CoA mutase and one copy of the transgene became ill and died within 24 h. This severe phenotype was partially rescued by the addition of a transgene carrying two copies of the normal human methylmalonyl-CoA mutase locus . In addition, the “humanized” mice mimicked the key features of the human MMA disorder allowing the authors to use genetic therapies such as fetal progenitor cell transplantation in the liver, bone marrow and spleen to treat this disorder .
Finally, administration of folinic acid and Cbl together has been shown to be protective against a number of malformations including neural tube defects, branchial arch abnormalities and cardiac defects caused by ethanol exposure during mouse pregnancies, whereas, Cbl or folinic acid alone did not have any significant protective effect . Recently, Cbl was shown to support palate fusion in the presence of concentrations of dexamethasone, which normally impaired fusion of murine palates in organ culture . In vivo, Cbl in the presence of dexamethasone restored proliferation of the mesenchymal cells of the palate via increased expression of a growth factor—Fgf10—which is normally involved in craniofacial development , and thus, suggesting that Cbl may indirectly regulate the levels of growth factors essential for normal organogenesis.
The genes involved in the vitamin B12 metabolism are not ubiquitously expressed during embryogenesis suggesting that the proteins encoded by these genes may not interact throughout organogenesis. These findings lead us to postulate that a subset of the genes involved in vitamin B12 metabolism may have “moonlighting” functions. Thus, it is possible that developmental phenotypes in patients with mutations in these genes are due to (a) abnormal vitamin B12 metabolism and/or (b) some other unknown requirement for the proteins encoded by genes in the vitamin B12 pathway. In the future, mouse models of Mmachc, Mmadhc, Lmbrd1 and Abcd4 deficiency may shed insight into the roles of these proteins during development and explain the etiology of developmental phenotypes in a subset of patients. Proper understanding of the role of Cbl in embryonic development will also determine whether Cbl supplementation should be used in conjunction with folic acid supplementation in order to further prevent the occurrence of neural tube and heart birth defects during pregnancy.
We thank David Watkins for providing Figure 1 and for his helpful comments. We thank members of the Jerome-Majewska laboratory for their reading the manuscript.
Conflicts of Interest
The authors declare no conflicts of interest.
- MRC Vitamin Study Research Group. Prevention of neural tube defects: Results of the medical research council vitamin study. Lancet 1991, 338, 131–137, doi:10.1016/0140-6736(91)90133-A.
- Czeizel, A.E.; Dudas, I. Prevention of the first occurrence of neural-tube defects by periconceptional vitamin supplementation. N. Engl. J. Med. 1992, 327, 1832–1835, doi:10.1056/NEJM199212243272602.
- Heseker, H.B.; Mason, J.B.; Selhub, J.; Rosenberg, I.H.; Jacques, P.F. Not all cases of neural-tube defect can be prevented by increasing the intake of folic acid. Br. J. Nutr. 2009, 102, 173–180, doi:10.1017/S0007114508149200.
- Black, M.M. Effects of vitamin B12 and folate deficiency on brain development in children. Food Nutr. Bull. 2008, 29, S126–S131.
- Gadhok, A.K.; Sinha, M.; Khunteta, R.; Vardey, S.K.; Upadhyaya, C.; Sharma, T.K.; Jha, M. Serum homocysteine level and its association with folic acid and vitamin B12 in the third trimester of pregnancies complicated with intrauterine growth restriction. Clin. Lab. 2011, 57, 933–938.
- Hozyasz, K.K.; Oltarzewski, M.; Lugowska, I.; Szymanski, M.; Surowiec, Z. Whole blood propionylcarnitine in newborns with orofacial cleft. Matern. Child Nutr. 2011, 7, 100–103, doi:10.1111/j.1740-8709.2010.00240.x.
- Muthayya, S.; Kurpad, A.V.; Duggan, C.P.; Bosch, R.J.; Dwarkanath, P.; Mhaskar, A.; Mhaskar, R.; Thomas, A.; Vaz, M.; Bhat, S.; et al. Low maternal vitamin B12 status is associated with intrauterine growth retardation in urban South Indians. Eur. J. Clin. Nutr. 2006, 60, 791–801, doi:10.1038/sj.ejcn.1602383.
- Froese, D.S.; Healy, S.; McDonald, M.; Kochan, G.; Oppermann, U.; Niesen, F.H.; Gravel, R.A. Thermolability of mutant MMACHC protein in the vitamin B12-responsive cblC disorder. Mol. Genet. Metab. 2010, 100, 29–36, doi:10.1016/j.ymgme.2010.02.005.
- Fowler, B. Genetic defects of folate and cobalamin metabolism. Eur. J. Pediatr. 1998, 157, S60–S66, doi:10.1007/PL00014306.
- Fyfe, J.C.; Madsen, M.; Hojrup, P.; Christensen, E.I.; Tanner, S.M.; de la Chapelle, A.; He, Q.; Moestrup, S.K. The functional cobalamin (vitamin B12)-intrinsic factor receptor is a novel complex of cubilin and amnionless. Blood 2004, 103, 1573–1579, doi:10.1182/blood-2003-08-2852.
