The Hordaland Homocysteine Studies

Association between vitamin D deficiency and serum Homocysteine levels and its relationship with coronary artery disease

Homocysteine (Hcy) elevation and vitamin D deficiency have emerged as potential markers of coronary artery disease (CAD). However, even tough hypovitaminosis D has been suggested to interfere with Hcy catabolism, no study has so far addressed the interaction of vitamin D and Hcy and their impact on CAD, that was the aim of present study. A cohort of consecutive patients undergoing coronary angiography in a single center were included and analyzed within the year 2019. Significant CAD was defined as at least 1 vessel stenosis > 50%, while severe CAD as left main and/or three-vessel disease. Hcy and vitamin D levels were assesssed at admission. We included 3150 patients undergoing coronary angiography at our centre, who were divided according to the quartiles values of vitamin D. Patients with lower levels of Vitamin D displayed a higher cardiovascular risk profile and a higher prevalence of CAD. We observed an inverse linear relationship between lower levels of vitamin D and higher Hcy (r = − 0.092, p < 0.001) and a higher prevalence of hyperhomocysteinemia in patients with lower quartiles values of vitamin D (p < 0.001). By forward conditional regression model, low vitamin D appeared as independent predictors of Homocysteine levels above the median (OR[95%CI] = 1.79[1.37–2.33], p < 0.001). In addition, patients with low vitamin D (below the median) and increased Hcy displayed a non-significantly higher rate of CAD (81% vs 77.7%, p = 0.13, adjusted OR[95%CI] = 1.16[0.88–1.54], p = 0.29) but a significant increase in the rate of severe left main/3-vessel CAD (37.4% vs 30.5%, p = 0.005, adjusted OR[95%CI] = 1.29[1.02–1.67], p = 0.04). Among patients with vitamin D levels above the median, Hcy levels did not impact on the prevalence and extent of CAD (77.7 vs 77.2%, p = 0.81, adjusted OR[95%CI] = 0.94[0.73–1.20], p = 0.60 for CAD and 31.8% vs 27.7%, p = 0.08, adjusted OR[95%CI] = 0.97[0.75–1.25], p = 0.81 for severe left main/3-vessel CAD). No significant interaction between Hcy and vitamin D with CAD or severe CAD was observed. The present study shows an independent inverse linear relationship between vitamin D and Hcy values. Moreover, the association of Hcy with the extent of CAD was significant only among patients with hypovitaminosis D, and not in the cohort of subjects with vitamin D levels above the median, suggesting that a normal vitamin D status can prevent the deleterious effects of hyperhomocysteinemia on coronary atherosclerosis, a hypothesis that certainly needs further confirmation in larger randomized trials.

Effects of Alzheimer-Like Pathology on Homocysteine and Homocysteic Acid Levels-An Exploratory In Vivo Kinetic Study

Hyperhomocysteinemia has been suggested potentially to contribute to a variety of pathologies, such as Alzheimer’s disease (AD). While the impact of hyperhomocysteinemia on AD has been investigated extensively, there are scarce data on the effect of AD on hyperhomocysteinemia. The aim of this in vivo study was to investigate the kinetics of homocysteine (HCys) and homocysteic acid (HCA) and effects of AD-like pathology on the endogenous levels. The mice received a B-vitamin deficient diet for eight weeks, followed by the return to a balanced control diet for another eight weeks. Serum, urine, and brain tissues of App^NL-G-F knock-in and C57BL/6J wild type mice were analyzed for HCys and HCA using LC-MS/MS methods. Hyperhomocysteinemic levels were found in wild type and knock-in mice due to the consumption of the deficient diet for eight weeks, followed by a rapid normalization of the levels after the return to control chow. Hyperhomocysteinemic App^NL-G-F mice had significantly higher HCys in all matrices, but not HCA, compared to wild type control. Higher serum concentrations were associated with elevated levels in both the brain and in urine. Our findings confirm a significant impact of AD-like pathology on hyperhomocysteinemia in the App^NL-G-F mouse model. The immediate normalization of HCys and HCA after the supply of B-vitamins strengthens the idea of a B-vitamin intervention as a potentially preventive treatment option for HCys-related disorders such as AD.

Impact of Hyperhomocysteinemia and Different Dietary Interventions on Cognitive Performance in a Knock-in Mouse Model for Alzheimer's Disease

BACKGROUND

Hyperhomocysteinemia is considered a possible contributor to the complex pathology of Alzheimer's disease (AD). For years, researchers in this field have discussed the apparent detrimental effects of the endogenous amino acid homocysteine in the brain. In this study, the roles of hyperhomocysteinemia driven by vitamin B deficiency, as well as potentially beneficial dietary interventions, were investigated in the novel App^NL-G-F knock-in mouse model for AD, simulating an early stage of the disease.

METHODS

Urine and serum samples were analyzed using a validated LC-MS/MS method and the impact of different experimental diets on cognitive performance was studied in a comprehensive behavioral test battery. Finally, we analyzed brain samples immunohistochemically in order to assess amyloid-β (Aβ) plaque deposition.

RESULTS

Behavioral testing data indicated subtle cognitive deficits in App^NL-G-F compared to C57BL/6J wild type mice. Elevation of homocysteine and homocysteic acid, as well as counteracting dietary interventions, mostly did not result in significant effects on learning and memory performance, nor in a modified Aβ plaque deposition in 35-week-old App^NL-G-F mice.

CONCLUSION

Despite prominent Aβ plaque deposition, the App^NL-G-F model merely displays a very mild AD-like phenotype at the investigated age. Older App^NL-G-F mice should be tested in order to further investigate potential effects of hyperhomocysteinemia and dietary interventions.

Association of dietary vitamin K and risk of coronary heart disease in middle-age adults: the Hordaland Health Study Cohort

OBJECTIVE

The role of vitamin K in the regulation of vascular calcification is established. However, the association of dietary vitamins K1 and K2 with risk of coronary heart disease (CHD) is inconclusive.

DESIGN

Prospective cohort study.

SETTING

We followed participants in the community-based Hordaland Health Study from 1997 - 1999 through 2009 to evaluate associations between intake of vitamin K and incident (new onset) CHD. Baseline diet was assessed by a past-year food frequency questionnaire. Energy-adjusted residuals of vitamin K1 and vitamin K2 intakes were categorised into quartiles.

