Associations of blood homocysteine concentrations in Arab schizophrenic patients

Clinical Biochemistry 40 (2007) 1026 – 1031

Associations of blood homocysteine concentrations in Arab schizophrenic patients A.O. Akanji a,⁎, J.U. Ohaeri b , S.A. Al-Shammri c , H.R. Fatania d a

Clinical Chemistry Unit, Department of Pathology, Faculty of Medicine, Kuwait University, P O Box 24923 Safat, 13110 Kuwait b Department of Psychiatry, Psychological Medicine Hospital, Kuwait c Department of Medicine, Kuwait University Faculty of Medicine, Kuwait d Department of Biochemistry, Kuwait University Faculty of Medicine, Kuwait Received 7 April 2007; received in revised form 20 May 2007; accepted 1 June 2007 Available online 8 June 2007

Abstract Background: This study aimed to evaluate the blood homocysteine concentration in Arab patients with schizophrenia and assess its associations with clinical phenotypes of the disease. Subjects and methods: Two age-matched groups of subjects were studied: (1) Healthy Controls, HC, n = 165; (2) patients with schizophrenia, SZ: n = 207. Each subject was evaluated with a standard questionnaire for age at disease onset, family history, disease severity and outcome. Plasma homocysteine levels (Hcys) were measured by immunoassay and serum levels of other biochemical parameters were measured by routine Autoanalyzer techniques. Results and discussion: Group HC was heavier (body mass index, BMI) while SZ had greater waist–hip ratio (WHR) and plasma Hcys levels. In SZ, there were significant correlations between Hcys and BMI, triglycerides and HDL. Hcys levels in SZ were highest in the younger male patients. Conclusion: Schizophrenic patients have increased blood Hcys levels which correlate with components of the metabolic syndrome. Hcys levels were highest in the younger male patients and were not influenced by prognostic features of the disease. © 2007 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved. Keywords: Arabs; Schizophrenia; Homocysteine; Lipoproteins; Oxidative stress; Disease phenotypes

Introduction Schizophrenia is a complex genetic disorder most likely involving multiple genes of small effect. It is an important cause of psychiatric morbidity and handicap worldwide, including in the Arabian Gulf Region [1–3]. The pathogenesis of schizophrenia is essentially unknown but associations with such phenomena as heredity, autoimmunity and neural inflammation have been described [4–6]. Homocysteine is a sulphur containing amino acid, derived from methionine and normally converted to cysteine and partly remethylated to methionine via enzymatic processes involving

⁎ Corresponding author. Fax: + 965 533 8905. E-mail address: [email protected] (A.O. Akanji).

vitamin B12 and folate as cofactors. Recently, homocysteine has been widely investigated for its putative role in the genesis of a variety of cardiovascular and neuropsychiatric disorders [7– 12]. The harmful effects of homocystinemia are believed due to generation of oxidants (reactive oxygen species) during its further catabolism, which could oxidize membrane lipids and proteins, including enzymes [13]. Indeed, more recently, it has been suggested that homocysteine may be important in the development and clinical expression of schizophrenia [14–17]. In investigating this hypothesis further, we embarked on this prospective case-control study, to compare plasma homocysteine levels in a schizophrenic Kuwaiti Arab population with levels in age-matched healthy control subjects. We also aimed to evaluate the relationships, if any, of homocysteine levels, with some aspects of the clinical phenotype of the disease.

0009-9120/$ - see front matter © 2007 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.clinbiochem.2007.06.001

