Hyperhomocysteinemia and vitamin B-12 deficiency in elderly using Title IIIc nutrition services

Homocysteine enhances bone resorption by stimulation of osteoclast formation and activity through increased intracellular ROS generation

Hyperhomocystinemia is a modifiable risk factor for osteoporosis and fracture. Physiologic concentrations of Hcy directly activate osteoclast formation and activity through stimulation of p38 MAPK and integrin beta3. The effects of Hcy were mediated by generation of intracellular ROS.

INTRODUCTION

Hyperhomocysteinemia is a modifiable risk factor for osteoporosis and its related bone fractures. It has been reported that bone resorption and turnover rate were increased in hyperhomocystinemia. Using mouse bone marrow cells, we examined the direct effects of homocysteine (Hcy) on osteoclast formation and activity.

MATERIALS AND METHODS

Osteoclast formation was determined by TRACP staining and TRACP activity. Intracellular reactive oxygen species (ROS) generation was measured using a fluorescent probe, dichlorodihydrofluorescein diacetate. Intracellular signaling cascades of p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and NF-kappaB were measured by Western blotting. Integrin beta3 mRNA levels were measured by RT-PCR. Actin ring formation and bone resorption assays were also performed.

RESULTS

Physiologic concentrations of Hcy upregulated TRACP+ multinucleated cells and TRACP activity, stimulated actin ring formation, and increased the number of nuclei per cell and the level of expression of integrin beta3 mRNA. In addition, Hcy increased bone resorption and stimulated p38 MAPK activity and intracellular reactive oxygen species (ROS) generation. All of these Hcy-induced changes were blocked by pretreatment with the antioxidant, N-acetyl cysteine.

CONCLUSIONS

Hcy directly activates osteoclast formation and activity through increased generation of intracellular ROS. These findings suggest that, in individuals with mild to moderate hyperhomocystinemia, increased bone resorption by osteoclasts may contribute to osteoporosis and that an antioxidant may attenuate bone loss in these individuals.

RETRACTED: Homocysteine as a predictive factor for hip fracture in elderly women with Parkinson's disease

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article is being retracted at the request of the Editor in Chief because of the stated concerns listed below. The article was accepted for publication by a previous editor and editorial board nearly 15 years ago, at a time when submissions and documentation were in paper form, prior to the transition of The American Journal of Medicine to a digital submission and review process. The records, including the original manuscript and peer reviewers' comments, are no longer extant and consequently we are unable to review the comments of the peer reviewers and the editors involved at that time. Nevertheless, the allegations of Grey et al. (as detailed in their Letter of Concern, published in the March 2018 issue of AJM, Volume 131, Issue 3, pages e107–e108; DOI: 10.1016/j.amjmed.2017.10.009) seem valid. A response by the Editor-in-Chief was also published in that issue. Therefore, given the documentation of Grey et al, the journal has concluded that this article should be considered as likely fraudulent and should not be quoted in the scientific literature in support of its conclusions. The article is severely compromised by wide-ranging and serious concerns about governance, ethics, authorship, implausible study conduct, implausible workload, discrepant participant numbers and treatment groups, impossible data, implausible data, implausible outcome data and discrepant methodology. The concerns are detailed in the afore-referenced letter of concern and can be summarized as follows: • It is stated that the study was approved by the Human Investigation Committee of the Futase Social Insurance Hospital, yet Futase Hospital did not have an ethics committee until 2010. • Given the size of the hospital and volume of clinics undertaken, it is highly unlikely that the stated number of participants could have been recruited within 3 months, or followed up as reported. • There are inconsistencies in the reported data. In Table 1 the mean ages of participants by quartiles of plasma homocysteine are 69.0, 70.6, 71.9, and 72.6 years. The corresponding mean years since menopause are 13.7, 14.6, 15.2, and 16.2 years, meaning that the average age of menopause is 55–57 years, implausibly older than the expected value of 50 years. The plasma homocysteine data in quartile 1 are incorrect. Among 50 women with a range of 6.1-9.0 μmol/L, the reported mean (standard deviation), 7.1 (2.5) μmol/L, is not possible. • In Table 3 the rate of hip fractures in the cohort (72 per 1000 patient-years) is implausibly high, being at least 3 to 4 times that reported in large observational studies of PD. The 51 incident hip fractures in 50 women in quartile 4 represents an astonishing hip fracture incidence of 227 per 1000 patient-years, yet only 6 women (3%) in this quartile were lost to follow-up (Table 1), and none was apparently treated with medications known to reduce fracture risk. The reported incident rates for hip fracture are incorrect. We have attempted to contact the authors regarding these concerns and have received no response. We are therefore retracting this article since the evidence presented indicates that there has been scientific misconduct. Joseph S. Alpert, MD Professor of Medicine, University of Arizona College of Medicine, Tucson, Arizona; Editor in Chief, The American Journal of Medicine