PARTICIPANTS

2987 Norwegian men and women, age 46-49 years.

METHODS

Information on incident CHD events was obtained from the nationwide Cardiovascular Disease in Norway (CVDNOR) Project. Multivariable Cox regression estimated HRs and 95% CIs with test for linear trends across quartiles. Analyses were adjusted for age, sex, total energy intake, physical activity, smoking and education. A third model further adjusted K1 intake for energy-adjusted fibre and folate, while K2 intake was adjusted for energy-adjusted saturated fatty acids and calcium.

RESULTS

During a median follow-up time of 11 years, we documented 112 incident CHD cases. In the adjusted analyses, there was no association between intake of vitamin K1 and CHD (HRQ4vsQ1 = 0.92 (95% CI 0.54 to 1.57), p for trend 0.64), while there was a lower risk of CHD associated with higher intake of energy-adjusted vitamin K2 (HRQ4vsQ1 = 0.52 (0.29 to 0.94), p for trend 0.03). Further adjustment for potential dietary confounders did not materially change the association for K1, while the association for K2 was slightly attenuated (HRQ4vsQ1 = 0.58 (0.28 to 1.19)).

CONCLUSIONS

A higher intake of vitamin K2 was associated with lower risk of CHD, while there was no association between intake of vitamin K1 and CHD.

TRIAL REGISTRATION NUMBER

NCT03013725.

Which Aspects of Positive Affect Are Related to Mortality? Results From a General Population Longitudinal Study

Background

Previous research has shown a link between low positive affect and mortality, but questions remain about how positive affect is related to mortality and how this differs by gender and age.

Purpose

To investigate the relationships between positive affect, negative affect, and mortality in a general population sample, and to examine whether these relationships were related to age, sex, or cause-specific mortality.

Methods

We used data from 5,554 Norwegian participants aged 47-49 and 71-74 years who completed the Positive and Negative Affect Schedule (PANAS) and also provided data on demographics, health behaviors, and physical health as part of the Hordaland Health Study. The primary outcome was mortality after an average follow-up period of 16.5 years.

Results

Participants in the lowest positive affect tertile had a near twofold increased mortality risk, compared to those in the highest positive affect tertile. This association was driven primarily by the PANAS "active" item and persisted, even after controlling for activity-related confounds and other positive affect items. No significant associations were found between negative affect and mortality. The relationship between positive affect and mortality was not significantly attenuated by age or sex. Although low positive affect was associated with an increased risk of mortality, it was not related to a specific cause of death.

Conclusions

Low positive affect was significantly associated with mortality risk. The relationship was driven by the PANAS active item and not associated with cause-specific mortality. Findings suggest future research should examine the association between feeling inactive, sedentary behavior, and subsequent mortality.

Nitration-mediated deficiency of cystathionine β-synthase activity accelerates the progression of hyperhomocysteinemia

Deficiency of cystathionine β-synthase (CBS) activity is the most common cause of increased homocysteine (Hcy). However, until now the underlying mechanisms why CBS activity decreased still remain unresolved. The goal of this study was to explore the contribution of nitrative stress to deficiency of CBS activity, and further identify the possible nitration sites of CBS protein. Results showed that in elderly people, there was an increased nitrative stress level, which was relative to elevated Hcy level. In natural aging rats and diet-induced hyperhomocysteinemia (HHcy) rats, the levels of Hcy and nitrative stress were both elevated, and interestingly, pretreatment with peroxynitrite (ONOO^-) scavenger FeTMPyP ameliorated the elevation of Hcy as well as nitrative stress. Further experiments showed the reduction of CBS bioactivity and elevation of CBS nitration in two rats models were both reversed by FeTMPyP pretreatment. In vitro, replacement of tyrosine (Tyr, Y) residue (Tyr¹⁶³, Tyr²²³, Tyr³⁸¹, Tyr⁵¹⁸) in CBS with alanine (Ala, A) abolished the Hcy-mediated CBS inactivation. These results highlighted that deficiency of CBS activity was correlated with the nitration of CBS at Tyr¹⁶³, Tyr²²³, Tyr³⁸¹ and Tyr⁵¹⁸, which may play a mutual role in the progression of HHcy. This discovery may shed a novel light on the pathogenesis of HHcy and provide a possible gene therapy target to HHcy.

A hybrid stochastic model of folate-mediated one-carbon metabolism: Effect of the common C677T MTHFR variant on de novo thymidylate biosynthesis

Folate-mediated one-carbon metabolism (FOCM) is an interconnected network of metabolic pathways, including those required for the de novo synthesis of dTMP and purine nucleotides and for remethylation of homocysteine to methionine. Mouse models of folate-responsive neural tube defects (NTDs) indicate that impaired de novo thymidylate (dTMP) synthesis through changes in SHMT expression is causative in folate-responsive NTDs. We have created a hybrid computational model comprised of ordinary differential equations and stochastic simulation. We investigated whether the de novo dTMP synthesis pathway was sensitive to perturbations in FOCM that are known to be associated with human NTDs. This computational model shows that de novo dTMP synthesis is highly sensitive to the common MTHFR C677T polymorphism and that the effect of the polymorphism on FOCM is greater in folate deficiency. Computational simulations indicate that the MTHFR C677T polymorphism and folate deficiency interact to increase the stochastic behavior of the FOCM network, with the greatest instability observed for reactions catalyzed by serine hydroxymethyltransferase (SHMT). Furthermore, we show that de novo dTMP synthesis does not occur in the cytosol at rates sufficient for DNA replication, supporting empirical data indicating that impaired nuclear de novo dTMP synthesis results in uracil misincorporation into DNA.

Active recruitment and limited participant-load related to high participation in large population-based biobank studies

OBJECTIVES

Insight into baseline participation rates and their determinants is crucial for designing future population-based biobank studies. We therefore conducted a systematic review and meta-analysis of baseline participation rates and their determinants in large longitudinal population-based biobank studies.

STUDY DESIGN AND SETTING

We screened studies registered within the Public Population Project in Genomics and Society and in the Biobanking and Biomolecular Resources Research Infrastructure catalogues to find potentially eligible studies. We retrieved data with regard to participation rate, biobank design, performed measurements, and specific strategies for improving participation. We calculated weighted pooled proportions for each determinant using random-effects models.

RESULTS

We included 25 studies (participation rates 5-96%). Participation rates were highest for studies involving face-to-face recruitment [82.6%; 95% confidence interval (CI): 72.2%, 90.9%], for studies in which participants were visited for an examination (77.5%; 95% CI: 64.0%, 88.6%) and for studies in which at maximum four measurements were performed (78.2%; 95% CI: 69.7%, 85.7%). Specific strategies to improve participation were not found to be associated with higher participation rates.