- Moestrup, S.K.; Kozyraki, R.; Kristiansen, M.; Kaysen, J.H.; Rasmussen, H.H.; Brault, D.; Pontillon, F.; Goda, F.O.; Christensen, E.I.; Hammond, T.G.; et al. The intrinsic factor-vitamin B12 receptor and target of teratogenic antibodies is a megalin-binding peripheral membrane protein with homology to developmental proteins. J. Biol. Chem. 1998, 273, 5235–5242, doi:10.1074/jbc.273.9.5235.
- Quadros, E.V.; Sequeira, J.M. Cellular uptake of cobalamin: Transcobalamin and the TCblR/CD320 receptor. Biochimie 2013, 95, 1008–1018, doi:10.1016/j.biochi.2013.02.004.
- Youngdahl-Turner, P.; Rosenberg, L.E.; Allen, R.H. Binding and uptake of transcobalamin II by human fibroblasts. J. Clin. Investig. 1978, 61, 133–141, doi:10.1172/JCI108911.
- Youngdahl-Turner, P.; Mellman, I.S.; Allen, R.H.; Rosenberg, L.E. Protein mediated vitamin uptake. Exp. Cell. Res. 1979, 118, 127–134, doi:10.1016/0014-4827(79)90590-1.
- Laframboise, R.; Cooper, B.A.; Rosenblatt, D.S. Malabsorption of vitamin B12 from the intestine in a child with cblF disease: Evidence for lysosomal-mediated absorption. Blood 1992, 80, 291–292.
- Miousse, I.R.; Watkins, D.; Rosenblatt, D.S. Novel splice site mutations and a large deletion in three patients with the cblF inborn error of vitamin B12 metabolism. Mol. Genet. Metab. 2011, 102, 505–507, doi:10.1016/j.ymgme.2011.01.002.
- Oladipo, O.; Rosenblatt, D.S.; Watkins, D.; Miousse, I.R.; Sprietsma, L.; Dietzen, D.J.; Shinawi, M. Cobalamin F disease detected by newborn screening and follow-up on a 14-year-old patient. Pediatrics 2011, 128, 2010–3518.
- Rutsch, F.; Gailus, S.; Miousse, I.R.; Suormala, T.; Sagne, C.; Toliat, M.R.; Nurnberg, G.; Wittkampf, T.; Buers, I.; Sharifi, A.; et al. Identification of a putative lysosomal cobalamin exporter altered in the cblF defect of vitamin B12 metabolism. Nat. Genet. 2009, 41, 234–239, doi:10.1038/ng.294.
- Shih, V.E.; Axel, S.M.; Tewksbury, J.C.; Watkins, D.; Cooper, B.A.; Rosenblatt, D.S. Defective lysosomal release of vitamin B12 (cb1F): A hereditary cobalamin metabolic disorder associated with sudden death. Am. J. Med. Genet. 1989, 33, 555–563, doi:10.1002/ajmg.1320330431.
- Vassiliadis, A.; Rosenblatt, D.S.; Cooper, B.A.; Bergeron, J.J. Lysosomal cobalamin accumulation in fibroblasts from a patient with an inborn error of cobalamin metabolism (cblF complementation group): Visualization by electron microscope radioautography. Exp. Cell. Res. 1991, 195, 295–302, doi:10.1016/0014-4827(91)90376-6.
- Waggoner, D.J.; Ueda, K.; Mantia, C.; Dowton, S.B. Methylmalonic aciduria (cblF): Case report and response to therapy. Am. J. Med. Genet. 1998, 79, 373–375, doi:10.1002/(SICI)1096-8628(19981012)79:5<373::AID-AJMG8>3.0.CO;2-K.
- Watkins, D.; Rosenblatt, D.S. Failure of lysosomal release of vitamin B12: A new complementation group causing methylmalonic aciduria (cblF). Am. J. Hum. Genet. 1986, 39, 404–408.
- Coelho, D.; Kim, J.C.; Miousse, I.R.; Fung, S.; du Moulin, M.; Buers, I.; Suormala, T.; Burda, P.; Frapolli, M.; Stucki, M.; et al. Mutations in ABCD4 cause a new inborn error of vitamin B12 metabolism. Nat. Genet. 2012, 44, 1152–1155, doi:10.1038/ng.2386.
- Lerner-Ellis, J.P.; Tirone, J.C.; Pawelek, P.D.; Dore, C.; Atkinson, J.L.; Watkins, D.; Morel, C.F.; Fujiwara, T.M.; Moras, E.; Hosack, A.R.; et al. Identification of the gene responsible for methylmalonic aciduria and homocystinuria, cblC type. Nat. Genet. 2006, 38, 93–100, doi:10.1038/ng1683.
- Kim, J.; Gherasim, C.; Banerjee, R. Decyanation of vitamin B12 by a trafficking chaperone. Proc. Natl. Acad. Sci. USA 2008, 105, 14551–14554, doi:10.1073/pnas.0805989105.
- Hannibal, L.; Kim, J.; Brasch, N.E.; Wang, S.; Rosenblatt, D.S.; Banerjee, R.; Jacobsen, D.W. Processing of alkylcobalamins in mammalian cells: A role for the MMACHC (cblC) gene product. Mol. Genet. Metab. 2009, 97, 260–266, doi:10.1016/j.ymgme.2009.04.005.