Elevated methylmalonic acid is related to cognitive impairement in older adults enrolled in an elderly nutrition program

Vitamin B12 status has been linked to cognitive impairment among older adults. Deficit in methylmalonic acid (MMA) may be reflective of cognitive impairment because it is a biochemically sensitive marker of B12 deficiency. In a cross-sectional study the contributions of different indices of B12 status, including serum B12, MMA and total homocysteine (tHcy), were measured in relation to cognitive functioning. B12 deficiency as measured by elevated MMA concentrations appeared to be most reflective of cognitive impairment and appeared to contribute unique variance to cognitive measures after controlling for other biochemical variables. Demographic variables, particularly education and age, were more strongly associated with cognitive measures than was MMA. Monitoring and reducing serum MMA concentrations by increasing the intake of vitamin B12 may provide protection against cognitive decline in this and other older populations.

Nutrition and health education intervention for whole grain foods in the Georgia older Americans nutrition programs

This study examined the effects of a nutrition education intervention on improving the intake and behaviors related to whole grain foods in congregate meal recipients in senior centers in north Georgia. Participants were a convenience sample and completed a pretest, an educational intervention, and a post-test (N = 84, mean age = 77 years, 88% female, 76% Caucasian, and 24% African American). At the pre-test, most participants agreed that eating more whole grain foods would help reduce their risk of cancer (69%), heart disease (76%), type 2 diabetes (65%), and bowel disorders (82%), but consumption of 11 whole grain foods was low (10.5 times/week). Following the intervention, participants were more likely to suggest one or more correct ways to identify whole grain foods (45 vs. 62%, P< or = 0.05), and to report an increased intake of whole grain bread, cereal, and crackers (5.8 vs. 6.9 times/week, P < or = 0.05). While awareness of the health benefits of whole grain foods was high, the intakes were low. As a first step, this intervention improved several aspects of the consumption of whole grain foods; however, additional interventions that target the individual and the congregate meal program are needed to increase intakes to the recommended three servings daily.

Effect of diet and red wine consumption on serum total antioxidant capacity (TAC), dehydroepiandrosterone-sulphate (DHEAS) and insulin-like growth factor-1 (IGF-1) in Italian centenarians

The traditional mediterranean diet is associated with a hope for longer survival. It has also been shown that the red wine possesses a protective effect against the oxidative stress. We studied TAC, the DHEAS and the IGF-1 in a group of 26 healthy centenarians, 17 women and 9 men, of the age range of 100--105 years. Furthermore, we analyzed also serum urate and bilirubin levels between drinkers and abstainers. Most of centenarian subjects have been moderate wine consumers (<500 ml/day of red wine). These subjects were subdivided as follows: (i) Group A: those who had maintained the style of their dietary habits as compared to the previous years (n=3 males, 10 females); (ii) Group B: those who actually consumed a diet being deficient compared to that of the previous years, but remained moderate drinkers of red wine (n=3 males, 4 females); and (iii) Group C: those who actually consumed a diet being deficient compared to that of the previous years, and at the same time, were abstainers in wine consumption (n=3 males, 3 females). The results show that in men three of the studied parameters decreased from Group A to C to considerable extents, as follows (mean+/-S.D.). TAC: 302.4+/-32.3; 142.0+/-24.1 and 96.4+/-20.1 micromol/l; DHEAS: 3.35+/-0.81; 2.52+/-0.18 and 1.34+/-0.14 micromol/l; IGF-1: 85.7+/-6.7; 76.6+/-6.7 and 65.6+/-2.6 ng/ml, respectively. For the same parameters, the results in the women were: TAC: 258.4+/-12.2; 182.1+/-14.0 and 107.6+/-10.0 micromol/l; DHEAS: 3.85+/-0.16; 2.34+/-0.19 and 2.05+/-0.04 micromol/l; IGF-1: 89.7+/-6.7; 76.6+/-4.7 and 64.2+/-2.7 ng/ml, respectively. We did not find any significant difference in the other serum parameters between drinkers (n=14) and abstainers (n=3) (urate: 267.6+/-52.9, and 289.5+/-80.1; bilirubin: 9.81+/-4.29 and 7.18+/-2.89 micromol/l, respectively). Our data suggest that the deteriorated diet caused a reduction of TAC, DHEAS and IGF-1 in the centenarians. However, red vine consumption exerted a protective effect against this trend, even if this protection is not reaching statistical significance in some cases (in men), which is due most probably to the lower number of male subjects in the study.