CONCLUSION

Specific choices of recruitment methods and design have consequences for participation rates. These insights may help to increase participation in future studies, thereby enhancing the validity of their findings.

Interactions between plasma concentrations of folate and markers of vitamin B(12) status with cognitive performance in elderly people not exposed to folic acid fortification: the Hordaland Health Study

A combination of high folate with low vitamin B12 plasma status has been associated with cognitive impairment in a population exposed to mandatory folic acid fortification. The objective of the present study was to examine the interactions between plasma concentrations of folate and vitamin B12 markers in relation to cognitive performance in Norwegian elderly who were unexposed to mandatory or voluntary folic acid fortification. Cognitive performance was assessed by six cognitive tests in 2203 individuals aged 72-74 years. A combined score was calculated using principal component analysis. The associations of folate concentrations, vitamin B12 markers (total vitamin B12, holotranscobalamin (holoTC) and methylmalonic acid (MMA)) and their interactions in relation to cognitive performance were evaluated by quantile regression and least-squares regression, adjusted for sex, education, apo-ɛ4 genotype, history of CVD/hypertension and creatinine. Cross-sectional analyses revealed an interaction (P= 0·009) between plasma concentrations of folate and vitamin B12 in relation to cognitive performance. Plasma vitamin B12 concentrations in the lowest quartile ( < 274 pmol/l) combined with plasma folate concentrations in the highest quartile (>18·5 nmol/l) were associated with a reduced risk of cognitive impairment compared with plasma concentrations in the middle quartiles of both vitamins (OR 0·22, 95 % CI 0·05, 0·92). The interaction between folate and holoTC or MMA in relation to cognitive performance was not significant. In conclusion, this large study population unexposed to mandatory folic acid fortification showed that plasma folate, but not plasma vitamin B12, was associated with cognitive performance. Among the elderly participants with vitamin B12 concentrations in the lower range, the association between plasma folate and cognitive performance was strongest.

Big-endothelin 1 (big ET-1) and homocysteine in the serum of dogs with chronic kidney disease

This study was aimed at determining the serum concentration of homocysteine (Hcy) and big endothelin-1 (big ET-1, the precursor of endothelin) in dogs with chronic kidney disease (CKD) with and without hypertension, proteinuria and inflammation, in order to explore their role as biomarkers of hypertension associated with CKD. Hcy and big ET-1 were measured using an enzyme-linked immunosorbent assay and an enzymatic cyclic reaction, respectively, in dogs with CKD staged, as proposed by the International Renal Interest Society (IRIS), using serum creatinine, urinary protein to creatinine (UPC) ratio and systolic blood pressure, and classified as affected or not by inflammation based on the serum concentration of C-reactive protein (CRP). Serum Hcy was significantly higher in dogs of IRIS stages II, III and IV compared with controls and in proteinuric compared with non-proteinuric dogs. No differences relating to the degree of hypertension or to the CRP concentration were found. Serum big ET-1 significantly increased in dogs of IRIS stage IV compared with controls, in proteinuric compared with non-proteinuric dogs, in dogs with severe hypertension compared with those without hypertension, and in dogs with increased CRP compared to those with normal CRP concentrations. Hcy only correlated with serum creatinine but big ET-1 significantly correlated with serum creatinine, UPC ratio, systolic blood pressure, and increased CRP. In conclusion, both Hcy and big ET-1 increase in dogs with CKD. Although further research is needed, big ET-1, but not Hcy, may also be considered as a biomarker of hypertension.

Increased homocysteine, homocysteine-thiolactone, protein homocysteinylation and oxidative stress in the circulation of patients with Eales' disease

BACKGROUND

Eales' disease (ED) is an idiopathic retinal vascular disorder. It presents with inflammation and neovascularization in the retina. Adult men, aged between 15 and 40 years are more susceptible than women. Homocysteine has been implicated in other ocular diseases including age-related macular degeneration (ARMD), central retinal vein occlusion (CRVO) and optic neuropathy. The present study investigates the role of homocysteine in ED.

METHODS

Forty male subjects, 20 with ED and 20 healthy controls, were recruited to the study. Their blood samples were used to measure thiobarbituric acid reactive substances (TBARS), glutathione (GSH), homocysteine, homocysteine-thiolactone, extent of homocysteine conjugation with proteins and plasma copper concentration.

RESULTS

In the ED group, plasma homocysteine (18.6 ± 1.77 µmol/L, P < 0.001) and homocysteine-thiolactone (45.3 ± 6.8 nmol/L, P < 0.0001) concentrations were significantly higher compared to homocysteine (11.2 ± 0.64 µmol/L) and homocysteine-thiolactone (7.1 ± 0.94 nmol/L) concentrations in control subjects. TBARS (P < 0.011) and protein homocysteinylation (P < 0.030) were higher in the ED group while GSH (5.9 ± 0.44 µmol/L, P < 0.01) and copper (6.6 ± 0.42 µmol/L, P < 0.001) were lower compared to GSH (8.1 ± 0.41 µmol/L) and copper (15.4 ± 0.73 µmol/L) concentrations in control subjects.

CONCLUSIONS

Increased homocysteine, and its metabolite thiolactone, is associated with the functional impairment of protein due to homocysteinylation in ED.

Cystathionine β-synthase deficiency causes infertility by impairing decidualization and gene expression networks in uterus implantation sites

Hyperhomocysteinemia has been reported in human reproduction as a risk factor for early pregnancy loss, preeclampsia, and congenital birth defects like spina bifida. Female infertility was also observed in cystathionine beta synthase-deficient mice ( Cbs-KO) as an animal model for severe hyperhomocysteinemia. The aim for the present research was to elucidate the time-point of pregnancy loss and to pinpoint gene and cellular changes involved in the underlying pathological mechanism. By mating 90-day-old wild-type and Cbs-KO female mice with their homologous male partners, we found that pregnancy loss in Cbs-KO occurred between the 8th and 12th gestation day during placenta formation. DNA microarrays were carried out on uterus from implantation and interimplantation samples obtained on day 8. The results allowed us to select genes potentially involved in embryo death; these were individually confirmed by RT-qPCR, and their expressions were also followed throughout pregnancy. We found that changes in expression of Calb1, Ttr, Expi, Inmt, Spink3, Rpgrip1, Krt15, Mt-4, Gzmc, Gzmb, Tdo2, and Afp were important for pregnancy success, since a different regulation in Cbs-KO mice was found. Also, differences in relationships among selected genes were observed, indicating a dysregulation of these genes in Cbs-KO females. In conclusion, our data provide more information on the gene expression cascade and its timely regulated process required for a successful pregnancy. In addition, we unveil new potential avenues to explore further investigations in pregnancy loss.