A.O. Akanji et al. / Clinical Biochemistry 40 (2007) 1026–1031

Subjects and methods Subjects We admitted two age-matched groups of subjects into the study after informed voluntary consent: 1. Healthy Controls, HC: n = 165 apparently healthy control subjects, median age (range) 38.0 (22.0–61.0 years), recruited from the Central Blood Bank, Kuwait, with subjects presenting for regular blood donation from the whole city state. Each subject was evaluated to exclude history of epilepsy, substance abuse, organic brain syndromes, diabetes, hypertension, chronic infections, coronary heart disease and self/family history of any mental illness including severe depression, mania and/or psychotic illness and/or medications for these. 2. Patients with schizophrenia, SZ: n = 207 patients, median age (range) 36.0 (15.0–76.0 years), with proven chronic schizophrenia diagnosed according to the DSM-IV criteria [18–20] and considered relatively stable on antipsychotic medication. They had been diagnosed as schizophrenics and on followup for at least one year after initial presentation at the Psychiatric Hospital, Kuwait. None had any associated co-morbidity (especially epilepsy, substance abuse, organic brain syndrome, chronic infections and coronary heart disease). Written informed consent was obtained from the patients in all cases in the presence of nurses. Psychiatric assessment was done with the following instruments: - The schizophrenia section of the WHO Schedule for Clinical Assessment in Neuropsychiatry (SCAN); - The Positive and Negative Syndrome Scale (PANSS) [21]; - Andreasen's Scale for Assessment of Negative Symptoms (SANS) [22]; - The Clinical Global Impression Scale ( severity) (CGI); - The Simpson and Angus Scale for extrapyramidal reactions; - The Barnes Akathisia Scale; - The Abnormal Involuntary Movement Scale (AIMS) for Tardive Dyskinesia (TD); and - The Family History General Screening Questionnaire (FIGS). Each recruited SZ patient was assessed according to a detailed questionnaire administered by an experienced psychiatrist, to the patient with his/her relatives, with particular attention to the following: 1. age, mode and date of onset of symptoms, including how patient was brought to hospital and when a definitive diagnosis was made; 2. family history of mental illness including psychosis, depression, anxiety disorders, epilepsy and drug abuse; 3. psychosocial outcome: including the outcome of marriage, education and employment over the years;

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4. number and duration of admissions over the years; 5. clinical global impression scale: severity, as assessed after at least 1 year of follow-up: 1 = normal, not all ill (clinically in remission); 2–4 = mild-to-moderately ill; 5–7 = severe: markedly or severely ill or among the most extremely ill]; and 6. pattern of clinical outcome over the years, classified as: good outcome (episodic remittent with fairly normal psychosocial functioning in-between episodes) or poor outcome (frequent relapses and/or chronically ill with residual symptoms and poor functioning socially and occupationally). It was not always possible to obtain complete demographic and clinical parameters in all the patients because of the nature of their illness. Social classification in Kuwait is essentially homogeneous with a cradle-to-grave welfare system, so both groups HC and SZ belonged essentially to a similar socioeconomic class. We obtained ethical approval for the study from both the Kuwait University and Psychiatric Hospital Institutional Research Ethics Committees. Methods Each subject (patient and control) was also assessed clinically with the exclusion criteria indicated above. Anthropometric measurements of height, weight and waist and hip circumferences were taken and the body mass index (BMI) and waist–hip ratio (WHR) were calculated. Each subject also gave a fasting blood sample, from which plasma (or serum) was extracted for glucose and routine biochemical indices of liver and kidney function and lipids (total cholesterol (TC), triglycerides (TG), high density lipoprotein cholesterol (HDL-C) analyses of which were done on a Beckman-Coulter LX-20 Autoanalyzer (Beckman-Coulter Inc., Fullerton, CA, USA)). Low density lipoprotein cholesterol (LDL-C) levels were derived from the Friedewald et al.'s [23] formula in all cases with total serum TG b4.5 mmol/L. Serum levels of Apo B were determined by nephelometry on a Beckman IMMAGE Analyzer (BeckmanCoulter Inc., Fullerton, CA, USA). Plasma total homocysteine (Hcys) levels were determined by a solid phase chemiluminescent immunometric assay using dedicated kits (IMMULITE 1000 Analyzer, DPC, CA, USA); the analytical sensitivity of the method was 0.5 μmol/L with intraand inter-run precision of 6.0–9.5% at concentrations from 2.0 to 50.0 μmol/L. Serum folate levels were measured by a competitive, liquidphase, ligand-labeled protein-binding chemiluminescent assay with in situ immobilization, using dedicated kits (IMMULITE 1000 Analyzer, DPC, CA, USA); the analytical sensitivity of the method was 0.3 ng/mL with intra- and inter-run precision of 4.0–9.0% at concentrations from 0.5 to 25.0 ng/mL. Serum vitamin B12 levels were determined by a solid phase competitive chemiluminescent immunometric assay using dedicated kits (IMMULITE 1000 Analyzer, DPC, CA, USA) with a preliminary heat denaturation step; the analytical sensitivity of the method was 50 pg/mL with intra- and inter-run precision of 5.0–12.5% at concentrations from 100 to 1200 pg/mL.

