Polymorphisms in the methylenetetrahydrofolate reductase gene: clinical consequences

Diffuse multicystic encephalomalacia in a preterm baby due to homozygous methylenetetrahydrofolate reductase 677 C-->T mutation

Methylenetetrahydrofolate reductase catalyzes the formation of 5-methyltetrahydrofolate from 5,10-methylentetrahydrofolate and produces folate for the methylation of homocysteine to methionine. Due to insufficient conversion of homocysteine to methionine, plasma homocysteine levels increase in methylenetetrahydrofolate reductase deficiency. Homocysteine is an amino acid that contains a neurotoxic sulfur molecule and can induce neuronal apoptosis. Methylenetetrahydrofolate reductase deficiency is 1 of the etiological factors that causes neurological symptoms and signs in the newborn and childhood period. Here, we report a premature baby with prenatal onset diffuse multicystic encephalomalacia and cerebellar atrophy due to homozygous methylenetetrahydrofolate reductase mutation.

Mechanisms of antifolate resistance and methotrexate efficacy in leukemia cells

Antifolates are the first class of antimetabolites introduced to clinic about 6 decades ago. Now, after several years of administration of antifolates against malignancies and particularly leukemia, we are still trying to achieve a full understanding of the mechanisms of action and resistance to these agents. The present article covers different factors able to influence efficacy of antifolates on leukemic cells, the known mechanisms of resistance to methotrexate (MTX) and strategies to overcome these mechanisms. The dominant factors that are contributed to tolerance to cytocidal effects of MTX including pharmacokinetic factors, impaired transmembrane uptake as the most frequent rote of provoking resistance to MTX, augmented drug efflux, impaired intracellular polyglutamation as a determining process of drug efficacy, alterations in expression or activity of target enzymes and increased intracellular folate pools; and finally role of 7-hydroxymethotrexate on response or resistance to MTX will be discussed in more detail. Finally, strategies to overcome resistance to antifolates are discussed.

Folate pathway genetic polymorphisms are related to attention disorders in childhood leukemia survivors

OBJECTIVE

To test the hypothesis that 5,10-methylenetetrahydroreductase (MTHFR) polymorphisms can partially explain the individual variation in developing attention-deficit/hyperactivity disorder (ADHD) after acute lymphoblastic leukemia (ALL) therapy.

STUDY DESIGN

Parents of 48 survivors of childhood ALL completed a clinical diagnostic process to identify subtypes of ADHD. Genotyping was performed with peripheral blood DNA for MTHFR (C677T and A1298C) polymorphisms.

RESULTS

Eleven of the 48 patients (22.9%) had scores consistent with the inattentive symptoms of ADHD. Patients with genotypes related to lower folate levels (11 out of 39; 39.2%) were more likely to have ADHD. The A1298C genotype appeared to be the predominant linkage to the inattentive symptoms, leading to a 7.4-fold increase in diagnosis, compared with a 1.3-fold increase for the C677T genotype. Age at diagnosis and sex were not associated with inattentiveness.

CONCLUSIONS

Preliminary data imply a strong relationship between MTHFR polymorphisms and the inattentive symptoms of ADHD in survivors of childhood ALL.

Relation between plasma homocysteine, gene polymorphisms of homocysteine metabolism-related enzymes, and angiographically proven coronary artery disease

BACKGROUND

Hyperhomocyteinemia (HHcy) is a risk factor for coronary artery disease (CAD), and methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MTR), and methionine synthase reductase (MTRR) polymorphisms may contribute to plasma total homocysteine (tHcy) variation. We investigated the association of polymorphisms 1298A-->C in the MTHFR gene, 2756A-->G in the MTR gene, and 66A-->G in the MTRR gene with tHcy levels and with CAD in patients undergoing coronary angiography.

METHODS

CAD patients (n=151) and control subjects (n=79) were compared regarding the prevalence of the polymorphisms, risk factors, and biochemical parameters.

RESULTS

The mean tHcy concentration was significantly higher in CAD patients than in control subjects (P<0.001). HHcy (tHcy>/=15 mumol/l) conferred an OR of CAD of 4.1 (95% CI 2.2-7.5, P<0.001). In both cases and controls, smokers had a higher tHcy level than non-smokers and demonstrated a markedly increased risk for CAD (OR=2.5, 95% CI 1.7-3.3, P<0.001). The allele frequencies of the MTHFR 1298A-->C, MTR 2756A-->G, and MTRR 66A-->G mutations were 36.7%, 15.7%, and 36.6%, respectively. The 1298C allele frequency was significantly higher in the CAD group than in controls (P<0.05) and showed a significant association with CAD in heterozygote carriers. There was no statistically significant difference between cases and controls in the frequencies of the A2756G alleles/genotypes in the MTR gene and of the A66G alleles/genotypes in the MTRR gene. The contributions to tHcy levels of the three common mutations were statistically significant. The heterozygosity of the MTHFR 1298AC genotype, MTR 2756G allele, and MTRR 66G allele yielded an OR of 3.4, 2.0, and 2.1, respectively, for having HHcy.

CONCLUSION

We suggest that HHcy confers a risk for CAD, and smokers with tHcy are at a greatly increased risk. Our finding supports an important role of the MTHFR gene in CAD and provides evidence of polygenic regulation of tHcy.

Personalized nutrition: nutritional genomics as a potential tool for targeted medical nutrition therapy

An emerging goal of medical nutrition therapy is to tailor dietary advice to an individual's genetic profile. In the United States and elsewhere, "nutrigenetic" services are available over the Internet without the direct involvement of a health care professional. Among the genetic variants most commonly assessed by these companies are those found in genes that influence cardiovascular disease risk. However, the interpretation of DNA-based data is complex. The goal of this paper is to carefully examine nutritional genomics as a potential tool for targeted medical nutrition therapy. The approach is to use heart health susceptibility genes and their common genetic variants as the model.

Pharmacogenomics of acute leukemia

Pharmacogenomics provides knowledge regarding how genetic polymorphisms affect treatment responses. Such an approach is particularly needed in cancer therapy, as most chemotherapeutics drugs affect both tumor and normal cells, are ineffective in many patients and exhibit serious side effects. Leukemia exists in two different forms, myeloid and lymphoid. Acute lymphoblastic leukemia more frequently occurs in children, whereas the risk of acute myeloid leukemia is more common in adults. Despite significant progress in the treatment of these diseases, therapy is still unsuccessful in many patients. Prognosis is particularly poor in adult acute myeloid leukemia. Treatment failure in childhood acute lymphoblastic leukemia due to drug resistance remains the leading cause of cancer-related death in children. Here, we provide an overview of pharmacogenetics studies carried out in children and adults with acute lymphoblastic leukemia and acute myeloid leukemia, attempting to find the associations between treatment responses and polymorphisms in the genes whose products are needed for metabolism, and effects of drugs used in the treatment of leukemia.