Cognitive performance in relation to vitamin status in healthy elderly German women-the effect of 6-month multivitamin supplementation

BACKGROUND

Prior investigations have reported a link between poor status of antioxidants, folate, and cobalamin resulting in elevated total plasma homocysteine (tHcy) and methylmalonic acid (MMA) concentrations with an increased risk for reduced cognitive performance. The aim of the study was to evaluate the effect of a 6-month multivitamin supplementation on the cognitive performance of female seniors and to assess cognitive functioning in relation to vitamin status, tHcy, and MMA values at baseline.

METHODS

The study was performed as a randomized placebo-controlled double-blind trial. 220 healthy, free-living women (aged 60-91 years) were included. Blood drawings and cognitive tests were performed at the Institute of Food Science of the University of Hanover, Germany. Vitamin and cognitive status have been evaluated prior to and 6 months after supplementation. Plasma ascorbic acid, serum concentrations of alpha-tocopherol, beta-carotene, and coenzyme Q10, serum and erythrocyte folate as well as serum cobalamin, serum MMA, and plasma tHcy concentrations were measured. Activity coefficient of erythrocyte alpha aspartic aminotransferase was used as functional index for vitamin B(6) status. The cognitive performance was assessed by the Symbol Search test, a subtest of the Wechsler Adult Intelligence Scale (WAIS-III) and the pattern-recognition test. Intelligence as assessed by the 'Kurztest für Allgemeine Intelligenz' (KAI) was a further variable.

RESULTS

No significant differences in pattern-recognition and intelligence score were observed between vitamin and placebo group prior to and after multivitamin supplementation. In the Symbol Search test, the vitamin group exhibited better test results than the placebo group at both measure points. One-way ANOVA showed a marginally significant linear trend between the baseline tHcy concentration and the pattern-recognition score (P = 0.051) in the total sample. Multiple backward regression revealed only a significant influence of the school graduation on baseline cognitive function test results. A general linear model showed that the changes in cognitive function scores could not be explained by the type of treatment or blood parameters.

CONCLUSIONS

Our data indicate that 6 months supplementation of physiological dosages of antioxidants and B vitamins have no effect on cognitive performance in presumedly healthy and well-nourished female seniors. An intervention period of only 6 months may be too short for improving cognitive performance in well-educated elderly women without dementia.

Homocysteine and vitamin B12 status relate to bone turnover markers, broadband ultrasound attenuation, and fractures in healthy elderly people

Hyperhomocysteinemia may contribute to the development of osteoporosis. The relationship of Hcy and vitamin B12 with bone turnover markers, BUA, and fracture incidence was studied in 1267 subjects of the Longitudinal Aging Study Amsterdam. High Hcy and low vitamin B12 concentrations were significantly associated with low BUA, high markers of bone turnover, and increased fracture risk.

INTRODUCTION

Hyperhomocysteinemia may contribute to the development of osteoporosis. Vitamin B12 is closely correlated to homocysteine (Hcy). The main objective of our study was to examine the association of Hcy and vitamin B12 status and the combined effect of these two with broadband ultrasound attenuation (BUA), bone turnover markers, and fracture.