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Batch analyses for these analytes were done on serum samples stored frozen at − 20 °C without thawing within 4 weeks of sample collection. Data analysis The results are expressed as medians (ranges) as appropriate, and the differences between the two groups (HC and SZ) in relation to anthropometric and demographic indices and routine biochemical and lipid parameters were assessed by Mann–Whitney U tests. Differences in categorical variables within SZ, in relation to the clinical phenotype of disease (gender, age of onset, family history of psychosis, clinical severity, outcome, as defined in the Subjects section), were assessed by χ2, Fisher's Exact and Kruskal–Wallis tests as appropriate. The correlations between tHcys levels and the anthropometric, demographic and biochemical parameters were explored using Spearman's rank correlation coefficients and forward stepwise logistic regression analyses. These tests were performed by computer using the SPSS software. A p value b 0.05 was considered significant. Results The study included 207 patients with schizophrenia (Group SZ) and 165 healthy control subjects (Group HC). Table 1 shows that the two groups of subjects were similar in age, but while HC tended to be heavier (BMI, p = 0.01), those with SZ had greater WHR (p b 0.01). Additionally, the fasting serum concentrations of total cholesterol (p b 0.01), triglycerides (p b 0.01), LDL-cholesterol (p b 0.01), urate (p b 0.01) and apo B (p b 0.01) were greater in the healthy control subjects although HDL-cholesterol levels did not differ significantly between the two groups. Plasma total homocysteine (Hcys) levels were higher in the schizophreTable 1 Demographic, anthropometric and biochemical parameters in the groups of schizophrenic patients and healthy control subjects (results expressed as medians (range)) Variables

SZ

HC

p⁎

No. of Subjects Age (years) BMI (kg/m2) WHR Glucose (mmol/L) TC (mmol/L) TG (mmol/L) HDL (mmol/L) LDL (mmol/L) Uric acid (μmol/L) Apo B (g/L) tHcys (μmol/L) Vitamin B12 (pg/mL) Folate (ng/mL)

207 36 (15–76) 26.4 (14.0–53.2) 0.97 (0.76–1.18) 4.9 (0.1–18.6) 4.3 (2.5–8.8) 1.36 (0.29–10.17) 0.83 (0.17–2.03) 2.51 (0.19–5.51) 273 (61–455) 0.84 (0.41–1.86) 9.9 (2.2–42.0) 225 (120–735) 8.6 (3.2–12.9)

165 38 (22–61) 29.0 (19.8–45.7) 0.94 (0.81–1.11) 5.7 (4.0–20.1) 4.7 (2.4–8.4) 1.73 (0.39–8.71) 0.82 (0.42–2.02 ) 2.98 (0.92–5.24) 329 (165–579) 0.96 (0.43–1.70) 5.7 (2.3–19.3) 233 (103–706) 7.6 (2.6–13.5)

0.71 0.01 0.01 b0.01 b0.01 b0.01 0.24 b0.01 b0.01 b0.01 b0.01 0.26 0.22

Abbreviations: SZ, schizophrenic patients; HC, healthy control subjects; BMI, body mass index; WHR, waist/hip ratio; TC, total cholesterol; TG, triglycerides; apo B, apolipoprotein B; tHcys, total homocysteine. p⁎: for differences between schizophrenic patients and healthy control subjects (Mann–Whitney U tests).

Table 2 Spearman's rank correlation coefficients of plasma homocysteine with anthropometric and biochemical parameters in schizophrenic patients (SZ) and healthy control (HC) subjects tHcys

SZ

Variables

rs

p

HC rs

p

Age (years) BMI (kg/m2) WHR Glucose (mmol/L) TC (mmol/L) TG (mmol/L) HDL (mmol/L) LDL (mmol/L) Uric acid (μmol/L) ApoB (g/L)

0.04 0.20 0.01 −0.10 −0.09 0.18 −0.20 −0.12 −0.08 −0.08

0.52 0.05 0.95 0.08 0.11 0.02 0.01 0.10 0.17 0.17

0.17 0.02 0.08 −0.06 0.10 0.04 0.07 0.06 0.07 0.08

0.08 0.84 0.51 0.53 0.32 0.67 0.51 0.52 0.50 0.40

For abbreviations, please see Table 1.