Pharmacogenomics in cancer treatment defining genetic bases for inter-individual differences in responses to chemotherapy

PURPOSE OF REVIEW

Pharmacogenomics is evolving rapidly due to the expansion of genomics and proteomics, the emerging technologies, knowledge of the molecular basis of neoplasms and of drug pathways. This article will give an update on the genetic basis of variable therapeutic responses to anticancer agents in children.

RECENT FINDINGS

The majority of recent findings concern the pharmacogenetics of key components of acute lymphoblastic leukemia treatment, 6-mercaptopurine and methotrexate. This is not surprising given that leukemia is the most common cancer affecting children, accounting for 25-35% of childhood malignancies worldwide with acute lymphoblastic leukemia comprising 80% of leukemia cases. In certain patients treatment fails due to drug resistance, rendering acute lymphoblastic leukemia the leading cause of cancer-related death in children. Most of the studies use a candidate gene approach adding a new body of evidence to existing knowledge. Recent findings relating to other childhood tumors and the potential to optimize treatment of these malignancies are briefly discussed.

SUMMARY

Interindividual differences in drug responses are an important cause of resistance to treatment and adverse drug reactions. Pharmacogenetics tends to identify the genetic basis of these suboptimal responses allowing traditional treatment to be complemented by genotype-based drug dose adjustment.

Molecular phylogenetic analysis of methylenetetrahydrofolate reductase family of proteins

Methylenetetrahydrofolate reductase (MTHFR) family of proteins catalyze the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate. They contain a flavin adenine dinucleotide (FAD) as the cofactor and the enzyme in eukaryotes, except in yeast, is known to be allosterically regulated by S-adenosylmethionine. Some cardiovascular diseases, neural tube defects, neuropsychiatric diseases and certain type of cancers in humans are associated with certain polymorphisms of MTHFR. Here, we analyzed 57 of MTHFR polypeptide sequences by multiple sequence alignment and determined previously unrecognized conserved residues that may have a functional or structural importance. A previously unrecognized ATP synthase motif was found in all of the examined plant MTHFRs, suggesting a different functional capability to the plant MTHFRs in addition to the known function. On a phylogenetic tree built, eukaryotic MTHFR proteins formed a clear cluster separated from prokaryotic and archeal relatives. The sequence identities among the eukaryotic MTHFRs were less divergent than the bacterial MTHFRs.

A proteomic approach for the characterization of C677T mutation of the human gene methylenetetrahydrofolate reductase

Methylenetetrahydrofolate reductase (MTHFR) catalyzes the conversion of methylenetetrahydrofolate (CH2H4folate) to methyltetrahydrofolate (CH3H4folate). The C677T mutation is a common polymorphism of the human enzyme that leads to the replacement of Ala222Val, thermolability of MTHFR, and mild elevation of plasma homocysteine levels. A mild hyperhomocysteinemia is known to be risk factor for cardiovascular and thrombotic diseases, ischemic stroke, neural tube defects, late on-set dementia, and pregnancy complications. Human plasma of subjects carrying the C677T mutation in the MTHFR gene has been investigated for their protein pattern in order to identify novel molecular hallmarks. 2-D analysis of the plasma protein allowed the identification of a specific pattern associated with the TT mutant genotype. Noteworthy, we found one spot shifted to a more basic pI in mutant individuals, and MS identification corresponded to vitamin D-binding protein (DBP or group component (Gc) globulin). MS/MS peptide sequencing allowed to discriminate different allelic variants in the investigated clinical groups. These data confirmed by molecular genetic analysis highlight the novel association between the C677T MTHFR genotype with the Gc2 polymorphism of the DBP. Moreover, we found a quantitative reduction of Apolipoprotein A-I in mutant individuals, which was associated, in previous studies by others to an increased cardiovascular risk.

Racial or ethnic differences in allele frequencies of single-nucleotide polymorphisms in the methylenetetrahydrofolate reductase gene and their influence on response to methotrexate in rheumatoid arthritis

BACKGROUND

The anti-folate drug methotrexate (MTX) is commonly used to treat rheumatoid arthritis.

OBJECTIVE

To determine the allele frequencies of five common coding single-nucleotide polymorphisms (SNPs) in the methylenetetrahydrofolate reductase (MTHFR) gene in African-Americans and Caucasians with rheumatoid arthritis and controls to assess whether there are differences in allele frequencies among these ethnic or racial groups and whether these SNPs differentially affect the efficacy or toxicity of MTX.

METHODS

Allele frequencies in the 677, 1298 and 3 additional SNPs in the MTHFR coding region in 223 (193 Caucasians and 30 African-Americans) patients with rheumatoid arthritis who previously participated in one of two prospective clinical trials were characterised, and genotypes were correlated with the efficacy and toxicity of MTX. Another 308 subjects with rheumatoid arthritis who participated in observational studies, one group predominantly Caucasian and the other African-American, as well as 103 normal controls (53 African-Americans and 50 Caucasians) were used to characterise allele frequencies of these SNPs and their associated haplotypes.

RESULTS

Significantly different allele frequencies were seen in three of the five SNPs and haplotype frequencies between Caucasians and African-Americans. Allele frequencies were similar between patients with rheumatoid arthritis and controls of the same racial or ethnic group. Frequencies of the rs4846051C, 677T and 1298C alleles were 0.33, 0.11 and 0.13, respectively, among African-Americans with rheumatoid arthritis. Among Caucasians with rheumatoid arthritis, these allele frequencies were 0.08 (p<0.001 compared with African-Americans with rheumatoid arthritis), 0.30 (p = 0.002) and 0.34 (p<0.001), respectively. There was no association between SNP alleles or haplotypes and response to MTX as measured by the mean change in the 28-joint Disease Activity Score from baseline values. In Caucasians, the 1298 A (major) allele was associated with a significant increase in MTX-related adverse events characteristic of a recessive genetic effect (odds ratio 15.86, 95% confidence interval 1.51 to 167.01; p = 0.021), confirming previous reports. There was an association between scores of MTX toxicity and the rs4846051 C allele, and haplotypes containing this allele, in African-Americans, but not in Caucasians.

CONCLUSIONS

: These results, although preliminary, highlight racial or ethnic differences in frequencies of common MTHFR SNPs. The MTHFR 1298 A and the rs4846051 C alleles were associated with MTX-related adverse events in Caucasians and African-Americans, respectively, but these findings should be replicated in larger studies. The rs4846051 SNP, which is far more common in African-Americans than in Caucasians, can also be proved to be a useful ancestry informative marker in future studies on genetic admixture.