- Plesa, M.; Kim, J.; Paquette, S.G.; Gagnon, H.; Ng-Thow-Hing, C.; Gibbs, B.F.; Hancock, M.A.; Rosenblatt, D.S.; Coulton, J.W. Interaction between MMACHC and MMADHC, two human proteins participating in intracellular vitamin B12 metabolism. Mol. Genet. Metab. 2011, 102, 139–148, doi:10.1016/j.ymgme.2010.10.011.
- Takahashi-Iniguez, T.; Garcia-Arellano, H.; Trujillo-Roldan, M.A.; Flores, M.E. Protection and reactivation of human methylmalonyl-CoA mutase by MMAA protein. Biochem. Biophys. Res. Commun. 2011, 404, 443–447, doi:10.1016/j.bbrc.2010.11.141.
- Takahashi-Iniguez, T.; Garcia-Hernandez, E.; Arreguin-Espinosa, R.; Flores, M.E. Role of vitamin B12 on methylmalonyl-CoA mutase activity. J. Zhejiang Univ. Sci. B 2012, 13, 423–437, doi:10.1631/jzus.B1100329.
- Dobson, C.M.; Wai, T.; Leclerc, D.; Kadir, H.; Narang, M.; Lerner-Ellis, J.P.; Hudson, T.J.; Rosenblatt, D.S.; Gravel, R.A. Identification of the gene responsible for the cblB complementation group of vitamin B12-dependent methylmalonic aciduria. Hum. Mol. Genet. 2002, 11, 3361–3369, doi:10.1093/hmg/11.26.3361.
- Leal, N.A.; Park, S.D.; Kima, P.E.; Bobik, T.A. Identification of the human and bovine ATP:Cob(I)alamin adenosyltransferase cDNAs based on complementation of a bacterial mutant. J. Biol. Chem. 2003, 278, 9227–9234.
- Yamanishi, M.; Vlasie, M.; Banerjee, R. Adenosyltransferase: An enzyme and an escort for coenzyme B12? Trends Biochem. Sci. 2005, 30, 304–308, doi:10.1016/j.tibs.2005.04.008.
- Gaber, K.R.; Farag, M.K.; Soliman, S.E.; El-Bassyouni, H.T.; El-Kamah, G. Maternal vitamin B12 and the risk of fetal neural tube defects in Egyptian patients. Clin. Lab. 2007, 53, 69–75.
- Molloy, A.M.; Kirke, P.N.; Troendle, J.F.; Burke, H.; Sutton, M.; Brody, L.C.; Scott, J.M.; Mills, J.L. Maternal vitamin B12 status and risk of neural tube defects in a population with high neural tube defect prevalence and no folic Acid fortification. Pediatrics 2009, 123, 917–923, doi:10.1542/peds.2008-1173.
- Ray, J.G.; Wyatt, P.R.; Thompson, M.D.; Vermeulen, M.J.; Meier, C.; Wong, P.Y.; Farrell, S.A.; Cole, D.E. Vitamin B12 and the risk of neural tube defects in a folic-acid-fortified population. Epidemiology 2007, 18, 362–366, doi:10.1097/01.ede.0000257063.77411.e9.
- Thompson, M.D.; Cole, D.E.; Ray, J.G. Vitamin B-12 and neural tube defects: The Canadian experience. Am. J. Clin. Nutr. 2009, 89, 697S–701S, doi:10.3945/ajcn.2008.26947B.
- Zhang, T.; Xin, R.; Gu, X.; Wang, F.; Pei, L.; Lin, L.; Chen, G.; Wu, J.; Zheng, X. Maternal serum vitamin B12, folate and homocysteine and the risk of neural tube defects in the offspring in a high-risk area of China. Public Health Nutr. 2009, 12, 680–686, doi:10.1017/S1368980008002735.
- Ceyhan, S.T.; Beyan, C.; Atay, V.; Yaman, H.; Alanbay, I.; Kaptan, K.; Baser, I. Serum vitamin B12 and homocysteine levels in pregnant women with neural tube defect. Gynecol. Endocrinol. 2010, 26, 578–581, doi:10.3109/09513591003632183.
- Economides, D.L.; Ferguson, J.; Mackenzie, I.Z.; Darley, J.; Ware, II; Holmes-Siedle, M. Folate and vitamin B12 concentrations in maternal and fetal blood, and amniotic fluid in second trimester pregnancies complicated by neural tube defects. Br. J. Obstet. Gynaecol. 1992, 99, 23–25.
- Mills, J.L.; Tuomilehto, J.; Yu, K.F.; Colman, N.; Blaner, W.S.; Koskela, P.; Rundle, W.E.; Forman, M.; Toivanen, L.; Rhoads, G.G. Maternal vitamin levels during pregnancies producing infants with neural tube defects. J. Pediatr. 1992, 120, 863–871, doi:10.1016/S0022-3476(05)81951-1.
- Molloy, A.M.; Kirke, P.; Hillary, I.; Weir, D.G.; Scott, J.M. Maternal serum folate and vitamin B12 concentrations in pregnancies associated with neural tube defects. Arch. Dis. Child. 1985, 60, 660–665, doi:10.1136/adc.60.7.660.
- Schorah, C.J.; Smithells, R.W.; Scott, J. Vitamin B12 and anencephaly. Lancet 1980, 315, 880, doi:10.1016/S0140-6736(80)91381-1.