The role of homocysteine and methylenetetrahydrofolate reductase, methionine synthase, methionine synthase reductase polymorphisms in the development of cardiovascular diseases and hypertension

Cardiovascular diseases (CVDs) are the leading causes of death in the developed countries. Elevated homocysteine level is as an independent risk factor of CVDs. The C677T and A1298C variants of methylenetetrahydrofolate reductase gene (MTHFR) have been shown to influence folate and homocysteine metabolisms. However, the relationship between MTHFR polymorphisms and hyperhomocysteinemia has not been well established yet. The gene variants were also reported to be associated with CVDs. In addition, the C677T polymorphisms may play a role in the development of hypertension. Recent research evidence has suggested that MTHFR variants might be independently linked to CVDs and hypertension, because of the involvement of the MTHFR enzyme product (5-methyl-tetrahydrofolate /5-MTHF) in the regulation of endothelial functions. Further research is required to investigate the association between gene polymorphisms of folate-metabolizing enzymes and CVDs, and to identify the possible role of the relevant gene variants in the molecular pathogenesis of hyperhomocysteinemia. Orv. Hetil., 2012, 153, 445–453.

Vascular complications of cystathionine β-synthase deficiency: future directions for homocysteine-to-hydrogen sulfide research

Homocysteine (Hcy), a cardiovascular and neurovascular disease risk factor, is converted to hydrogen sulfide (H(2)S) through the transsulfuration pathway. H(2)S has attracted considerable attention in recent years for many positive effects on vascular health and homeostasis. Cystathionine β-synthase (CBS) is the first, and rate-limiting, enzyme in the transsulfuration pathway. Mutations in the CBS gene decrease enzymatic activity, which increases the plasma Hcy concentration, a condition called hyperhomocysteinemia (HHcy). Animal models of CBS deficiency have provided invaluable insights into the pathological effects of transsulfuration impairment and of both mild and severe HHcy. However, studies have also highlighted the complexity of HHcy and the need to explore the specific details of Hcy metabolism in addition to Hcy levels per se. There has been a relative paucity of work addressing the dysfunctional H(2)S production in CBS deficiency that may contribute to, or even create, HHcy-associated pathologies. Experiments using CBS knockout mice, both homozygous (-/-) and heterozygous (+/-), have provided 15 years of new knowledge and are the focus of this review. These murine models present the opportunity to study a specific mechanism for HHcy that matches one of the etiologies in many human patients. Therefore, the goal of this review was to integrate and highlight the critical information gained thus far from models of CBS deficiency and draw attention to critical gaps in knowledge, with particular emphasis on the modulation of H(2)S metabolism. We include findings from human and animal studies to identify important opportunities for future investigation that should be aimed at generating new basic and clinical understanding of the role of CBS and transsulfuration in cardiovascular and neurovascular disease.

A community based study of the relationship between homocysteine and some of the life style factors

Till date no community based data on plasma homocysteine is available in North Eastern Region. Hence, the present study was conducted to analyze and correlate the plasma homocysteine level with some life style factors like diet, alcohol intake, smoking habit and body weight, in a cross-section of population. 12 h fasting samples of 970 apparently healthy, Assamese population of both genders in the age group of 35-86 years, mostly from the urban area of Assam were tested for plasma total homocysteine level over a period of 3 years. Out of 970 volunteers, hyperhomocysteinemia was detected in 533 (55%) individuals with a mean value of 18.41 μmol/l. Of that hyperhomocysteinemia, 89.1% were in the range of moderately high and rest 10.9% were intermediate high. Another finding was that males had a tendency towards greater value (mean = 20.36 μmol/l) than females (mean = 16.37 μmol/l). It was observed that the relationship of homocysteine levels to gender and some of the life style factors were also significant.

Choline in anxiety and depression: the Hordaland Health Study

BACKGROUND

Despite its importance in the central nervous system as a precursor for acetylcholine and membrane phosphatidylcholine, the role of choline in mental illness has been little studied.

OBJECTIVE

We examined the cross-sectional association between plasma choline concentrations and scores of anxiety and depression symptoms in a general population sample.

DESIGN

We studied a subsample (n = 5918) of the Hordaland Health Study, including both sexes and 2 age groups of 46-49 and 70-74 y who had valid information on plasma choline concentrations and symptoms of anxiety and depression measured by the Hospital Anxiety and Depression Scale--the latter 2 as continuous measures and dichotomized at a score > or =8 for both subscales.

RESULTS

The lowest choline quintile was significantly associated with high anxiety levels (odds ratio: 1.33; 95% CI: 1.06, 1.69) in the fully adjusted (age group, sex, time since last meal, educational level, and smoking habits) logistic regression model. Also, the trend test in the anxiety model was significant (P = 0.007). In the equivalent fully adjusted linear regression model, a significant inverse association was found between choline quintiles and anxiety levels (standardized regression coefficient = -0.027, P = 0.045). We found no significant associations in the corresponding analyses of the relation between plasma choline and depression symptoms.

CONCLUSION

In this large population-based study, choline concentrations were negatively associated with anxiety symptoms but not with depression symptoms.

Homocysteine level and coronary heart disease incidence: a systematic review and meta-analysis

OBJECTIVE

To determine whether an elevated homocysteine level is an independent risk factor for the development of coronary heart disease (CHD) to aid the US Preventive Services Task Force in its evaluation of novel risk factors for incident CHD.

METHODS

Studies of homocysteine and CHD were identified by searching MEDLINE (1966 through March 2006). We obtained additional articles by reviewing reference lists from prior reviews, original studies, editorials, and Web sites and by consulting experts. We included prospective cohort studies that measured homocysteine and Framingham risk factors and the incidence of CHD in the general adult population without known CHD. Each study was quality rated using criteria developed by the US Preventive Services Task Force. We conducted a meta-analysis using a random-effects model to determine summary estimates of the risk of major CHD associated with each 5-micromol/L increase in homocysteine level. The systematic review and meta-analysis were conducted between January 25, 2005, and September 17, 2007.

RESULTS

We identified 26 articles of good or fair quality. Most studies found elevations of 20% to 50% in CHD risk for each increase of 5 micromol/L in homocysteine level. Meta-analysis yielded a combined risk ratio for coronary events of 1.18 (95% confidence interval, 1.10-1.26) for each increase of 5 micromol/L in homocysteine level. The association between homocysteine and CHD was similar when analyzed by sex, length of follow-up, outcome, study quality, and study design.