Methotrexate pharmacogenomics

Observations of clinical effects of methotrexate will help in patient‐management decisions

Challenges identifying genetic determinants of pediatric cancers--the childhood leukemia experience

Pediatric cancers affect approximately 1 in every 500 children before the age of 15. Little is known about the etiology of this heterogeneous group of diseases despite the fact they constitute the major cause of death by disease among this population. Because of its relatively high prevalence, most of the work done in pediatric oncogenetics has been focused on leukemias, particularly acute lymphoblastic leukemia (ALL). Although it is now well accepted that genetic variation plays a significant role in determining individual's cancer susceptibility, few studies have explored genetic susceptibility to childhood leukemia with respect to common polymorphisms. The biochemical and genetic mechanisms contributing to cancer susceptibility are numerous and can be grouped into broad categories: (1) cellular growth and differentiation, (2) DNA replication and repair, (3) metabolism of carcinogens (4) apoptosis, (5) oxidative stress response and (6) cell cycle. To evaluate whether candidate genes in these pathways are involved in childhood leukemogenesis, we conducted case-control studies. We showed that leukemogenesis in children may be associated with DNA variants in some of these genes and that the combination of genotypes seems to be more predictive of risk than either of them independently. We also observed that, at least at some loci, the parental genetics might be important in predicting the risk of cancer in this pediatric model of a complex disease. Taken together, these results indicate that the investigation of a single enzyme and/or a single genotype might not be sufficient to explain the etiology of childhood leukemia because of the complexity of the environment and that of the inter-individual variability in cancer susceptibility.

Analysis of MTHFR polymorphisms and P16 methylation and their correlation with clinical-biological features of multiple myeloma

BACKGROUND

Low folate intake and changes in folate metabolism due to polymorphisms in the methylentetrahydrofolate reductase (MTHFR) gene have been associated with myelomagenesis. However, controversial data have been published regarding a protective role of variant alleles of MTHFR on MM.

PATIENTS AND METHODS

To investigate the influence of two common polymorphisms of MTHFR C677T and A1298C on the risk of multiple myeloma (MM), we performed a matched case-control study. The methylation status pattern of p16 was also addressed.

RESULTS

The frequency each of 677 CC, 677CT, and 677TT was 31, 44, and 25%, respectively, whereas, the frequency each of 1298 AA, AC, CC was 48, 44, and 8% in MM patients. In the control group, the frequency each of 677CC, 677CT, and 677TT was 36, 45, and 19%, respectively, while the frequency each of 1298 AA, AC, CC was 37, 50, and 13%, respectively. No significant association between susceptibility to MM, 677, and 1298 MTHFR variants was detected. As regards p16 methylation, we confirmed a high prevalence of p16 methylation (40%) in patients affected by MM and demonstrated that MTHFR 677CC is associated with a higher prevalence of p16 hypermethylation.

CONCLUSIONS

Our data demonstrated that variant alleles did not play a key role neither in protection nor in increased risk for MM, suggesting that the effect of MTHFR on folate metabolism might be modified by diet intake. Moreover, our findings demonstrated that p16 hypermethylation might be a frequent genetic aberration in MM and may contribute with other molecular aberrations in the pathogenesis of this malignant disorder.

Magnetic resonance angiography of abdominal and lower extremity vasculature

Magnetic resonance angiography (MRA) has evolved over the past years from an experimental imaging modality to a technique that is now widely applied in clinical practice. This article reviews the fundamentals of the different magnetic resonance angiographic techniques and how they can be applied for abdominal and peripheral arterial imaging. Currently, contrast-enhanced magnetic resonance angiography (CE-MRA), whereby a luminogram is obtained during initial arterial passage of contrast material, is the most widely used technique. With current hardware and software, high-spatial resolution images of the abdominal aorta and proximal visceral branches can be obtained that are equivalent to intra-arterial digital subtraction angiography (IA-DSA). High-quality imaging of the renal arteries demands isotropic voxels and reformations orthogonal to the vessel axis for evaluation. Contrast-enhanced magnetic resonance angiography of the peripheral vascular tree is now a highly accurate technique and has replaced diagnostic intra-arterial digital subtraction angiography and duplex ultrasonography in many hospitals.

Polymorphisms in the reduced folate carrier, thymidylate synthase, or methionine synthase and risk of colon cancer

Folate metabolism supports the synthesis of nucleotides as well as the transfer of methyl groups. Polymorphisms in folate-metabolizing enzymes have been shown to affect risk of colorectal neoplasia and other malignancies. Using data from a population-based incident case-control study (1,600 cases and 1,962 controls), we investigated associations between genetic variants in the reduced folate carrier (RFC), thymidylate synthase (TS), methionine synthase (MTR), and 5,10-methylenetetrahydrofolate reductase (MTHFR) and colon cancer risk. The TS enhancer region (TSER) variant was associated with a reduced risk among men [2rpt/2rpt versus 3rpt/3rpt wild-type; odds ratio (OR), 0.7; 95% confidence interval, 0.6-0.98] but not women. When combined genotypes for both TS polymorphisms (TSER and 3'-untranslated region 1494delTTAAAG) were evaluated, ORs for variant genotypes were generally below 1.0, with statistically significantly reduced risks among women. Neither MTR D919G nor RFC 80G>A polymorphisms were associated with altered colon cancer risk. Because folate metabolism is characterized by interrelated reactions, we evaluated gene-gene interactions. Genotypes resulting in reduced MTHFR activity in conjunction with low TS expression were associated with a reduced risk of colon cancer. When dietary intakes were taken into account, individuals with at least one variant TSER allele (3rpt/2rpt or 2rpt/2rpt) were at reduced risk in the presence of a low folate intake. This study supports findings from adenoma studies indicating that purine synthesis may be a relevant biological mechanism linking folate metabolism to colon cancer risk. A pathway-based approach to data analysis is needed to help discern the independent and combined effects of dietary intakes and genetic variability in folate metabolism.

Emerging concepts in nutrigenomics: a preview of what is to come

This article provides an overview of the fundamental principles of genetics and emerging concepts related to the ways in which nutrients and bioactive food components may interact with the genome and subsequently affect human health. This exciting area of research is likely to have far-reaching implications for the assessment and treatment of critically and chronically ill individuals that will affect nutrition standards of care and practice. A brief overview of some of the ethical, legal, and social implications of genomic research and genome-based health care and a list of genetics resources also are provided.

The pharmacogenetics of methotrexate in inflammatory bowel disease

OBJECTIVES

Methotrexate (MTX) is an effective immunosuppressive treatment in inflammatory bowel disease (IBD) but its use is limited by unpredictable toxicity and efficacy. MTX metabolism is complex involving a number of enzymes. An individual's response to MTX may in part be genetically determined by functional genetic variation in genes encoding these enzymes. We report a pharmacogenetic evaluation of MTX therapy in IBD.

METHODS

We studied 102 IBD patients treated with MTX, and 202 patients with Crohn's disease (CD), 205 patients with ulcerative colitis (UC) and 189 healthy volunteers served as controls to assess allele frequencies in the disease and healthy populations. All subjects were genotyped for four polymorphisms: G80A in the reduced folate carrier (RFC1) gene, G452T in the gamma-glutamyl hydrolase (GGH) gene and C677T and A1298C in the methylenetetrahydrofolate reductase (MTHFR) gene. Three non-conservative SNPs in the RFC1 and the MTHFR gene could not be detected in our patient cohort. Genotype-phenotype associations were evaluated with respect to efficacy and toxicity of MTX therapy.