MATERIALS AND METHODS

Subjects were 615 men and 652 women with a mean age of 76 +/- 6.6 (SD) years of the Longitudinal Aging Study Amsterdam (LASA). At baseline (1995/1996), blood samples were taken after an overnight fast for dairy products. Plasma Hcy was measured with IMx, serum vitamin B12 with competitive immunoassay (IA) luminescence, serum osteocalcin (OC) with immunoradiometric assay (IRMA), and urinary excretion of deoxypyridinoline (DPD) with competitive IA and corrected for creatinine (Cr) concentration. CVs were 4%, 5%, 8%, and 5%, respectively. BUA was assessed in the heel bone twice in both the right and left calcaneus. Mean BUA value was calculated from these four measurements. CV was 3.4%. After baseline measurements in 1995, a 3-year prospective follow-up of fractures was carried out until 1998/1999. Subjects were grouped by using two different approaches on the basis of their vitamin B12 concentration, normal versus low (<200 pM) or lowest quartile (Q1) versus normal quartiles (Q2-Q4), and Hcy concentration, normal versus high (>15 microM) or highest quartile (Q4) versus normal quartiles (Q1-Q3). Analysis of covariance was performed to calculate mean values of BUA, OC, and DPD/Cr(urine) based on the specified categories of Hcy and vitamin B12 and adjusted for several confounders (potential confounders were age, sex, body weight, body height, current smoking [yes/no], mobility, cognition). The relative risk (RR) of any fracture was assessed with Cox regression analysis. Quartiles were used when Hcy and vitamin B12 were separately studied in their relationship with fracture incidence.

RESULTS

Fourteen percent of the men and 9% of the women had high Hcy (>15 microM) and low vitamin B12 (<200 pM) concentrations. Women with vitamin B12 levels <200 pM and Hcy concentrations >15 microM had lower BUA, higher DPD/Cr, and higher OC concentrations than their counterparts. In men, no differences were found between the different Hcy and vitamin B12 categories in adjusted means of BUA, OC, or DPD/Cr(urine). Twenty-eight men and 43 women sustained a fracture during the 3-year follow-up period. The adjusted RR for fractures (95% CI) for men with high Hcy and/or low vitamin B12 concentrations was 3.8 (1.2-11.6) compared with men with normal Hcy and vitamin B12 concentrations. Women with high Hcy and/or low vitamin B12 concentrations had an adjusted RR for fractures of 2.8 (1.3-5.7).

CONCLUSIONS

High Hcy and low vitamin B12 concentrations were significantly associated with low BUA, high markers of bone turnover, and increased fracture risk.

Homocysteine and Osteoporotic Fracture Risk: A Potential Role for B Vitamins

Hyperhomocysteinemia (elevated plasma homocysteine levels) has been linked to increased risk of neural tube defects, cardiovascular disease, Alzheimer's dementia, pregnancy complications, and inflammatory bowel disease. Evidence for a role of hyperhomocysteinemia in the etiology of osteoporosis has recently been strengthened by the findings of two separate studies, which both reported that high homocysteine levels significantly increased risk of osteoporotic fracture. While the etiology of hyperhomocysteinemia is considered to be multifactorial (including genetic, nutritional, and lifestyle factors), a deficiency of one or more B vitamins certainly has a role. These vitamins are involved in the metabolism and clearance of homocysteine, and thus may have a protective effect against osteoporotic fracture risk.

Cobalamin: a critical vitamin in the elderly

Vitamin B(12) deficiency is a common problem in elderly subjects. If a serum cobalamin level of about 150 pmol/L (200 pg/mL) is considered normal, 10-15% of the elderly are deficient. Today, however, a threshold of 220-258 pmol/L (300-350 pg/mL) is recognized as desirable in the elderly, or else sensitive markers like the blood concentration of homocysteine or methylmalonic acid (MMA) are used. Then the prevalence of cobalamin deficiency rises to up to 43%. In the elderly, this high prevalence of poor cobalamin status is predominantly caused by atrophic gastritis type B. Atrophic gastritis results in declining gastric acid and pepsinogen secretion, and hence decreasing intestinal absorption of the cobalamin protein complexes from food. About 20-50% of the elderly are affected. Furthermore, the reduced acid secretion leads to an alkalinization of the small intestine, which may result in bacterial overgrowth and thus to a further decrease of the bioavailability of the vitamin. In addition, some drugs such as proton pump inhibitors or H2 receptor antagonists inhibit the intestinal absorption of vitamin B(12). An already moderately reduced vitamin B(12) level is associated with vascular disease and neurocognitive disorders such as depression and impaired cognitive performance. Furthermore, a poor vitamin B(12) status is assumed to be involved in the development and progression of dementia (e.g., Alzheimer's dementia). This is especially observable if the folic acid status is reduced as well. Due to the insecure supply, the cobalamin status of elderly persons (>/=60 years) should be regularly controlled and a general supplementation with vitamin B(12) (>50 microg/day) should be considered.