- Stoll, C.; Dott, B.; Alembik, Y.; Koehl, C. Maternal trace elements, vitamin B12, vitamin A, folic acid, and fetal malformations. Reprod. Toxicol. 1999, 13, 53–57, doi:10.1016/S0890-6238(98)00058-6.
- Suarez, L.; Hendricks, K.; Felkner, M.; Gunter, E. Maternal serum B12 levels and risk for neural tube defects in a Texas-Mexico border population. Ann. Epidemiol. 2003, 13, 81–88, doi:10.1016/S1047-2797(02)00267-3.
- Thorand, B.; Pietrzik, K.; Prinz-Langenohl, R.; Hages, M.; Holzgreve, W. Maternal and fetal serum and red blood cell folate and vitamin B12 concentrations in pregnancies affected by neural tube defects. Z. Geburtshilfe Neonatol. 1996, 200, 176–180.
- Van der Put, N.M.; Thomas, C.M.; Eskes, T.K.; Trijbels, F.J.; Steegers-Theunissen, R.P.; Mariman, E.C.; de Graaf-Hess, A.; Smeitink, J.A.; Blom, H.J. Altered folate and vitamin B12 metabolism in families with spina bifida offspring. QJM 1997, 90, 505–510, doi:10.1093/qjmed/90.8.505.
- Wild, J.; Schorah, C.J.; Sheldon, T.A.; Smithells, R.W. Investigation of factors influencing folate status in women who have had a neural tube defect-affected infant. Br. J. Obstet. Gynaecol. 1993, 100, 546–549, doi:10.1111/j.1471-0528.1993.tb15306.x.
- Ray, J.G.; Blom, H.J. Vitamin B12 insufficiency and the risk of fetal neural tube defects. QJM 2003, 96, 289–295, doi:10.1093/qjmed/hcg043.
- Brouns, R.; Ursem, N.; Lindemans, J.; Hop, W.; Pluijm, S.; Steegers, E.; Steegers-Theunissen, R. Polymorphisms in genes related to folate and cobalamin metabolism and the associations with complex birth defects. Prenat. Diagn. 2008, 28, 485–493, doi:10.1002/pd.2006.
- Dawson, E.B.; Evans, D.R.; Harris, W.A.; van Hook, J.W. Amniotic fluid B12, calcium, and lead levels associated with neural tube defects. Am. J. Perinatol. 1999, 16, 373–378, doi:10.1055/s-2007-993887.
- Dawson, E.B.; Evans, D.R.; van Hook, J.W. Amniotic fluid B12 and folate levels associated with neural tube defects. Am. J. Perinatol. 1998, 15, 511–514, doi:10.1055/s-2007-993975.
- Gardiki-Kouidou, P.; Seller, M.J. Amniotic fluid folate, vitamin B12 and transcobalamins in neural tube defects. Clin. Genet. 1988, 33, 441–448, doi:10.1111/j.1399-0004.1988.tb03478.x.
- Steegers-Theunissen, R.P.; Boers, G.H.; Blom, H.J.; Nijhuis, J.G.; Thomas, C.M.; Borm, G.F.; Eskes, T.K. Neural tube defects and elevated homocysteine levels in amniotic fluid. Am. J. Obstet. Gynecol. 1995, 172, 1436–1441, doi:10.1016/0002-9378(95)90474-3.
- Weekes, E.W.; Tamura, T.; Davis, R.O.; Birch, R.; Vaughn, W.H.; Franklin, J.C.; Barganier, C.; Cosper, P.; Finley, S.C.; Finley, W.H. Nutrient levels in amniotic fluid from women with normal and neural tube defect pregnancies. Biol. Neonate 1992, 61, 226–231, doi:10.1159/000243747.
- Magnus, P.; Magnus, E.M.; Berg, K. Increased levels of apo-transcobalamins I and II in amniotic fluid from pregnant women with previous neural tube defect offspring. Clin. Genet. 1986, 30, 167–172.
- Magnus, P.; Magnus, E.M.; Berg, K. Transcobalamins in the etiology of neural tube defects. Clin. Genet. 1991, 39, 309–310, doi:10.1111/j.1399-0004.1991.tb03032.x.
- Lindgren, A.; Kilander, A.; Bagge, E.; Nexo, E. Holotranscobalamin—A sensitive marker of cobalamin malabsorption. Eur. J. Clin. Investig. 1999, 29, 321–329.
- Tisman, G.; Vu, T.; Amin, J.; Luszko, G.; Brenner, M.; Ramos, M.; Flener, V.; Cordts, V.; Bateman, R.; Malkin, S.; et al. Measurement of red blood cell-vitamin B12: A study of the correlation between intracellular B12 content and concentrations of plasma holotranscobalamin II. Am. J. Hematol. 1993, 43, 226–229, doi:10.1002/ajh.2830430313.
- Al Aisari, F.; Al-Hashmi, H.; Mula-Abed, W.A. Comparison between serum holotranscobalamin and total vitamin B12 as indicators of vitamin B12 status. Oman Med. J. 2010, 25, 9–12.
- Van Rooij, I.A.; Swinkels, D.W.; Blom, H.J.; Merkus, H.M.; Steegers-Theunissen, R.P. Vitamin and homocysteine status of mothers and infants and the risk of nonsyndromic orofacial clefts. Am. J. Obstet. Gynecol. 2003, 189, 1155–1160, doi:10.1067/S0002-9378(03)00592-1.