RESULTS

No significant differences in the allele frequencies between CD, UC and healthy controls were detected. Overall 21% of patients experienced MTX side effects. Patients homozygous for the MTHFR 1298C allele were more likely to experience one or more side effects compared to patients with the wild-type 1298AA genotype (21.0 vs. 6.3%, P < 0.05). None of the genotyped SNPs or haplotypes, either alone or in combination, was associated with short-term efficacy or sustained response.

CONCLUSIONS

Side effects of MTX in IBD are associated with a SNP in the MTHFR gene but response cannot be predicted by any of the investigated SNPs.

Roles of methylenetetrahydrofolate reductase C677T polymorphism in repeated pregnancy loss

Congenital thrombophilia in repeated pregnancy lost (RPL) has been noted for years. Methylenetetrahydrofolate reductase (MTHFR) gene is an interesting gene, mentioned for its possible roles in RPL. There is considerable controversy regarding the clinical role of MTHFR C677T polymorphism as a risk factor of RPL. Here, a summative analysis is performed on the recent previous reports on the MTHFR C677T and its correlation to RPL. The metanalysis was performed to assess the correlation between the pattern of MTHFR C677T polymorphism and RPL. From available eight case-control studies, 752 patients and 625 controls are evaluated. The overall frequencies of 4G allele for the patients and controls are 31.5 and 33.5, respectively. According to this study, 53.1% of subjects with T allele have RLP while 55.3% of subjects without T allele have RLP. From overall risk estimation, the subjects with T alleles have 0.96 times lower risk to RLP. According to this analysis, the pattern of MTHFR C677T polymorphism might not represent a useful marker of increased risk for RPL. In addition, there was no association between pattern of MTHFR C677T polymorphism and ethnicity of the patients in this study.

German vegan study: diet, life-style factors, and cardiovascular risk profile

BACKGROUND/AIM

Evaluation of cardiovascular risk profile in 154 German vegans.

METHODS

Cross-sectional study, Germany. Study instruments: 2 FFQ, 2 questionnaires, analyses of fasting venous blood samples.

RESULTS

The total study population had a low BMI (mean: 22.3 kg/m(2)), a moderate blood pressure (mean: 120/75 mm Hg), an extremely low consumption of alcohol (mean: 0.77 g/day) and 96.8% were nonsmokers. Moderate physical activity (PAL) was reported by nearly 50%, whereas 22.7% declared to have a high PAL (>3 h/week). Median triacylglycerol (TG) was 0.81 mmol/l, total cholesterol (TC) was 4.33 mmol/l, HDL was 1.34 mmol/l. The mean TC/HDL-ratio was 3.3. Lipoprotein(a) (Lp(a)) was 8.13 mg/dl, concentrations of >30 mg/dl were prevalent in 25% of the participants. In general, status of folate and pyridoxine were sufficient, while 49.7% showed cobalamin concentrations <150 pmol/l. Plasma homocysteine levels were slightly elevated (median: 12.5 micromol/l). Cobalamin concentration and duration of vegan nutrition were the main determinants of homocysteine in the total study population.

CONCLUSION

Although TC and LDL concentrations were favorable, low HDL and elevated homocysteine and Lp(a) concentrations were unfavorable. Overall, these results confirm the notion that a vegan diet is deficient in vitamin B(12), which may have an unfavorable effect on CHD risk.

Homocysteine and folate metabolism in depression

Homocysteine is a sensitive marker of folate and vitamin B12 deficiency. Numerous studies have confirmed the association between folate deficiency and depression. It is not completely understood whether homocysteine is solely a marker for folate deficiency or if it may play a more direct role in the expression of mood disorders. This review describes the biochemical, neurochemical and clinical correlations of folate deficiency and hyperhomocysteinemia in relation to depression.

Maternal mutation 677C > T in the methylenetetrahydrofolate reductase gene associated with severe brain injury in offspring

A frequent polymorphism in the gene coding for 5,10-methylenetetrahydrofolate reductase is the substitution 677C > T which produces a thermolabile and inefficient enzyme. Homozygosity for the 677C > T allele is the most important determinant of hyperhomocys-teinemia, when folic acid intake is reduced. Most studies on the relationship between the 677C > T variant in the mother and defects in the offspring have focused on neural-tube defects. This study is a retrospective case-control investigation of hypoxic-ischemic encephalopathy of the newborn (HIEN) with reference to the 677C > T polymorphism as a genetic risk for this condition. The prevalence of the 677C > T allele was studied in 11 children with HIEN, their respective mothers, and 85 healthy individuals. Plasma homocysteine levels after fasting and methionine loading were determined in both mothers and controls. Ten of 11 patients were evaluated using magnetic resonance (MR) imaging, and all showed multicystic encephalomalacia and severe brain vasculopathy. Seven mothers were homozygous and four heterozygous for the 677C > T allele. Five of the children were homozygous and six heterozygous for this polymorphism. The variant allele frequency was higher in the group of mothers with affected children than in the controls and was associated with an increase in plasma homocysteine after methionine loading, in the group of mothers than in controls. The 677C > T mutation in mothers, either in a homozygous or heterozygous state, together with poor nutritional status (probable folate deficiency) may represent a risk factor for irreversible HIEN in the offspring.

Comparative folate metabolism in humans and malaria parasites (part II): activities as yet untargeted or specific to Plasmodium

The folate pathway represents a powerful target for combating rapidly dividing systems such as cancer cells, bacteria and malaria parasites. Whereas folate metabolism in mammalian cells and bacteria has been studied extensively, it is understood less well in malaria parasites. In two articles, we attempt to reconstitute the malaria folate pathway based on available information from mammalian and microbial systems, in addition to Plasmodium-genome-sequencing projects. In part I, we focused on folate enzymes that are already used clinically as anticancer drug targets or that are under development in drug-discovery programs. In this article, we discuss mammalian folate enzymes that have not yet been exploited as potential drug targets, and enzymes that function in the de novo folate-synthesis pathway of the parasite--a particularly attractive area of attack because of its absence from the mammalian host.