Cobalamin-responsive disorders in the ambulatory care setting: unreliability of cobalamin, methylmalonic acid, and homocysteine testing

Early recognition of cobalamin (Cbl)-responsive disorders in the ambulatory care setting is essential to prevent irreversible neurologic deficits. However, diagnostic algorithms using Cbl, methylmalonic acid (MMA), and homocysteine (HCys) measurements reflect studies in academic centers, and their negative predictive values have not been established. Thus, records of 456 ambulatory patients evaluated for Cbl deficiency at a staff model HMO were reviewed. Pretherapy Cbl, MMA, and HCys values in individual patients varied by 23%, 23%, and 17%, respectively, over 2 to 6 weeks. Hematologic or neurologic responses to pharmacologic doses of Cbl occurred in 37 of the 95 evaluable patients. In these patients, pretherapy Cbl, MMA, and HCys values were normal in 54%, 23%, and 50%, respectively. If therapy had been restricted to symptomatic patients with both low or intermediate Cbl levels and increased metabolite values, 63% of responders would not have been treated. Twenty-five patients did not respond to treatment, including 5 of 11 patients (45%) with low Cbl, 22 of 49 patients (45%) with high MMA, and 13 of 30 patients (43%) with high HCys values. It is concluded that Cbl, MMA, and HCys levels fluctuate with time and neither predict nor preclude the presence of Cbl-responsive hematologic or neurologic disorders.

Vitamin B12 deficiency as a worldwide problem

Pernicious anemia is a common cause of megaloblastic anemia throughout the world and especially in persons of European or African descent. Dietary deficiency of vitamin B12 due to vegetarianism is increasing and causes hyperhomocysteinemia. The breast-fed infant of a vitamin B12-deficient mother is at risk for severe developmental abnormalities, growth failure, and anemia. Elevated methylmalonic acid and/or total homocysteine are sensitive indicators of vitamin B12-deficient diets and correlate with clinical abnormalities. Dietary vitamin B12 deficiency is a severe problem in the Indian subcontinent, Mexico, Central and South America, and selected areas in Africa. Dietary vitamin B12 deficiency is not prevalent in Asia, except in vegetarians. Areas for research include intermittent vitamin B12 supplement dosing and better measurements of the bioavailability of B12 in fermented vegetarian foods and algae.

Homocysteine as a predictive factor for hip fracture in older persons

BACKGROUND

The increased prevalence of osteoporosis among people with homocystinuria suggests that a high serum homocysteine concentration may weaken bone by interfering with collagen cross-linking, thereby increasing the risk of osteoporotic fracture. We examined the association between the total homocysteine concentration and the risk of hip fracture in men and women enrolled in the Framingham Study.

METHODS

We studied 825 men and 1174 women, ranging in age from 59 to 91 years, from whom blood samples had been obtained between 1979 and 1982 to measure plasma total homocysteine. The participants in our study were followed from the time that the sample was obtained through June 1998 for incident hip fracture. Sex-specific, age-adjusted incidence rates of hip fracture were calculated for quartiles of total homocysteine concentrations. Cox proportional-hazards regression was used to calculate hazard ratios for quartiles of homocysteine values.

RESULTS

The mean (+/-SD) plasma total homocysteine concentration was 13.4+/-9.1 micromol per liter in men and 12.1+/-5.3 micromol per liter in women. The median duration of follow-up was 12.3 years for men and 15.0 years for women. There were 41 hip fractures among men and 146 among women. The age-adjusted incidence rates per 1000 person-years for hip fracture, from the lowest to the highest quartile for total homocysteine, were 1.96 (95 percent confidence interval, 0.52 to 3.41), 3.24 (0.97 to 5.52), 4.43 (1.80 to 7.07), and 8.14 (4.20 to 12.08) for men and 9.42 (5.72 to 13.12), 7.01 (4.29 to 9.72), 9.58 (6.42 to 12.74), and 16.57 (11.84 to 21.30) for women. Men and women in the highest quartile had a greater risk of hip fracture than those in the lowest quartile--the risk was almost four times as high for men and 1.9 times as high for women.