nic patients (p b 0.01) but serum folate and vitamin B12 concentrations did not differ significantly between the two groups. A forward stepwise logistic regression model was used to determine the presence of an independent association between Hcys levels and subject group (SZ vs. HC) after adjustment for age and sex. This model suggested that, while age was not a significant confounding factor, gender was (β coefficient 2.44, p = 0.032). However, after adjustment for the effect of gender, Hcys levels remained significantly greater in the SZ group (β coefficient 0.37, p b 0.001, OR 1.45 (95% CI 1.26–1.67). Serum urea and creatinine levels were also similar for the SZ and HC groups– renal function, as assessed by these parameters, was normal in all the subjects. Table 2 shows the linear correlations established between plasma Hcys levels and the various anthropometric, demographic and biochemical parameters assessed in both groups of patients. It would appear that the determinants of Hcys differed slightly between the SZ and HC groups, for while, in the former, there were significant correlations of Hcys with BMI (rs = 0.20, p = 0.05), TG (rs = 0.18, p = 0.02) and negatively with HDL (rs = − 0.20, p = 0.01), we could not establish any significant associations of Hcys with any of the parameters assessed in the latter. In Table 3, we attempted to relate Hcys concentrations with some aspects of the clinical phenotype of schizophrenia in the patients in whom full clinical, demographic, anthropometric and biochemical information was available, especially in relation to the specific variables under consideration. The results suggest that the Hcys levels: 1. were significantly higher in men as compared to women (p = 0.01), and while levels were age-related in men, being higher in the younger (age b 40 years) in comparison to the older (age N 40 years) men, no such distinction could be made in the women; 2. were not influenced by age of onset of the disease in both men and women, with the age of onset categorized as b 20 years, 21–30 years and N 30 years;

A.O. Akanji et al. / Clinical Biochemistry 40 (2007) 1026–1031 Table 3 Plasma homocysteine levels in relation to clinical expression in Arab schizophrenic patients (results are expressed as median (range)). Variable Gender Male (n = 140) Female (n = 55) Age grouping (males) Age b40 years (n = 54) Age ≥40 years (n = 41) Age of onset (all patients) b20 years (n = 47) 21–30 years (n = 48) N30 years (n = 31) Age of onset (male patients) b20 years (n = 35) 21–30 years (n = 35) N30 years (n = 24) Age of onset (female patients) b20 years (n = 12) 21–30 years (n = 13) N30 years (n = 7) Disease severity Normal—in remission (n = 4) Mild-to-moderate (n = 59) Severe (n = 38) Family history of psychosis Positive (n = 43) Negative (n = 70) Disease outcome Good (n = 28) Poor (n = 74) Symptomatology Negative (n = 58) Non-negative (n = 36) Catatonia Present (n = 13) Absent (n = 81)

Hcys (μmol/L)

p⁎

10.4 (2.9–42.0) 8.4 (2.2–30.7)

0.01

11.3 (4.4–42.0) 9.0 (3.5–21.6)

0.04

9.7 (2.2–41.5) 9.6 (3.3–42.0) 9.8 (3.5–21.6)

0.98

10.4 (4.4–41.5) 11.2 (4.5–42.0) 9.6 (3.5–21.6)

0.47

8.2 (2.2–20.3) 5.9 (3.3–17.2) 10.5 (4.0–13.8)

0.33

8.1 (6.9–14.4) 10.4 (3.5–42.0) 11.0 (2.2–21.8)

0.98

11.6 (3.3–42.0) 9.4 (2.2–25.3)

0.08

8.8 (3.5–25.3) 10.6 (2.2–25.3)

0.31

10.5 (4.0–41.5) 11.0 (3.9–42.0)

0.92

11.4 (6.4–15.1) 10.5 (3.9–25.3)

0.95

Hcys: plasma total homocysteine level; n: number of subjects in each sub-group for which particular information is available. p⁎: for differences between values of components of sub-groups under each variable.

3. were not influenced by disease severity when the SZ patients were clinically categorized as being ‘normal’ (in remission) or having mild-to-moderate disease or severe illness; 4. showed a trend (approaching statistical significance) towards higher levels (p 0.08) in those patients with a family history of psychosis in comparison to those without; and 5. were not significantly influenced by disease outcome (good vs. poor), presence or absence of catatonia and association with negative or non-negative symptomatology 6. were not significantly related to urea, creatinine, folate and vitamin B12 levels (data not shown on Table 3). Discussion Elevated plasma homocysteine (Hcys) has recently been found to be a risk factor for a variety of central nervous system (CNS) disease processes including Alzheimer disease [10–12] and schizophrenia. With respect to schizophrenia (SZ), plasma