Postnatal cerebellar defects in mice deficient in methylenetetrahydrofolate reductase

Patients with severe deficiency of methylenetetrahydrofolate reductase (MTHFR) suffer from a wide variety of neurological problems, which can begin in the neonatal period. MTHFR is a critical enzyme in folate metabolism; the product of the MTHFR reaction, 5-methyltetrahydrofolate, is required for homocysteine remethylation to methionine and synthesis of S-adenosylmethionine (SAM). To understand the mechanisms by which MTHFR deficiency leads to significant neuropathology, we examined early postnatal brain development in mice with a homozygous knockout of the Mthfr gene. These mice displayed a dramatically reduced size of the cerebellum and cerebral cortex, with enlarged lateral ventricles. Mthfr deficiency affected granule cell maturation, but not neurogenesis. Depletion of external granule cells and disorganization of Purkinje cells were mainly confined to the anterior lobules of mutant cerebella. Decreased cellular proliferation and increased cell death contributed to the granule cell loss. Reduced expression of Engrailed-2 (En2), Reelin (Reln) and inositol 1,4,5-triphosphate receptor type 1 (Itpr1) genes was observed in the cerebellum. Supplementation of Mthfr(+/-) dams with an alternate methyl donor, betaine, reduced cerebellar abnormalities in the Mthfr(-/-) pups. Our findings suggest that MTHFR plays a role in cerebellar patterning, possibly through effects on proliferation or apoptosis.

A fragile site at 10q23 (FRA10A) in a phenytoin-exposed fetus: a case report and review of the literature

OBJECTIVE

To report fragility at 10q23.3 in a fetus exposed to phenytoin during pregnancy. Review of the literature.

METHODS

Amniocytes were cultured in A10 (WISENT) culture medium. Molecular polymorphism studies of MTHFR gene using PCR were performed on fetal tissues.

RESULTS

The fragile site was expressed in all 22 amniocyte colonies analyzed. Analysis of fetal blood showed 46,XX[98]/46,XX,fra(10)(q23.3)[3]/46,XX,del(10)(q23.3) [1]. Molecular studies of the MTHFR (methylenetetrahydrofolate reductase) gene identified a compound heterozygote genotype for two polymorphisms, 677C>T and 1298A>C.

CONCLUSION

The fragility at 10q23.3 is unlikely to be due to culture condition-induced folic acid deficiency (medium contains folate). It is possible that this finding represents a previously undescribed folic acid-insensitive fragile site in the region of 10q23.3. Alternatively, the fetal cells may have had decreased folate metabolism, and the fragile site was the known folate-sensitive FRA10A. Since phenytoin has been shown to decrease MTHFR activity in mice, we postulate that the fragile site at 10q23.3 in this fetus may have arisen secondary to a combination of the polymorphisms in MTHFR and exposure to this drug, and is indeed FRA10A.

Betaine rescue of an animal model with methylenetetrahydrofolate reductase deficiency

MTHFR (methylenetetrahydrofolate reductase) catalyses the synthesis of 5-methyltetrahydrofolate, the folate derivative utilized in homocysteine remethylation to methionine. A severe deficiency of MTHFR results in hyperhomocysteinaemia and homocystinuria. Betaine supplementation has proven effective in ameliorating the biochemical abnormalities and the clinical course in patients with this deficiency. Mice with a complete knockout of MTHFR serve as a good animal model for homocystinuria; early postnatal death of these mice is common, as with some neonates with low residual MTHFR activity. We attempted to rescue Mthfr-/- mice from postnatal death by betaine supplementation to their mothers throughout pregnancy and lactation. Betaine decreased the mortality of Mthfr-/- mice from 83% to 26% and significantly improved somatic development from postnatal day 1, compared with Mthfr-/- mice from unsupplemented dams. Biochemical evaluations demonstrated higher availability of betaine in suckling pups, decreased accumulation of homocysteine, and decreased flux through the trans-sulphuration pathway in liver and brain of Mthfr-/- pups from betaine-supplemented dams. We observed disturbances in proliferation and differentiation in the cerebellum and hippocampus in the knockout mice; these changes were ameliorated by betaine supplementation. The dramatic effects of betaine on survival and growth, and the partial reversibility of the biochemical and developmental anomalies in the brains of MTHFR-deficient mice, emphasize an important role for choline and betaine depletion in the pathogenesis of homocystinuria due to MTHFR deficiency.

Betaine rescue of an animal model with methylenetetrahydrofolate reductase deficiency

MTHFR (methylenetetrahydrofolate reductase) catalyses the synthesis of 5-methyltetrahydrofolate, the folate derivative utilized in homocysteine remethylation to methionine. A severe deficiency of MTHFR results in hyperhomocysteinaemia and homocystinuria. Betaine supplementation has proven effective in ameliorating the biochemical abnormalities and the clinical course in patients with this deficiency. Mice with a complete knockout of MTHFR serve as a good animal model for homocystinuria; early postnatal death of these mice is common, as with some neonates with low residual MTHFR activity. We attempted to rescue Mthfr-/- mice from postnatal death by betaine supplementation to their mothers throughout pregnancy and lactation. Betaine decreased the mortality of Mthfr-/- mice from 83% to 26% and significantly improved somatic development from postnatal day 1, compared with Mthfr-/- mice from unsupplemented dams. Biochemical evaluations demonstrated higher availability of betaine in suckling pups, decreased accumulation of homocysteine, and decreased flux through the trans-sulphuration pathway in liver and brain of Mthfr-/- pups from betaine-supplemented dams. We observed disturbances in proliferation and differentiation in the cerebellum and hippocampus in the knockout mice; these changes were ameliorated by betaine supplementation. The dramatic effects of betaine on survival and growth, and the partial reversibility of the biochemical and developmental anomalies in the brains of MTHFR-deficient mice, emphasize an important role for choline and betaine depletion in the pathogenesis of homocystinuria due to MTHFR deficiency.

Pharmacogenetics of methotrexate

Methotrexate (MTX) has proven efficient in the treatment of a number of malignancies, as well as non-malignant disorders characterized by a rapid cellular growth. Yet some patients might develop resistance, while others could have toxic side effects. MTX achieves its cytotoxicity through the inhibition of folate-dependent enzymes, suggesting that the genes controlling their activity or the levels of folate cofactors can modulate drug efficacy and, thus, the sensitivity of a patient to MTX. Indeed, several studies, conducted mostly in leukemia and rheumatoid arthritis patients, have addressed the potential for tailoring MTX therapy based on a patient's genetics. Several genetic variants have been shown to have a predictive role, among which the most frequently studied are those of methylenetetrahydrofolate reductase and thymidylate synthase genes. The other candidates, as well as gene-gene interactions, which may be even more important for the prediction of disease outcomes than the individual gene effects, are also briefly discussed.

Detection of genomic polymorphisms associated with venous thrombosis using the invader biplex assay

A multi-site study to assess the accuracy and performance of the biplex Invader assay for genotyping five polymorphisms implicated in venous thrombosis was carried out in seven laboratories. Genotyping results obtained using the Invader biplex assay were compared to those obtained from a reference method, either allele-specific polymerase chain reaction (AS-PCR), restriction fragment length polymorphism (PCR-RFLP) or PCR-mass spectrometry. Results were compared for five loci associated with venous thrombosis: Factor V Leiden, Factor II (prothrombin) G20210A, methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C, and plasminogen activator inhibitor (PAI-1) 4G/5G. Of a total of 1448 genotypes tested in this study, there were 22 samples that gave different results between the Invader biplex assay and the PCR-based methods. On further testing, 21 were determined to be correctly genotyped by the Invader Assay and only a single discrepancy was resolved in favor of the PCR-based assays. The compiled results demonstrate that the Invader biplex assay provides results more than 99.9% concordant with standard PCR-based techniques and is a rapid and highly accurate alternative to target amplification-based methods.