CONCLUSIONS

These findings suggest that the homocysteine concentration, which is easily modifiable by means of dietary intervention, is an important risk factor for hip fracture in older persons.

Homocysteine and reactive oxygen species in metabolic syndrome, type 2 diabetes mellitus, and atheroscleropathy: the pleiotropic effects of folate supplementation

Homocysteine has emerged as a novel independent marker of risk for the development of cardiovascular disease over the past three decades. Additionally, there is a graded mortality risk associated with an elevated fasting plasma total homocysteine (tHcy). Metabolic syndrome (MS) and type 2 diabetes mellitus (T2DM) are now considered to be a strong coronary heart disease (CHD) risk enhancer and a CHD risk equivalent respectively. Hyperhomocysteinemia (HHcy) in patients with MS and T2DM would be expected to share a similar prevalence to the general population of five to seven percent and of even greater importance is: Declining glomerular filtration and overt diabetic nephropathy is a major determinant of tHcy elevation in MS and T2DM.

There are multiple metabolic toxicities resulting in an excess of reactive oxygen species associated with MS, T2DM, and the accelerated atherosclerosis (atheroscleropathy). HHcy is associated with an increased risk of cardiovascular disease, and its individual role and how it interacts with the other multiple toxicities are presented.

The water-soluble B vitamins (especially folate and cobalamin-vitamin B₁₂) have been shown to lower HHcy. The absence of the cystathionine beta synthase enzyme in human vascular cells contributes to the importance of a dual role of folic acid in lowering tHcy through remethylation, as well as, its action of being an electron and hydrogen donor to the essential cofactor tetrahydrobiopterin. This folate shuttle facilitates the important recoupling of the uncoupled endothelial nitric oxide synthase enzyme reaction and may restore the synthesis of the omnipotent endothelial nitric oxide to the vasculature.

Prevalence and outcomes of anemia in geriatrics: a systematic review of the literature

Anemia is a common concern in geriatric health, but its exact incidence and prevalence are unclear. Several studies have addressed this issue with discrepant results. Estimates of anemia prevalence reported in the articles reviewed here range from 2.9% to 61% in elderly men and from 3.3% to 41% in elderly women. This variability is related to a number of factors, including the setting of the study, the health status of the subject population, and the criteria used to define anemia. The criteria set by the World Health Organization (WHO)--hemoglobin level <120.0 g/L for women and <130.0 g/L for men--are most frequently, but not universally, used. Even so, their appropriateness in older populations may be questioned. Most existing reports indicate that elderly men have higher rates of anemia than do elderly women, but the threshold values are, in general, higher for men than for women. Incidence of anemia rises with age; some studies report a particularly notable increase in prevalence of anemia in the oldest subjects, those > or =85 years of age. Whereas anemia is associated with symptoms ranging from weakness and fatigue to increased falls and depression, and in severe cases can lead to congestive heart failure, few studies have systematically examined functional, clinical, and economic outcomes or patient satisfaction in the elderly with anemia. Future directions for research on anemia should include a more detailed examination of the importance of aging or age-related diseases on the pathogenesis of anemia, an assessment of the importance of anemia on outcomes such as physical function and cognitive function, and an analysis of whether impairments associated with anemia are amenable to correction by improving hemoglobin concentration.

Facts and Recommendations about Total Homocysteine Determinations: An Expert Opinion

Background: Measurement of plasma total homocysteine has become common as new methods have been introduced. A wide range of disorders are associated with increased concentrations of total homocysteine. The purpose of this review is to provide an international expert opinion on the practical aspects of total homocysteine determinations in clinical practice and in the research setting and on the relevance of total homocysteine measurements as diagnostic or screening tests in several target populations.

Methods: Published data available on Medline were used as the basis for the recommendations. Drafts of the recommendations were critically discussed at meetings over a period of 3 years.