- Bille, C.; Olsen, J.; Vach, W.; Knudsen, V.K.; Olsen, S.F.; Rasmussen, K.; Murray, J.C.; Andersen, A.M.; Christensen, K. Oral clefts and life style factors—A case-cohort study based on prospective Danish data. Eur. J. Epidemiol. 2007, 22, 173–181, doi:10.1007/s10654-006-9099-5.
- Krapels, I.P.; van Rooij, I.A.; Ocke, M.C.; van Cleef, B.A.; Kuijpers-Jagtman, A.M.; Steegers-Theunissen, R.P. Maternal dietary B vitamin intake, other than folate, and the association with orofacial cleft in the offspring. Eur. J. Nutr. 2004, 43, 7–14, doi:10.1007/s00394-004-0433-y.
- Franke, B.; Vermeulen, S.H.; Steegers-Theunissen, R.P.; Coenen, M.J.; Schijvenaars, M.M.; Scheffer, H.; den Heijer, M.; Blom, H.J. An association study of 45 folate-related genes in spina bifida: Involvement of cubilin (CUBN) and tRNA aspartic acid methyltransferase 1 (TRDMT1). Birth Defects Res. 2009, 85, 216–226, doi:10.1002/bdra.20556.
- Gos, M.; Sliwerska, E.; Szpecht-Potocka, A. Mutation incidence in folate metabolism genes and regulatory genes in Polish families with neural tube defects. J. Appl. Genet. 2004, 45, 363–368.
- Ouyang, S.; Li, Y.; Liu, Z.; Chang, H.; Wu, J. Association between MTR A2756G and MTRR A66G polymorphisms and maternal risk for neural tube defects: A meta-analysis. Gene 2013, 515, 308–312, doi:10.1016/j.gene.2012.11.070.
- Pietrzyk, J.J.; Bik-Multanowski, M.; Sanak, M.; Twardowska, M. Polymorphisms of the 5,10-methylenetetrahydrofolate and the methionine synthase reductase genes as independent risk factors for spina bifida. J. Appl. Genet. 2003, 44, 111–113.
- Van der Linden, I.J.; den Heijer, M.; Afman, L.A.; Gellekink, H.; Vermeulen, S.H.; Kluijtmans, L.A.; Blom, H.J. The methionine synthase reductase 66A>G polymorphism is a maternal risk factor for spina bifida. J. Mol. Med. 2006, 84, 1047–1054, doi:10.1007/s00109-006-0093-x.
- Wilson, A.; Platt, R.; Wu, Q.; Leclerc, D.; Christensen, B.; Yang, H.; Gravel, R.A.; Rozen, R. A common variant in methionine synthase reductase combined with low cobalamin (vitamin B12) increases risk for spina bifida. Mol. Genet. Metab. 1999, 67, 317–323, doi:10.1006/mgme.1999.2879.
- Zhu, H.; Wicker, N.J.; Shaw, G.M.; Lammer, E.J.; Hendricks, K.; Suarez, L.; Canfield, M.; Finnell, R.H. Homocysteine remethylation enzyme polymorphisms and increased risks for neural tube defects. Mol. Genet. Metab. 2003, 78, 216–221, doi:10.1016/S1096-7192(03)00008-8.
- Doolin, M.T.; Barbaux, S.; McDonnell, M.; Hoess, K.; Whitehead, A.S.; Mitchell, L.E. Maternal genetic effects, exerted by genes involved in homocysteine remethylation, influence the risk of spina bifida. Am. J. Hum. Genet. 2002, 71, 1222–1226, doi:10.1086/344209.
- Relton, C.L.; Wilding, C.S.; Pearce, M.S.; Laffling, A.J.; Jonas, P.A.; Lynch, S.A.; Tawn, E.J.; Burn, J. Gene-gene interaction in folate-related genes and risk of neural tube defects in a UK population. J. Med. Genet. 2004, 41, 256–260, doi:10.1136/jmg.2003.010694.
- Brandalize, A.P.; Bandinelli, E.; Borba, J.B.; Felix, T.M.; Roisenberg, I.; Schuler-Faccini, L. Polymorphisms in genes MTHFR, MTR and MTRR are not risk factors for cleft lip/palate in South Brazil. Braz. J. Med. Biol. Res. 2007, 40, 787–791, doi:10.1590/S0100-879X2006005000112.
- Candito, M.; Rivet, R.; Herbeth, B.; Boisson, C.; Rudigoz, R.C.; Luton, D.; Journel, H.; Oury, J.F.; Roux, F.; Saura, R.; et al. Nutritional and genetic determinants of vitamin B and homocysteine metabolisms in neural tube defects: A multicenter case-control study. Am. J. Med. Genet. 2008, 1, 1128–1133.
- Ouyang, S.; Liu, Z.; Li, Y.; Wu, J. Meta-analyses on the association of MTR A2756G and MTRR A66G polymorphisms with neural tube defect risks in Caucasian children. J. Matern. Fetal Neonatal Med. 2013, 26, 1166–1170, doi:10.3109/14767058.2013.777699.
- Relton, C.L.; Wilding, C.S.; Laffling, A.J.; Jonas, P.A.; Burgess, T.; Binks, K.; Tawn, E.J.; Burn, J. Low erythrocyte folate status and polymorphic variation in folate-related genes are associated with risk of neural tube defect pregnancy. Mol. Genet. Metab. 2004, 81, 273–281, doi:10.1016/j.ymgme.2003.12.010.