Development of hygromas or severe edema during treatment with the tyrosine kinase inhibitor STI571 is not associated with platelet-derived growth factor receptor (PDGFR) gene polymorphisms

STI571 is active against Bcr/Abl-, c-kit- and platelet-derived growth factor receptor (PDGFR)-driven malignancies. Mild to moderate edema is common, whereas severe edema, body cavity effusions and subdural hygromas are rarely observed. These effects have been suggested to involve inhibition of PDGFR signaling, but predisposing factors are unknown. We examined SNPs in the PDGFR alpha and beta gene regions in STI571-treated patients with and without life-threatening edema or cerebral hygromas, and in healthy volunteers. By RFLP analysis of 15 SNPs, the frequencies of genotypes did not differ between the three groups. SNPs of PDGFR genes do not appear to play a role in patient's susceptibility to clinically severe edema formation during treatment with STI571.

Epigenetics and human disease

Epigenetics is comprised of the stable and heritable (or potentially heritable) changes in gene expression that do not entail a change in DNA sequence. The role of epigenetics in the etiology of human disease is increasingly recognized with the most obvious evidence found for genes subject to genomic imprinting. Mutations and epimutations in imprinted genes can give rise to genetic and epigenetic phenotypes, respectively; uniparental disomy and imprinting defects represent epigenetic disease phenotypes. There are also genetic disorders that affect chromatin structure and remodeling. These disorders can affect chromatin in trans or in cis, as well as expression of both imprinted and nonimprinted genes. Data from Angelman and Beckwith-Wiedemann syndromes and other disorders indicate that a monogenic or oligogenic phenotype can be caused by a mixed epigenetic and genetic and mixed de novo and inherited (MEGDI) model. The MEGDI model may apply to some complex disease traits and could explain negative results in genome-wide genetic scans.

Mice deficient in methylenetetrahydrofolate reductase exhibit tissue-specific distribution of folates

Methylenetetrahydrofolate reductase (MTHFR) catalyzes the synthesis of 5-methyltetrahydrofolate (5-methylTHF), which is used for homocysteine remethylation to methionine, the precursor of S-adenosylmethionine (SAM). Impairment of MTHFR will increase homocysteine levels and compromise SAM-dependent methylation reactions. Mild MTHFR deficiency is common in many populations due to a polymorphism at bp 677. To assess how impaired MTHFR activity affects folate metabolism in various tissues in vivo, we used affinity/HPLC with electrochemical detection to analyze the distribution of folates in plasma, liver, and brain of Mthfr-deficient mice. The most pronounced difference in total folate was observed in plasma. In Mthfr -/- mice, plasma total folate levels were approximately 25% of those in wild-type (Mthfr +/+) mice. Only 40% of plasma folate in Mthfr -/- mice was comprised of 5-methylTHF, compared with at least 80% in the other 2 genotype groups. In liver and brain, there were no differences in total folate. However, the proportion of 5-methylTHF in both tissues was again markedly reduced in mice with the Mthfr -/- genotype. In this genotype group, 5-methylTHF is likely derived from the diet. Our study demonstrated reduced total circulatory folate and altered distribution of folate derivatives in liver and brain in Mthfr deficiency. Decreased methylfolates and increased nonmethylfolates would affect the flux of one-carbon units between methylation reactions and nucleotide synthesis. This altered flux has implications for several common disorders, including cancer and vascular disease.

Mechanisms of non-alcoholic steatohepatitis

In 1980, the term non-alcoholic steatohepatitis was coined to describe a new syndrome occurring in patients who usually were obese (often diabetic) females who had a liver biopsy picture consistent with alcoholic hepatitis, but who denied alcohol use. The causes of this syndrome were unknown, and there was no defined therapy. More than two decades later, this clinical syndrome is only somewhat better understood, and still there is no Food and Drug Administration-approved or even generally accepted drug therapy. Patients with primary non-alcoholic steatohepatitis typically have the insulin resistance syndrome (synonymous with the metabolic syndrome, syndrome X, and so forth), which is characterized by obesity, diabetes, hyperlipidemia, hypertension, and, in some instances, other metabolic abnormalities such as polycystic ovary disease. Secondary non-alcoholic steatohepatitis may be caused by drugs such as tamoxifen, certain industrial toxins, rapid weight loss, and so forth. The cause of non-alcoholic steatohepatitis remains elusive, but most investigators agree that a baseline of steatosis requires a second hit capable of inducing inflammation, fibrosis, or necrosis for non-alcoholic steatohepatitis to develop. Our research group has focused its efforts on the interactions of nutritional abnormalities, cytokines, oxidative stress with lipid peroxidation, and mitochondrial dysfunction in the induction of steatohepatitis, both alcoholic and non-alcoholic in origin. Research findings from other laboratories also support the role of increased cytokine activity, oxidative stress, and mitochondrial dysfunction in the pathogenesis of non-alcoholic steatohepatitis. The objectives of this article are to review the (1) definition and clinical features of non-alcoholic steatohepatitis, (2) potential mechanisms of non-alcoholic steatohepatitis, and (3) potential therapeutic interventions in non-alcoholic steatohepatitis.

Characterization of a pseudogene for murine methylenetetrahydrofolate reductase

Methylenetetrahydrofolate reductase (MTHFR) reduces 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, the major carbon donor in the remethylation of homocysteine to methionine. Mild MTHFR deficiency, due to a common variant at nucleotide 677, has been reported to influence risk for several disorders including cardiovascular disease, neural tube defects, pregnancy complications and cancer. In recent work, we characterized the complete cDNA and gene sequences in the human and mouse genes, which had previously been mapped to chromosomes 1 and 4, respectively. During the course of this work, we observed that PCR primers in exons 1 and 2 of Mthfr generated amplicons of the expected size for the normal Mthfr transcript, using both reverse-transcribed RNA and genomic DNA as templates. These findings alluded to the existence of a pseudogene in the murine genome. Here, we report the characterization of this pseudogene. The absence of intron 1, the partial retention of intron 2, the location of this gene on chromosome 5, and the presence of sequences unrelated to Mthfr at the 5' and 3' ends of the 1259 bp fragment are features that are indicative of a partially-processed pseudogene, that we have designated Mthfr-ps. A Mthfr-ps transcript was not detectable by sensitive RT-PCR using assays designed to simultaneously detect the authentic Mthfr transcript. The structure of this paralogous gene and the identification of a repeat sequence at the 3' end of this pseudogene suggest that it arose by retrotransposition of a mis-spliced Mthfr transcript. Investigations of the Mthfr gene should take into account the presence of the non-functional Mthfr-ps to avoid misinterpretation of results.