CONCLUSION

Each increase of 5 micromol/L in homocysteine level increases the risk of CHD events by approximately 20%, independently of traditional CHD risk factors.

Homocysteine Measurement by an Enzymatic Method and Potential Role of Homocysteine as a Biomarker in Dogs

In humans, homocysteine (Hcy) is employed to monitor renal, cardiovascular, and other diseases and their complications. The aim of the current study was to define the analytical performances of an enzymatic method not yet validated in dogs for measuring homocysteine, and to assess the possible clinical usefulness of Hcy measurement. Using conventional approaches, the analytical performances were investigated by assessing, imprecision, inaccuracy, and interference of hemoglobin, triglycerides, and bilirubin. The possible clinical usefulness of Hcy determination was assessed by comparing the results of healthy dogs ( n = 8) with those of dogs with heart disease ( n = 10), inflammation ( n = 6), gastrointestinal disorders ( n = 7), neoplasia ( n = 8), renal failure ( n = 4), trauma ( n = 7), and other miscellaneous diseases ( n = 6). Preliminary evaluation of this enzymatic method showed it to be precise at Hcy levels close to or higher than the values in dogs with renal or cardiac disorders that had the highest Hcy levels. By contrast, at low Hcy levels, which were recorded basically in control dogs, the method suffers from high imprecision. The sample of choice is serum. The use of icteric samples should be avoided, while hemoglobin and lipids have only a minor effect on Hcy measurement. In conclusion, the enzymatic method employed in the current study provides useful information in dogs and could be used to monitor cardiac and renal disorders, in which Hcy concentrations are elevated.

General anesthesia and methylenetetrahydrofolate reductase deficiency

Methylenetetrahydrofolate reductase (MTHFR) deficiency is an autosomal recessive disorder with a spectrum of manifestations including neurological symptoms, premature arteriosclerosis, and venous and arterial thrombosis. Most patients are heterozygous for multiple MTHFR substitutions; small minorities are homozygous for mutations at this locus. Among these mutations, the C677T polymorphism is the most deleterious. Nitrous oxide use in anesthesia leads to significant increases in plasma homocysteine. We present a patient undergoing urgent surgery with a preoperative diagnosis of homozygous MTHFR deficiency.

Daily variations of homocysteine concentration may influence methylation of DNA in normal healthy individuals

The regulation of genetic expression is tightly controlled and well balanced in the organism by different epigenetic mechanisms such as DNA methylation and histone modifications. DNA methylation occurring after embryogenesis is seen mainly as an irreversible event. Even small changes in genomic DNA methylation might be of biological relevance, and several factors influencing DNA methylation have been identified so far, one being homocysteine. In this study, genomic DNA methylation was analyzed and homocysteine plasma levels were measured over a 24 h period in 30 healthy students (15 males and 15 females) exposed to a standard 24 h regime of daytime activity alternating with nighttime sleep. Plasma homocysteine concentrations were measured using HPLC detection. DNA was extracted from whole EDTA blood, and genomic DNA methylation was assessed by fluorescently labeled cytosine extension assay. Both homocysteine and DNA methylation showed 24 h variation. Homocysteine showed a significant daily rhythm with an evening peak and nocturnal nadir in all subjects (p<0.001). Males showed higher overall homocysteine levels compared to females (p=0.002). Genomic DNA methylation showed a significant rhythm with increased levels at night (p=0.021), which was inverse to plasma homocysteine levels.

Cystathionine beta synthase participates in murine oocyte maturation mediated by homocysteine

Our previous study demonstrated that cystathionine beta synthase (CBS) is highly expressed in the cumulus-oocyte complex during ovulation. However, the role of CBS during oocyte maturation remains uncertain. In this study, a small-interfering (si) RNA interference (siRNA) approach was used to investigate the potential role of CBS during oocyte maturation. Accompanied with a gradual increase of homocysteine, the introduction of CBS-siRNA into murine granulosa cells selectively depleted the corresponding target mRNA and protein for CBS as assessed by semi-quantitative reverse-transcriptase PCR (RT-PCR) and immunofluorescence staining. When fully grown, germinal vesicle (GV) oocytes matured in vitro for 16 h using medium from transfected granulosa cells, the functional suppression of CBS resulted in a significant increase in the rate of GV-arrested oocytes. The results of this study provide evidence that CBS participates in the process of oocyte maturation. Furthermore, this effect may be fulfilled by conditioning the level of homocysteine in the microenvironment of the oocyte.

Homocysteine, brain natriuretic peptide and chronic heart failure: a critical review

Chronic heart failure (CHF) is a major public health problem causing considerable morbidity and mortality. Recently, plasma homocysteine (HCY) has been suggested to be significantly increased in CHF patients. This article reviews the relation between hyperhomocysteinemia (HHCY) and CHF. Clinical data indicate that HHCY is associated with an increased incidence, as well as severity, of CHF. In addition, HCY correlates with brain natriuretic peptide (BNP), a modern biochemical marker of CHF, which is used for diagnosis, treatment guidance and risk assessment. Animal studies showed that experimental HHCY induces systolic and diastolic dysfunction, as well as an increased BNP expression. Moreover, hyperhomocysteinemic animals exhibit an adverse cardiac remodeling characterized by accumulation of interstitial and perivascular collagen. In vitro superfusion experiments with increasing concentrations of HCY in the superfusion medium stimulated myocardial BNP release independent from myocardial wall stress. Thus, clinical and experimental data underline a correlation between HHCY and BNP supporting the role of HHCY as a causal factor for CHF. The mechanisms leading from an elevated HCY level to reduced pump function and adverse cardiac remodeling are a matter of speculation. Existing data indicate that direct effects of HCY on the myocardium, as well as nitric oxide independent vascular effects, are involved. Preliminary data from small intervention trials have initiated the speculation that HCY lowering therapy by micronutrients may improve clinical as well as laboratory markers of CHF.

In conclusion, HHCY might be a potential etiological factor in CHF. Future studies need to explore the pathomechanisms of HHCY in CHF. Moreover, larger intervention trials are needed to clarify whether modification of plasma HCY by B-vitamin supplementation improves the clinical outcome in CHF patients.

Clin Chem Lab Med 2007;45:1633–44.