Outcome: This review is divided into two sections: (a) determination of homocysteine (methods and their performance, sample collection and handling, biological determinants, reference intervals, within-person variability, and methionine loading test); and (b) risk assessment and disease diagnosis (homocystinuria, folate and cobalamin deficiencies, cardiovascular disease, renal failure, psychiatric disorders and cognitive impairment, pregnancy complications and birth defects, and screening of elderly and newborns). Each of these subsections concludes with a separate series of recommendations to assist the clinician and the research scientist in making informed decisions. The review concludes with a list of unresolved questions.

Update on Cobalamin, Folate, and Homocysteine

Three topics affecting cobalamin, folate, and homocysteine that have generated interest, activity, and advances in recent years are discussed. These are: (I) the application of an expanded variety of tools to the diagnosis of cobalamin deficiency, and how these affect and are affected by our current understanding of deficiency; (II) the nature of the interaction between homocysteine and vascular disease, and how the relationship is affected by vitamins; and (III) the improved understanding of relevant genetic disorders and common genetic polymorphisms, and how these interact with environmental influences.

The diagnostic approach to cobalamin deficiency now allows better diagnosis of difficult and atypical cases and more confident rejection of the diagnosis when deficiency does not exist. However, the process has also become a complex and sometimes vexing undertaking. Part of the difficulty derives from the lack of a diagnostic gold standard among the many available tests, part from the overwhelming numerical preponderance of patients with subclinical deficiency (in which isolated biochemical findings exist without clinical signs or symptoms) among the cobalamin deficiency states, and part from the decreased availability of reliable tests to identify the causes of a patient’s cobalamin deficiency and thus a growing deemphasis of that important part of the diagnostic process. In Section I, Dr. Carmel discusses the tests, the diagnostic issues, and possible approaches to the clinical evaluation. It is suggested no single algorithm fits all cases, some of which require more biochemical proof than others, and that differentiating between subclinical and clinical deficiency, despite their overlap, may be a helpful and practical point of departure in the evaluation of patients encountered in clinical practice. The arguments for and against a suggested expansion of the cobalamin reference range are also weighed.

The epidemiologic data suggest that homocysteine elevation is a risk factor for vascular and thrombotic disease. In Section II, Dr. Green notes that the interactions of metabolism and clinical risk are not well understood and a causative relationship remains unproven despite new reports that lowering homocysteine levels may reduce vascular complications. Genetic and acquired influences may interact in important ways that are still being sorted out. The use of vitamins, especially folate, often reduces homocysteine levels but also carries potential disadvantages and even risks. Folate fortification of the diet and supplement use have also markedly reduced the frequency of folate deficiency, and cobalamin deficiency is now the more common deficiency state, especially among the elderly.

Although genetic disorders are rare, they illuminate important metabolic mechanisms and pose diagnostic challenges, especially when clinical presentation occurs later in life. In Section III, Drs. Rosenblatt and Watkins use selected disorders to illustrate the subject. Imerslund-Gräsbeck syndrome, a hereditary disorder of cobalamin absorption at the ileal level, demonstrates genetic heterogeneity. Finnish patients show mutation of the gene for cubilin, the multiligand receptor for intrinsic factor. Surprisingly, Norwegian and other patients have been found recently to have mutations of the AMN (amnionless) gene, mutations that are lethal in mice at the embryonic stage. Two disorders of cobalamin metabolism, cblG and cblE, are now known to arise from mutations of the methionine synthase and methionine synthase reductase genes, respectively. These disorders feature megaloblastic anemia and neurologic manifestations. The folate disorder selected for illustration, methylenetetrahydrofolate reductase (MTHFR) deficiency, paradoxically causes neurological problems but no megaloblastic anemia. This rare deficiency is the most common inborn error of folate metabolism. It is distinct from the very common MTHFR gene polymorphisms, mutations that cause mild to moderate reductions in MTHFR activity but no direct clinical manifestations. The MTHFR polymorphisms, especially the 677C→T mutation, may contribute to vascular and birth defect risks, while reducing the risk of certain malignancies, such as colon cancer. These polymorphisms and those of genes for other enzymes and proteins related to cobalamin, folate, and homocysteine metabolism may be important role players in frequent interactions between genes and the environment.