Role of MTHFR genetic polymorphisms in the susceptibility to childhood acute lymphoblastic leukemia

The central role of methylenetetrahydrofolate reductase (MTHFR) in the folate metabolism renders MTHFR gene polymorphisms (C677T and A1298C) potential modulators of a variety of disorders whose development depends on folate/homocysteine imbalance. Here, we provide additional evidence on the protective role of these polymorphisms in acute lymphoblastic leukemia (ALL), the most common pediatric cancer. A case-control study was conducted in 270 ALL patients and 300 healthy controls of French-Canadian origin. The TT677/AA1298 and CC677/CC1298 individuals were associated with reduced risk of ALL (crude odds ratio [OR] = 0.4; 95% confidence interval [CI], 0.2-0.9; and OR = 0.3; 95% CI, 0.1-0.6; respectively). Further stratification in patients born before and after January 1996 (approximate time of Health Canada recommendation for folic acid supplement in pregnancy) revealed that the protective effect of MTHFR variants is accentuated and present only in children born before 1996. Similar results were obtained when a transmission disequilibrium test was performed on a subset of children (n = 95) in a family-based study. This finding suggests gene-environment interaction and its role in the susceptibility to childhood ALL, which is consistent with previous findings associating either folate deficiency or MTHFR polymorphisms with risk of leukemia.

Folic acid deficiency during late gestation decreases progenitor cell proliferation and increases apoptosis in fetal mouse brain

In mice and rats, maternal dietary choline intake during late pregnancy modulates mitosis and apoptosis in progenitor cells of the fetal hippocampus and septum. Because choline and folate are interrelated metabolically, we investigated the effects of maternal dietary folate availability on progenitor cells in fetal mouse telencephalon. Timed-pregnant mice were fed a folate-supplemented (FS), control (FCT) or folate-deficient (FD) AIN-76 diet from d 11-17 of pregnancy. FD decreased the number of progenitor cells undergoing cell replication in the ventricular zones of the developing mouse brain septum (46.6% of FCT), caudate putamen (43.5%), and neocortex (54.4%) as assessed using phosphorylated histone H3 (a specific marker of mitotic phase) and confirmed by bromodeoxyuridine (BrdU) labeling of the S phase. In addition, 106.2% more apoptotic cells were found in FD than in FCT fetal septum. We observed 46.8% more calretinin-positive cells in the medial septal-diagonal band region of FD compared with pups from control dams. FS mice did not differ significantly from FCT mice in any of these measures. These results suggest that progenitor cells in fetal forebrain are sensitive to maternal dietary folate during late gestation.

Multiple single-nucleotide polymorphisms in the methylenetetrahydrofolate reductase and its truncated pseudogene of 23 inbred strains of mice

Reduced 5,10-methylenetetrahydrofolate reductase (MTHFR) results in a number of human diseases. To find a model mouse sensitive to these diseases, we analyzed single-nucleotide polymorphisms (SNPs) of the mouse Mthfr using 23 phylogenetically distant strains of mouse. We found five SNPs: two nonsynonymous and three synonymous. The CAST/Ei strain has the nonsynonymous SNP L350V and five strains (NMRI, KJR, SWN2, MSM, and JF1) have the nonsynonymous SNP S22G. The MTHFR activity of CAST/Ei and MSM showed no significant difference in activity or thermostability compared with that of C57BL/6J. We also found a pseudogene segment of the mouse Mthfr that was not present in human and was more frequently variable than the functional gene. These results suggest a possibility that the truncated pseudogene may buffer variations of the mouse Mthfr functional gene, and the mouse has evolved fewer variations of the gene than human.

Role of polymorphisms in MTHFR and MTHFD1 genes in the outcome of childhood acute lymphoblastic leukemia

The central role of 5,10-methylenetetrahydrofolate reductase (MTHFR) and methylenetetrahydrofolate dehydrogenase (MTHFD1) in folate metabolism renders polymorphisms in genes encoding these enzymes potential modulators of therapeutic response to antifolate chemotherapeutics. The analysis of 201 children treated with methotrexate for childhood acute lymphoblastic leukemia (ALL) showed that patients with either the MTHFR T677A1298 haplotype or MTHFD1 A1958 variant had a lower probability of event-free survival (EFS) in univariate analysis (hazard ratio (HR)=2.2, 95% confidence interval (CI), 1.0-4.7 and 2.8, 95% CI, 1.1-7.3, respectively). Multivariate analysis supported only the role of the MTHFR variant (HR=2.2, 95% CI, 0.9-5.6). However, the association of both genes with ALL outcome appears to be more obvious in the presence of another event-predisposing variant belonging to the same path of drug action. The combined effect of a thymidylate synthase (TS) triple repeat associated with increased TS levels, with either the MTHFR T677A1298 haplotype or MTHFD1 A1958 allele, resulted in a highly significant reduction of EFS (multivariate HR=9.0, 95% CI, 1.9-42.8 and 8.9, 95% CI, 1.8-44.6, respectively). These results reveal the role of gene-gene interactions within a folate pathway, and how they can correlate with relapse probabilities in ALL patients.

Prevalence and Role of Methylenetetrahydrofolate Reductase 677 C→T and 1298 A→C Polymorphisms in Coronary Artery Disease in Arabs

Context.—Previous studies reported an association of 677 C→T and 1298 A→C methylenetetrahydrofolate reductase (MTHFR) variants with coronary artery disease (CAD). No previous studies concerning the prevalence of these 2 MTHFR variants or their possible association with CAD in Arabs are currently available in the literature.

Objective.—To determine the prevalence of MTHFR variants and their potential relevance to CAD among Arabs.

Design.—We used polymerase chain reaction and restriction enzyme digestion to determine the prevalence of these 2 MTHFR polymorphisms in 625 healthy blood donors (BDs) and 545 angiographically confirmed CAD patients of Arab origin.

Results.—For the 677 C→T variant within the CAD group, 64.2% were homozygous wild-type C/C, 32.1% were heterozygous C/T, and 3.7% were homozygous T/T genotype. Within the BD group tested for the 677 C→T variant, 72.2% were homozygous wild-type C/C, 25.8% were heterozygous C/T, and 2% were homozygous T/T genotype. Within the CAD group tested for the 1298 A→C variant (n = 540), 45.7% were homozygous wild-type A/A, 46.9% were heterozygous A/C, and 7.4% were homozygous C/C genotype. Within the BD group tested for the 1298 A→C variant (n = 625), 39.4% were homozygous wild-type A/A, 51.5% were heterozygous A/C, and 9.1% were homozygous C/C genotype. The distribution and allele frequency of these 2 MTHFR variants followed the Hardy-Weinberg equilibrium and were similar in the CAD and BD study groups. The prevalence of the 677 C→T and 1298 A→C compound heterozygosity was 9.6% for the BD group and 12.3% for the CAD group.