A review of homocysteine and heart failure

Chronic heart failure (CHF) is a major public health problem causing considerable morbidity and mortality. Recently, plasma homocysteine (HCY) has been suggested to be increased in CHF patients potentially representing a newly recognized risk marker. This manuscript reviews the existing literature regarding hyperhomocysteinemia (HHCY) and CHF. Clinical data indicate that HHCY is associated with an increased incidence of CHF as well as with the severity of the disease. Mechanistic studies of HHCY and CHF are rare. However, preliminary results suggest that HHCY causes adverse cardiac remodelling characterized by interstitial and perivascular fibrosis resulting in increased myocardial stiffness. In addition, HHCY seems to affect the pump function of the myocardium. The mechanisms leading from an elevated HCY level to reduced pump function and adverse cardiac remodelling are a matter of speculation. Existing data indicate that direct effects of HCY on the myocardium as well as NO independent vascular effects are involved. In conclusion, HHCY might be a potential aetiological factor in CHF. Future studies need to clarify the mechanistic role of HHCY in CHF as a useful paradigm with most interesting therapeutic implications, because HCY lowering therapy could favourably influence the prognosis in CHF patients.

Cystathionine β-synthase is essential for female reproductive function

In human reproduction, hyperhomocysteinemia has been reported as a risk factor for early pregnancy loss and congenital birth defects. Hyperhomocysteinemia is also recognized as a cause of maternal obstetric complications such as preeclampsia. The role of plasma hyperhomocysteinemia in female fertility was examined using cystathionine beta synthase knockout (cbs KO) mice. Cbs KO females were infertile, showed alterations in the estrus cycle and an increased progesterone response during pseudo-pregnancy induction. Both cbs KO ovaries and ovulated oocytes showed no major morphological alterations. However, placental and uterine masses were decreased at day 18 of pregnancy and showed morphological abnormalities. In cbs-KO pregnant females, the number of uterine implantation sites was not decreased despite the low number of surviving embryos. Fertility was restored when cbs-deficient ovaries were transplanted to normal ovarectomized recipients. We detected an increased uterine expression of Grp78, a marker of endoplasmic reticulum stress, which was accompanied by the decreased levels of uterine cbs mRNA in both hyperhomocysteinemic heterozygous (fertile) and homozygous (non-fertile) females. Our results indicate that cbs -/- female infertility is a consequence of the uterine failure and demonstrate that uterine endoplasmic reticulum stress and cbs expression are not determinant of infertility, suggesting that uterine dysfunction is a consequence of either hyperhomocysteinemia or other factor(s) in the uterine environment of cbs -/- animals. In summary, these studies demonstrate the potential importance of homocysteine levels for uterine handling of embryos.

Total plasma homocysteine values among elderly subjects: findings from the Maracaibo Aging Study

OBJECTIVES

The present study generated baseline data for total homocysteine (tHcy) in elderly Caribbeans of Hispanic ancestry, residing in Venezuela, their country of origin.

DESIGN AND METHODS

2106 participants in the Maracaibo Aging Study (MAS), older than 55 years, underwent standardized clinical and laboratory assessments, including measurement of plasma tHcy levels, folate, and vitamin B12 in fasting samples.

RESULTS

tHcy concentration in the healthy, normative group ranged from 4.1 to 31.8 micromol/L, with a median of 11.5+/-4.7 micromol/L. tHcy level increased with age, was significantly higher in men than in women, and exhibited inverse correlations with folate and vitamin B12.

CONCLUSIONS

tHcy levels of the MAS participants were generally higher than levels previously reported for community-dwelling elderly populations from other countries. The normative centile curves for tHcy can be used in disease risk analysis for this population, and possibly for other Hispanic populations residing in the Caribbean.

The Hordaland Homocysteine Study: a community-based study of homocysteine, its determinants, and associations with disease

The Hordaland Homocysteine Study (HHS) is a population-based study of more than 18,000 men and women in the county of Hordaland in Western Norway. The first investigation (HHS-I) took place in 1992-93, when the subjects were aged 40-67 y. In 1997-99, a follow-up study (HHS-II) of 7,053 subjects was carried out. In this large population, plasma levels of total homocysteine (tHcy) are associated with several physiologic and lifestyle factors and common diseases. Increasing age, male sex, smoking, coffee consumption, high blood pressure, unfavorable lipid profile, high creatinine, and the MTHFR 677C > T polymorphism are among the factors associated with increased tHcy levels; physical activity, moderate alcohol consumption, and a good folate or vitamin B-12 status are associated with lower tHcy levels. Subjects with raised tHcy levels have increased risk of cardiovascular morbidity, cardiovascular and noncardiovascular mortality, and are more likely to suffer from depression and from cognitive deficit (elderly). Among women, raised tHcy levels are associated with decreased bone mineral density and increased risk of osteoporosis. Women with raised tHcy levels also have an increased risk of having suffered from pregnancy complications and an adverse pregnancy outcome. Significant associations between tHcy and clinical outcomes are usually observed for tHcy levels > 15 micromol/L, but for most conditions, there is a continuous concentration-response relation with no apparent threshold concentration. Overall, the findings from HHS indicate that a raised tHcy level is associated with multiple clinical conditions, whereas a low tHcy level is associated with better physical and mental health.

Dietary and other lifestyle correlates of serum folate concentrations in a healthy adult population in Crete, Greece: a cross-sectional study

Background

Folate has emerged as a key nutrient for optimising health. Impaired folate status has been identified as a risk factor for cardiovascular disease, various types of cancers, and neurocognitive disorders. The study aimed at examining the distribution and determinants of serum folate concentrations in a healthy adult population in Crete, Greece.

Methods

A cross-sectional sample of 486 healthy adults (250 men, 236 women) aged 39 ± 14 years, personnel of the Medical School and the University Hospital of Crete in Greece, was examined. Serum folate and vitamin B₁₂ concentrations were measured by microbiological assay, and total homocysteine was determined fluorometrically and by high-pressure liquid chromatography. Lifestyle questionnaires were completed, and nutrient intakes and food consumption were assessed by 24-h dietary recalls. Multivariate analyses were performed using SPSS v10.1.

Results

The geometric mean (95% confidence interval) concentrations of serum folate were 15.6 μmol/l (14.6–16.8) in men and 19.2 μmol/l (17.9–20.7) in women (p < 0.001). Inadequate folate levels (≤7 nmol/l) were present in 6.8% of men and 2.1% of women (p < 0.001). Approximately 76% of men and 87% of women did not meet the reference dietary intake for folate (400 μg/day). Serum folate was inversely related to total homocysteine levels (p < 0.001). Increased tobacco and coffee consumption were associated with lower folate concentrations (p < 0.05 for both) but these associations disappeared after controlling for nutrient intakes. In multivariate analysis, intakes of MUFA, fibre, calcium, magnesium, folate, and vitamins A, E, C, B₁, and B₆ were positively associated with serum folate. Consumption of potatoes, legumes, fruits, and vegetables were favourably related to the serum folate status.