- Van Beynum, I.M.; Kouwenberg, M.; Kapusta, L.; den Heijer, M.; van der Linden, I.J.; Daniels, O.; Blom, H.J. MTRR 66A>G polymorphism in relation to congenital heart defects. Clin. Chem. Lab. Med. 2006, 44, 1317–1323.
- Mostowska, A.; Hozyasz, K.K.; Jagodzinski, P.P. Maternal MTR genotype contributes to the risk of non-syndromic cleft lip and palate in the Polish population. Clin. Genet. 2006, 69, 512–517.
- Al Farra, H.Y. Methionine synthase polymorphisms (MTR 2756A>G and MTR 2758C>G) frequencies and distribution in the Jordanian population and their correlation with neural tube defects in the population of the northern part of Jordan. Indian J. Hum. Genet. 2010, 16, 138–143, doi:10.4103/0971-6866.73405.
- Gueant-Rodriguez, R.M.; Rendeli, C.; Namour, B.; Venuti, L.; Romano, A.; Anello, G.; Bosco, P.; Debard, R.; Gerard, P.; Viola, M.; et al. Transcobalamin and methionine synthase reductase mutated polymorphisms aggravate the risk of neural tube defects in humans. Neurosci. Lett. 2003, 344, 189–192, doi:10.1016/S0304-3940(03)00468-3.
- Pangilinan, F.; Mitchell, A.; VanderMeer, J.; Molloy, A.M.; Troendle, J.; Conley, M.; Kirke, P.N.; Sutton, M.; Sequeira, J.M.; Quadros, E.V.; et al. Transcobalamin II receptor polymorphisms are associated with increased risk for neural tube defects. J. Med. Genet. 2010, 47, 677–685, doi:10.1136/jmg.2009.073775.
- Martinelli, M.; Scapoli, L.; Palmieri, A.; Pezzetti, F.; Baciliero, U.; Padula, E.; Carinci, P.; Morselli, P.G.; Carinci, F. Study of four genes belonging to the folate pathway: Transcobalamin 2 is involved in the onset of non-syndromic cleft lip with or without cleft palate. Hum. Mutat. 2006, 27, 294.
- Cherukad, J.; Wainwright, V.; Watson, E.D. Spatial and temporal expression of folate-related transporters and metabolic enzymes during mouse placental development. Placenta 2012, 33, 440–448.
- Diez-Roux, G.; Banfi, S.; Sultan, M.; Geffers, L.; Anand, S.; Rozado, D.; Magen, A.; Canidio, E.; Pagani, M.; Peluso, I.; et al. A high-resolution anatomical atlas of the transcriptome in the mouse embryo. PLoS Biol. 2011, 9, e1000582.
- Elmore, C.L.; Wu, X.; Leclerc, D.; Watson, E.D.; Bottiglieri, T.; Krupenko, N.I.; Krupenko, S.A.; Cross, J.C.; Rozen, R.; Gravel, R.A.; et al. Metabolic derangement of methionine and folate metabolism in mice deficient in methionine synthase reductase. Mol. Genet. Metab. 2007, 91, 85–97.
- Moreno-Garcia, M.A.; Rosenblatt, D.S.; Jerome-Majewska, L.A. The methylmalonic aciduria related genes, Mmaa, Mmab, and Mut, are broadly expressed in placental and embryonic tissues during mouse organogenesis. Mol. Genet. Metab. 2012, 107, 368–374.
- Pupavac, M.; Garcia, M.A.; Rosenblatt, D.S.; Jerome-Majewska, L.A. Expression of Mmachc and Mmadhc during mouse organogenesis. Mol. Genet. Metab. 2011, 103, 401–405, doi:10.1016/j.ymgme.2011.04.004.
- Sansom, S.N.; Griffiths, D.S.; Faedo, A.; Kleinjan, D.J.; Ruan, Y.; Smith, J.; van Heyningen, V.; Rubenstein, J.L.; Livesey, F.J. The level of the transcription factor Pax6 is essential for controlling the balance between neural stem cell self-renewal and neurogenesis. PLoS Genet. 2009, 5, e1000511, doi:10.1371/journal.pgen.1000511.
- Visel, A.; Thaller, C.; Eichele, G. GenePaint.org: An atlas of gene expression patterns in the mouse embryo. Nucleic Acids Res. 2004, 32, D552–D556, doi:10.1093/nar/gkh029.
- Li, F.; Watkins, D.; Rosenblatt, D.S. Vitamin B(12) and birth defects. Mol. Genet. Metab. 2009, 98, 166–172, doi:10.1016/j.ymgme.2009.06.004.
- Seetharam, B.; Christensen, E.I.; Moestrup, S.K.; Hammond, T.G.; Verroust, P.J. Identification of rat yolk sac target protein of teratogenic antibodies, gp280, as intrinsic factor-cobalamin receptor. J. Clin. Investig. 1997, 99, 2317–2322, doi:10.1172/JCI119411.
- Tanner, S.M.; Aminoff, M.; Wright, F.A.; Liyanarachchi, S.; Kuronen, M.; Saarinen, A.; Massika, O.; Mandel, H.; Broch, H.; de la Chapelle, A. Amnionless, essential for mouse gastrulation, is mutated in recessive hereditary megaloblastic anemia. Nat. Genet. 2003, 33, 426–429, doi:10.1038/ng1098.