Conclusion.—The 2 MTHFR variants tested in this study, individually or compound, are not associated with CAD. Therefore, neither of these 2 variants can be considered an independent risk factor or a predictor for CAD in this population.

Homocysteine-betaine interactions in a murine model of 5,10-methylenetetrahydrofolate reductase deficiency

Hyperhomocysteinemia, a proposed risk factor for cardiovascular disease, is also observed in other common disorders. The most frequent genetic cause of hyperhomocysteinemia is a mutated methylenetetrahydrofolate reductase (MTHFR), predominantly when folate status is impaired. MTHFR synthesizes a major methyl donor for homocysteine remethylation to methionine. We administered the alternate choline-derived methyl donor, betaine, to wild-type mice and to littermates with mild or severe hyperhomocysteinemia due to hetero- or homozygosity for a disruption of the Mthfr gene. On control diets, plasma homocysteine and liver choline metabolite levels were strongly dependent on the Mthfr genotype. Betaine supplementation decreased homocysteine in all three genotypes, restored liver betaine and phosphocholine pools, and prevented severe steatosis in Mthfr-deficient mice. Increasing betaine intake did not further decrease homocysteine. In humans with cardiovascular disease, we found a significant negative correlation between plasma betaine and homocysteine concentrations. Our results emphasize the strong interrelationship between homocysteine, folate, and choline metabolism. Hyperhomocysteinemic Mthfr-compromised mice appear to be much more sensitive to changes of choline/betaine intake than do wild-type animals. Hyperhomocysteinemia, in the range of that associated with folate deficiency or with homozygosity for the 677T MTHFR variant, may be associated with disturbed choline metabolism.

Cardiovascular disease genetics: a long and winding road

PURPOSE OF REVIEW

This review has two major goals. The first goal is to raise some of the methodological problems associated with studying the genetics of complex disorders, specifically cardiovascular diseases. The second is to update the reader with the most recent findings in the area of genotype-phenotype associations as well as the interaction between genetic factors and cardiovascular disease risk markers, with emphasis on those related to lipid metabolism.

RECENT FINDINGS

In terms of new information, three topics are presented: (1) new findings related to classical candidate genes, such as apolipoprotein E, cholesteryl ester transfer protein and hepatic lipase; (2) recent reports related to new loci that have joined the growing list of cardiovascular disease candidate genes (i.e. ATP-binding cassette transporters A1 and C6, peroxisome proliferator activated receptor alpha, interleukin-6); and (3) studies showing that multiple genes appear to be at the intersection of several age-related disorders such as cardiovascular disease, neurological disorders and osteoporosis (i.e. apolipoprotein E, vitamin D receptor, matrix Gla protein, peroxisome proliferator activated receptor gamma, angiotensin-converting enzyme, estrogen receptor, androgen receptor, methylenetetrahydrofolate reductase).

SUMMARY

The dramatic increase in our ability to carry out genotyping is creating a tremendous wealth of information in terms of associations between genetic markers and biochemical or clinical phenotypes. Increased attention, however, should be placed on study design and replication of findings. This should also be facilitated by the inclusion of multiple markers per loci in order to provide a more precise definition of the alleles associated with the phenotypes of interest. Moreover, given the fact that most of the phenotypes are equally affected by genetic and environmental factors, studies should emphasize the analyses of their interaction.

Pharmacokinetics of oral betaine in healthy subjects and patients with homocystinuria

AIMS

Large oral doses of betaine have proved effective in lowering plasma homocysteine in severe hyperhomocysteinaemia. The pharmacokinetic characteristics and metabolism of betaine in humans have not been assessed and drug monitoring for betaine therapy is not available. We studied the pharmacokinetics of betaine and its metabolite dimethylglycine (DMG) in healthy subjects and in three patients with homocystinuria.

METHODS

Twelve male volunteers underwent an open-label study. After one single administration of 50 mg betaine kg-1 body weight and during continuous intake of twice daily 50 mg kg-1 body weight, serial blood samples and 24 h urines were collected to determine betaine and DMG plasma concentrations and urinary excretion, respectively. Patients were evaluated after one single dose of betaine.

RESULTS

We found rapid absorption (t(1/2),abs 00.28 h, s.d. 0.17) and distribution (t(1/2), lambda1 00.59 h, s.d. 0.22) of betaine. A Cmax of 0.94 mmol l-1 (s.d. 0.19) was reached after tmax 00.90 h (s.d. 0.33). The elimination half life t(1/2), z was 14.38 h (s.d. 7.17). After repeated dosage, t(1/2), lambda1 (01.77 h, s.d. 0.75) and t(1/2), z (41.17 h, s.d. 13.50) increased significantly (95% CI 0.73, 01.64 h and 19.90, 33.70 h, respectively), whereas absorption remained unchanged. DMG concentrations increased significantly after betaine administration and accumulation occurred to the same extent as with betaine. Renal clearance was low and urinary excretion of betaine was equivalent to 4% of the ingested dose. Distribution and elimination kinetics in homocystinuric patients appeared to be accelerated.

CONCLUSIONS

Betaine plasma concentrations change rapidly after ingestion. Elimination half-life increased during continuous dosing over 5 days. Betaine is mainly eliminated by metabolism. More pharmacokinetic and pharmacodynamic studies in hyperhomocysteinaemic patients are needed to refine the current treatment with betaine.

Effects of common polymorphisms on the properties of recombinant human methylenetetrahydrofolate reductase

Methylenetetrahydrofolate reductase (MTHFR) catalyzes the conversion of methylenetetrahydrofolate to methyltetrahydrofolate, the major methyl donor for the conversion of homocysteine to methionine. Two common polymorphisms of the human enzyme have been identified: 677C>T, which leads to the substitution of Ala-222 by valine, and 1298A>C, which leads to the replacement of Glu-429 by alanine; the former polymorphism is the most frequent genetic cause of mild hyperhomocysteinemia, a risk factor for cardiovascular disease. By using a baculovirus expression system, recombinant human MTHFR has been expressed at high levels and purified to homogeneity in quantities suitable for biochemical characterization. The Glu429Ala protein has biochemical properties that are indistinguishable from the wild-type enzyme. The Ala222Val MTHFR, however, has an enhanced propensity to dissociate into monomers and to lose its FAD cofactor on dilution; the resulting loss of activity is slowed in the presence of methyltetrahydrofolate or adenosylmethionine. This biochemical phenotype is in good agreement with predictions made on the basis of studies comparing wild-type Escherichia coli MTHFR with a mutant, Ala177Val, homologous to the Ala222Val mutant human enzyme [Guenther, B. D., et al. (1999) Nat. Struct. Biol. 6, 359-365].