Conclusion

Serum folate concentrations were associated with various demographic, lifestyle and dietary factors in healthy Cretan adults. Large-scale epidemiological studies should be conducted within the general Greek adult population to assess the prevalence of impaired folate status and further examine associations with dietary patterns and chronic disease risk. Considering the importance of folate in health maintenance, it is important to increase the public's awareness of modifiable lifestyle patterns and diet and tobacco use in particular, which may be associated with improved folate status.

Plasma total homocysteine and memory in the elderly: the Hordaland Homocysteine Study

We examined the relation between plasma total homocysteine (tHcy), folate, vitamin B12, and episodic memory in elderly community-dwelling subjects. A population-based study was conducted in 1992 and 1993, and subjects were re-investigated after 6 years. Plasma analytes were determined on both occasions. At follow-up, memory performance, using the Kendrick Object Learning Test, was investigated in 2,189 subjects (age, 65-67 years at baseline). Subjects with memory deficit (test score, < 25) had higher tHcy and lower folate at follow-up compared with those without memory deficit: 12.6 (95% confidence interval [CI], 12.1, 13.1) versus 11.5 (95% CI, 11.3, 11.6) micromol/L (p < 0.001) for tHcy, and 6.7 (95% CI, 6.2, 7.1) versus 7.6 (95% CI, 7.5, 7.8) nmol/L (p < 0.001) for folate. The risk of memory deficit increased according to quintiles of tHcy both at baseline and at follow-up. A decline in tHcy, or an increase in folate, over a 6-year period was associated with a higher memory test score; and vice versa. These findings indicate that increased plasma tHcy is an independent risk factor for memory deficit both cross-sectionally and prospectively, and that a "favorable" change in folate or tHcy concentrations over time is associated with better memory performance.

Sustained weight loss in obese subjects has benefits that are independent of attained weight

OBJECTIVE

To explore the hypothesis that sustained weight loss in severely obese patients may have benefits that are independent of their attained BMI.

RESEARCH METHODS AND PROCEDURES

We conducted a comparison of two weight-stable groups with BMI in the 30 to 35 kg/m(2) range. Subjects (n = 79) were selected obese patients 3 years after laparoscopic adjustable gastric band surgery, and controls (n = 79) were obese patients seeking weight loss therapy. Subjects were selected in a de-identified manner from our database to best match the control group. A range of clinical, biochemical, and questionnaire measures were obtained to assess obesity-related health status

RESULTS

Subjects maintained a mean weight loss of 32.8 +/- 18 kg after surgery. The weight loss subjects had significantly lower fasting plasma glucose, insulin, and triglyceride concentrations, along with higher high-density lipoprotein-cholesterol levels and better indirect measures of insulin sensitivity when compared with controls (p < 0.05 for all). In addition, aminotransferase levels, neutrophil counts, and globulin levels were also significantly lower in weight loss subjects. All differences in laboratory variables remained significant after controlling for BMI. The subjects also reported better health-related quality of life, fewer symptoms of depression, and greater satisfaction with their appearance than controls.

DISCUSSION

These findings suggest that the post-weight loss state conveys benefits that are greater than predicted by the attained BMI. These findings may have important implications regarding the expectations of weight loss therapy, and mechanisms for this effect should be carefully sought.

Fish oil supplementation in pregnancy modifies neonatal progenitors at birth in infants at risk of atopy

Dietary n-3 polyunsaturated fatty acids (PUFA) may represent a mode of allergy prevention. Cord blood (CB) CD34+ hemopoietic progenitors are altered in infants at risk of atopy. We therefore studied the effects of dietary n-3 PUFA supplementation during pregnancy on numbers and function of progenitors in neonates at high risk of atopy. In a double-blind study, atopic, pregnant women were randomized to receive fish oil capsules or placebo from 20 wk gestation until delivery. At birth, CB CD34+ cells were isolated and analyzed by flow cytometry for expression of cytokine (IL-5Ralpha, IL-3Ralpha, granulocyte/macrophage colony-stimulating factor Ralpha) or chemokine (CXCR4 and CCR3) receptors. CB cells were also cultured in methylcellulose assays for eosinophil/basophil colony-forming cells. At age 1 y, infants were clinically assessed for atopic symptoms and skin tests. Percentages of CB CD34+ cell numbers were higher after n-3 PUFA than placebo. Co-expression of cytokine or chemokine receptors on CD34 cells was not altered by n-3 PUFA supplementation. However, there were significantly more IL-5-responsive CB eosinophil/basophil colony forming units (Eo/B-CFU) in the fish oil, compared with the control, group. Overall, there was a positive association between CD34+ cells and IL-5-responsive Eo/B-CFU in CB and 1 y clinical outcomes, including atopic dermatitis and wheeze. Dietary n-3 PUFA supplementation during pregnancy in atopic mothers alters infant cord blood hemopoietic progenitor phenotype. This may have an impact on development of atopic disease.

Comparison of isotope dilution mass spectrometry methods for the determination of total homocysteine in plasma and serum

Two independent methods have been critically evaluated and applied to the measurement of total homocysteine in serum and plasma: solid-phase anion extraction (SPAE) gas chromatography/mass spectrometry (GC/MS) and protein precipitation liquid chromatography/tandem mass spectrometry (LC/MS/MS). In addition, analysis of samples prepared by SPAE was accomplished by liquid chromatography/mass spectrometry (LC/MS) and LC/MS/MS. These methods have been used to determine total homocysteine levels in several existing serum-based Standard Reference Materials (SRMs) from the National Institute of Standards and Technology and in patient plasma samples provided by the Centers for Disease Control and Prevention. The precision of the homocysteine measurements in serum and plasma was critically evaluated, and method comparisons were carried out using Bland-Altman plots and bias analysis. On the basis of the excellent precision and close agreement of the mass spectrometric (MS) methods, the MS-based methods will be used for certification of a serum-based SRM for homocysteine and folates.

Associations between maternal methylenetetrahydrofolate reductase polymorphisms and adverse outcomes of pregnancy: the Hordaland Homocysteine Study

PURPOSE

Methylenetetrahydrofolate reductase (MTHFR) is involved in the metabolism of folate and homocysteine; a polymorphism in the MTHFR gene (677C-->T) has been associated with adverse outcomes of pregnancy. We studied whether two polymorphisms in the MTHFR gene (677C-->T and 1298A-->C) are associated with pregnancy complications, adverse outcomes, and birth defects.