- Wang, X.; Bornslaeger, E.A.; Haub, O.; Tomihara-Newberger, C.; Lonberg, N.; Dinulos, M.B.; Disteche, C.M.; Copeland, N.; Gilbert, D.J.; Jenkins, N.A.; et al. A candidate gene for the amnionless gastrulation stage mouse mutation encodes a TRAF-related protein. Dev. Biol. 1996, 177, 274–290, doi:10.1006/dbio.1996.0162.
- Tomihara-Newberger, C.; Haub, O.; Lee, H.G.; Soares, V.; Manova, K.; Lacy, E. The amn gene product is required in extraembryonic tissues for the generation of middle primitive streak derivatives. Dev. Biol. 1998, 204, 34–54, doi:10.1006/dbio.1998.9034.
- Densupsoontorn, N.; Sanpakit, K.; Vijarnsorn, C.; Pattaragarn, A.; Kangwanpornsiri, C.; Jatutipsompol, C.; Tirapongporn, H.; Jirapinyo, P.; Shah, N.P.; Sturm, A.C.; et al. Imerslund-grasbeck syndrome: New mutation in amnionless. Pediatr. Int. 2012, 54, e19–e21, doi:10.1111/j.1442-200X.2011.03482.x.
- Namour, F.; Dobrovoljski, G.; Chery, C.; Audonnet, S.; Feillet, F.; Sperl, W.; Gueant, J.L. Luminal expression of cubilin is impaired in Imerslund-Grasbeck syndrome with compound AMN mutations in intron 3 and exon 7. Haematologica 2011, 96, 1715–1719, doi:10.3324/haematol.2011.043984.
- Smith, B.T.; Mussell, J.C.; Fleming, P.A.; Barth, J.L.; Spyropoulos, D.D.; Cooley, M.A.; Drake, C.J.; Argraves, W.S. Targeted disruption of cubilin reveals essential developmental roles in the structure and function of endoderm and in somite formation. BMC Dev. Biol. 2006, 6, 30, doi:10.1186/1471-213X-6-30.
- Kozyraki, R.; Kristiansen, M.; Silahtaroglu, A.; Hansen, C.; Jacobsen, C.; Tommerup, N.; Verroust, P.J.; Moestrup, S.K. The human intrinsic factor-vitamin B12 receptor, cubilin: Molecular characterization and chromosomal mapping of the gene to 10 p within the autosomal recessive megaloblastic anemia (MGA1) region. Blood 1998, 91, 3593–3600.
- Kristiansen, M.; Aminoff, M.; Jacobsen, C.; de La Chapelle, A.; Krahe, R.; Verroust, P.J.; Moestrup, S.K. Cubilin P1297L mutation associated with hereditary megaloblastic anemia 1 causes impaired recognition of intrinsic factor-vitamin B(12) by cubilin. Blood 2000, 96, 405–409.
- Storm, T.; Emma, F.; Verroust, P.J.; Hertz, J.M.; Nielsen, R.; Christensen, E.I. A patient with cubilin deficiency. N. Engl. J. Med. 2011, 364, 89–91, doi:10.1056/NEJMc1009804.
- Hammad, S.M.; Stefansson, S.; Twal, W.O.; Drake, C.J.; Fleming, P.; Remaley, A.; Brewer, H.B., Jr.; Argraves, W.S. Cubilin, the endocytic receptor for intrinsic factor-vitamin B(12) complex, mediates high-density lipoprotein holoparticle endocytosis. Proc. Natl. Acad. Sci. USA 1999, 96, 10158–10163, doi:10.1073/pnas.96.18.10158.
- Honein, M.A.; Paulozzi, L.J.; Mathews, T.J.; Erickson, J.D.; Wong, L.Y. Impact of folic acid fortification of the US food supply on the occurrence of neural tube defects. JAMA 2001, 285, 2981–2986, doi:10.1001/jama.285.23.2981.
- Garcia, M.M.; Gueant-Rodriguez, R.M.; Pooya, S.; Brachet, P.; Alberto, J.M.; Jeannesson, E.; Maskali, F.; Gueguen, N.; Marie, P.Y.; Lacolley, P.; et al. Methyl donor deficiency induces cardiomyopathy through altered methylation/acetylation of PGC-1alpha by PRMT1 and SIRT1. J. Pathol. 2011, 225, 324–335, doi:10.1002/path.2881.
- Beaudin, A.E.; Perry, C.A.; Stabler, S.P.; Allen, R.H.; Stover, P.J. Maternal Mthfd1 disruption impairs fetal growth but does not cause neural tube defects in mice. Am. J. Clin. Nutr. 2012, 95, 882–891, doi:10.3945/ajcn.111.030783.
- Swanson, D.A.; Liu, M.L.; Baker, P.J.; Garrett, L.; Stitzel, M.; Wu, J.; Harris, M.; Banerjee, R.; Shane, B.; Brody, L.C. Targeted disruption of the methionine synthase gene in mice. Mol. Cell. Biol. 2001, 21, 1058–1065, doi:10.1128/MCB.21.4.1058-1065.2001.
- Deng, L.; Elmore, C.L.; Lawrance, A.K.; Matthews, R.G.; Rozen, R. Methionine synthase reductase deficiency results in adverse reproductive outcomes and congenital heart defects in mice. Mol. Genet. Metab. 2008, 94, 336–342, doi:10.1016/j.ymgme.2008.03.004.
- Chen, Z.; Karaplis, A.C.; Ackerman, S.L.; Pogribny, I.P.; Melnyk, S.; Lussier-Cacan, S.; Chen, M.F.; Pai, A.; John, S.W.; Smith, R.S.; et al. Mice deficient in methylenetetrahydrofolate reductase exhibit hyperhomocysteinemia and decreased methylation capacity, with neuropathology and aortic lipid deposition. Hum. Mol. Genet. 2001, 10, 433–443, doi:10.1093/hmg/10.5.433.
- Chen, Z.; Schwahn, B.C.; Wu, Q.; He, X.; Rozen, R. Postnatal cerebellar defects in mice deficient in methylenetetrahydrofolate reductase. Int. J. Dev. Neurosci. 2005, 23, 465–474, doi:10.1016/j.ijdevneu.2005.05.007.
- Jadavji, N.M.; Deng, L.; Leclerc, D.; Malysheva, O.; Bedell, B.J.; Caudill, M.A.; Rozen, R. Severe methylenetetrahydrofolate reductase deficiency in mice results in behavioral anomalies with morphological and biochemical changes in hippocampus. Mol. Genet. Metab. 2012, 106, 149–159, doi:10.1016/j.ymgme.2012.03.020.
- Li, D.; Pickell, L.; Liu, Y.; Wu, Q.; Cohn, J.S.; Rozen, R. Maternal methylenetetrahydrofolate reductase deficiency and low dietary folate lead to adverse reproductive outcomes and congenital heart defects in mice. Am. J. Clin. Nutr. 2005, 82, 188–195.
- Peters, H.; Nefedov, M.; Sarsero, J.; Pitt, J.; Fowler, K.J.; Gazeas, S.; Kahler, S.G.; Ioannou, P.A. A knock-out mouse model for methylmalonic aciduria resulting in neonatal lethality. J. Biol. Chem. 2003, 278, 52909–52913, doi:10.1074/jbc.M310533200.
- Chandler, R.J.; Zerfas, P.M.; Shanske, S.; Sloan, J.; Hoffmann, V.; DiMauro, S.; Venditti, C.P. Mitochondrial dysfunction in mut methylmalonic acidemia. FASEB J. 2009, 23, 1252–1261, doi:10.1096/fj.08-121848.
- Chandler, R.J.; Venditti, C.P. Adenovirus-mediated gene delivery rescues a neonatal lethal murine model of Mut(0) methylmalonic acidemia. Hum. Gene Ther. 2008, 19, 53–60, doi:10.1089/hum.2007.0118.
- Chandler, R.J.; Venditti, C.P. Pre-clinical efficacy and dosing of an AAV8 vector expressing human methylmalonyl-CoA mutase in a murine model of methylmalonic acidemia (MMA). Mol. Genet. Metab. 2012, 107, 617–619, doi:10.1016/j.ymgme.2012.09.019.
- Senac, J.S.; Chandler, R.J.; Sysol, J.R.; Li, L.; Venditti, C.P. Gene therapy in a murine model of methylmalonic acidemia using rAAV9-mediated gene delivery. Gene Ther. 2012, 19, 385–391, doi:10.1038/gt.2011.108.
- Carrillo-Carrasco, N.; Chandler, R.J.; Chandrasekaran, S.; Venditti, C.P. Liver-directed recombinant adeno-associated viral gene delivery rescues a lethal mouse model of methylmalonic acidemia and provides long-term phenotypic correction. Hum. Gene Ther. 2010, 21, 1147–1154, doi:10.1089/hum.2010.008.
- Peters, H.L.; Pitt, J.J.; Wood, L.R.; Hamilton, N.J.; Sarsero, J.P.; Buck, N.E. Mouse models for methylmalonic aciduria. PLoS One 2012, 7, e40609.
- Buck, N.E.; Dashnow, H.; Pitt, J.J.; Wood, L.R.; Peters, H.L. Development of transgenic mice containing an introduced stop codon on the human methylmalonyl-CoA mutase locus. PLoS One 2012, 7, e44974.
- Xu, Y.; Li, L.; Zhang, Z.; Li, Y. Effects of folinic acid and Vitamin B12 on ethanol-induced developmental toxicity in mouse. Toxicol. Lett. 2006, 167, 167–172, doi:10.1016/j.toxlet.2006.07.341.
- Lu, S.J.; He, W.; Shi, B.; Meng, T.; Li, X.Y.; Liu, Y.R. A preliminary study on the teratogenesis of dexamethasone and the preventive effect of vitamin B12 on murine embryonic palatal shelf fusion in vitro. J. Zhejiang Univ. Sci. B 2008, 9, 306–312, doi:10.1631/jzus.B0710625.
- He, W.; Meng, T.; Wu, M.; Shi, B.; Lu, S.J.; Li, C.H. Perturbation of Fgf10 signal pathway in mouse embryonic palate by dexamethasone and vitamin B12 in vivo. J. Pediatr. Surg. 2010, 45, 2030–2035, doi:10.1016/j.jpedsurg.2010.05.018.
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