METHODS

MTHFR polymorphisms were determined in blood collected in 1992 and 1993 from 5883 women aged 40 to 42 years, and linked with 14,492 pregnancies in the same women recorded in the Medical Birth Registry of Norway from 1967 to 1996.

RESULTS

The 677TT genotype in mothers was associated with increased risk of placental abruption (odds ratio [OR] = 2.6; 95% confidence interval [CI]: 1.4 to 4.8) compared with the CC variant. The risk of intrauterine growth restriction increased with number of T alleles (P for trend = 0.04). Compared with the 1298AA variant, the CC variant was associated with a reduced risk of very low birth weight infants (OR = 0.4; 95% CI: 0.2 to 0.8). No significant associations were found between MTHFR polymorphisms and birth defects.

CONCLUSION

The maternal MTHFR 677C-->T polymorphism was a risk factor for placental abruption. The unexpected protective effect of the 1298A-->C polymorphism on very low birth weight needs further study.

High-density lipoprotein and homocysteine levels correlate inversely in preeclamptic women in northern Nigeria

BACKGROUND

Preeclampsia/eclampsia is one of the most common complications of pregnancy. It is a cause of high morbidity for both mother and fetus, especially in developing countries. In a recent survey conducted in Gombe, Nigeria, eclampsia was found to be a major cause of maternal mortality (24.2%), second only to obstetric hemorrhage (27.1%). Previous studies have produced contradictory findings regarding total homocysteine (tHcy) levels in women with preeclampsia/eclampsia and there is little information about the relationship between particular serum lipids and tHcy. The objective of this study in Gombe was to compare the levels of serum lipids and homocysteine in healthy pregnant women and women with preeclampsia/eclampsia in Nigeria.

METHODS

The experimental subjects included 43 women with preeclampsia/eclampsia and 130 healthy pregnant women served as controls. The criteria for preeclampsia/eclampsia included the following: hypertension (blood pressure > 140/90 mmHg), total protein (> 190 mg/g creatinine), and edema. Blood sera obtained from patients and controls attending the prenatal clinics at the Specialist Hospital and the Federal Medical Center in Gombe were analyzed for tHcy, total cholesterol, triglycerides, high-density lipoprotein (HDL)-cholesterol, low-density lipoprotein (LDL)-cholesterol, antioxidant capacity, folate, and vitamin B-12.

RESULTS

The mean tHcy concentration for the preeclamptic/eclamptic women was greater than that of the controls (10.1 vs. 8.4 micromol/l, respectively, p = 0.01). The mean concentrations of LDL-cholesterol and triacylglycerols were not different between the two groups. However, the mean HDL-cholesterol level was higher in the healthy pregnant women compared with the preeclamptic/eclamptic women (1.64 vs. 1.42 mmol/l, respectively, p = 0.02). The HDL-cholesterol concentration was correlated inversely with the tHcy concentration (p = 0.001, r = 0.51). Total homocysteine was not linked with either serum folate or vitamin B-12.

CONCLUSIONS

These results show that preeclampsia/eclampsia is associated with increased tHcy levels and that HDL levels are depressed in Nigerian women with this hypertensive, pregnancy associated disorder.

Changes in lifestyle and plasma total homocysteine: the Hordaland Homocysteine Study

BACKGROUND

Elevated plasma concentrations of total homocysteine (tHcy) are a risk factor for cardiovascular disease. tHcy is a marker of folate and cobalamin deficiencies and is also related to several lifestyle factors.

OBJECTIVE

We examined whether changes in lifestyle influence tHcy over time.

DESIGN

A population-based, prospective study was conducted in 7031 subjects from western Norway who constituted 2 age groups (41-42 and 65-67 y) at baseline (1992-1993). The subjects were reinvestigated in 1997-1999 ( follow-up: 6 y).

RESULTS

During follow-up, median tHcy concentrations decreased 0.10 (25th and 75th percentiles: -1.24, 1.00) micromol/L in the younger subjects and increased 0.39 (25th and 75th percentiles: -0.99, 1.79) micromol/L in the older subjects. Changes in plasma vitamin status and vitamin supplement use were the strongest determinants of changes in tHcy over time. Each unit increase in plasma folate (nmol/L) and vitamin B-12 (pmol/L) was associated with reductions in tHcy concentrations of 0.2 and 0.1 micromol/L, respectively. Among the younger and older age groups, those who started to take vitamin supplements during follow-up had significant reductions in tHcy concentrations of 0.42 (95% CI: -0.65, -0.20) and 0.41 (-0.78, -0.03) micromol/L, respectively. In the younger subjects who quit smoking, tHcy concentrations decreased 0.54 (-0.91, -0.16) micromol/L. Weight changes were inversely related to tHcy. Both baseline history of cardiovascular disease or hypertension and cardiovascular events during follow-up were significantly associated with changes in tHcy.

CONCLUSIONS

Changes in lifestyle factors over time influence tHcy concentrations. These changes are modest when compared with the strong associations between tHcy and lifestyle factors in cross-sectional studies.

Hyperhomocysteinemia due to methionine synthase deficiency, cblG: structure of the MTR gene, genotype diversity, and recognition of a common mutation, P1173L

Mutations in the MTR gene, which encodes methionine synthase on human chromosome 1p43, result in the methylcobalamin deficiency G (cblG) disorder, which is characterized by homocystinuria, hyperhomocysteinemia, and hypomethioninemia. To investigate the molecular basis of the disorder, we have characterized the structure of the MTR gene, thereby identifying exon-intron boundaries. This enabled amplification of each of the 33 exons of the gene, from genomic DNA from a panel of 21 patients with cblG. Thirteen novel mutations were identified. These included five deletions (c.12-13delGC, c.381delA, c.2101delT, c.2669-2670delTG, and c.2796-2800delAAGTC) and two nonsense mutations (R585X and E1204X) that would result in synthesis of truncated proteins that lack portions critical for enzyme function. One mutation was identified that resulted in conversion of A to C of the invariant A of the 3' splice site of intron 9. Five missense mutations (A410P, S437Y, S450H, H595P, and I804T) were identified. The latter mutations, as well as the splice-site mutation, were not detected in a panel of 50 anonymous DNA samples, suggesting that these sequence changes are not polymorphisms present in the general population. In addition, a previously described missense mutation, P1173L, was detected in 16 patients in an expanded panel of 24 patients with cblG. Analysis of haplotypes constructed using sequence polymorphisms identified within the MTR gene demonstrated that this mutation, a C-->T transition in a CpG island, has occurred on at least two separate genetic backgrounds.