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hyper-homocystinaemia has been suggested as a risk factor, although published reports to that effect have not always been consistent [14–17,24]. In this study, we have evaluated blood levels of Hcys in SZ patients and an age-matched group of healthy control (HC) subjects. The results are in general agreement with the consensus view that homocysteine levels are increased in patients with SZ [14–17]. Moreover, in this study, blood Hcys levels were higher in males than in females and in the former were even higher in the younger age groups. These observations, probably the first from an Arabian Gulf population, are in keeping with previous reports in other populations, mainly Western and Caucasian, that the relationship of tHcys with schizophrenia may be influenced by age and gender [25–27]. It had also been suggested that Hcys could influence the clinical expression in SZ [16,28] with higher levels being associated with clinical deterioration. The results from this study do not however agree with that contention since we could not demonstrate that Hcys levels were influenced by age of onset of disease, severity of disease and outcome (as assessed from global clinical outcome scales) and specific symptomatology— negative vs. non-negative and presence or absence of catatonia. It is unlikely that the elevated Hcys levels, we (in this study) and others have observed in SZ patients, are due to treatment since it has been reported previously that increased Hcys levels are seen in both newly admitted (drug naïve) and chronic cases [16,17,25,29]. The differences are also unlikely to be due to renal dysfunction in the SZ group, as we established that serum urea and creatinine levels were within our hospital reference range for all in the study population (HC + SZ) and essentially similar for both groups. The other potential confounding factor may be the vitamin nutriture, especially as it has been speculated that Hcys may just be a marker for the poor nutrition generally seen in schizophrenic patients. It is known that Hcys levels rise consistently in states of folate and vitamin B12 deficiency, since both of these vitamins are cofactors for enzymes involved in the remethylation of Hcys to methionine [13,30,31]. Indeed, several nutritional (especially low dietary intake of folate and B12) and nonnutritional (including smoking, sedentary life style, poor renal function, low maternal folate and homocysteine level) factors have been invoked to explain the elevated homocysteine level in schizophrenia [30,32,33]. However, a multiple linear regression analysis of the determinants of plasma Hcys levels in SZ patients with a model inclusive of gender and plasma folate and B12 levels reported that less than 25% of the variance in male patients was explained by the model [34] and another study [29] affirmed that poor hospital nutrition was not responsible for the hyper-homocysteinaemia observed in newly admitted SZ patients. In this study, as well, we do not believe that our results are due to malnutrition in the SZ patients. Body weight as assessed by BMI and WHR differed only slightly between the HC and SZ groups; indeed, BMI was only slightly higher in HC while WHR was slightly higher in SZ. Moreover, although tHcys levels correlated weakly with BMI, there was no significant

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relationship with WHR in the SZ group. Furthermore, serum folate and vitamin B12 levels did not differ significantly between the two groups (HC vs. SZ, Table 1) or the various SZ sub-groups analyzed in Table 3. One observation of some interest from our study, however, is that patients with a family history of psychosis had a trend towards higher tHcys values. A potentially important cause of elevated Hcys levels is mutation in the genes encoding for enzymes in Hcys metabolism, especially the C677C N T polymorphism in the methylene-–tetrahydrofolate reductase (MTHFR) gene. Indeed, increased risk of schizophrenia has been associated with the high Hcys levels seen in individuals with homozygous genotypes of MTHFR 677C N T and A1298C transition [35–38], although not consistently [39–41]. Although this study did not specifically assess MHTFR polymorphisms, previous reports suggest that the prevalence of these mutations is generally lower in Arab than in Caucasian populations [42–45]. Nonetheless, the finding here, of a trend towards higher Hcys levels in SZ patients with a family history of psychosis raises the possibility of a genetic contribution to the association of Hcys with SZ, which warrants further detailed investigation. Homocysteine levels in SZ patients (but not HC) correlated significantly positively with BMI and serum TG levels and negatively with serum HDL levels. These biochemical and anthropometric parameters are components of the metabolic syndrome that confer increased susceptibility to atherosclerotic heart disease [46] and could possibly reinforce the enhanced atherogenic risk already ascribed to hyper-homocysteinaemia [7–9]. It may also at least partially explain the observation that atherosclerotic cardiovascular disease is a major cause of comorbidity and mortality in schizophrenia [47–49]. There are suggestions that the pathogenetic relationship between Hcys and SZ may be mediated by the role of Hcys in the damage to neuronal DNA with enhancement of apoptosis and increased sensitivity to excitotoxicity [50]. Indeed, oral methionine loading was reported to exacerbate schizophrenia symptomatology probably due to its conversion to Hcys [51– 53], and, in an animal model, oral homocysteine loading produced behavioural abnormalities [16]. An important strength of this study is the relatively large number of subjects with the statistical power to make appropriate inferences. The study was also longitudinal and prospective in that the patients had been carefully followed up for at least one year, such that the diagnosis of schizophrenia was confirmed in all cases. We believe that our results are valid because all the patients were very carefully reviewed with a rigid protocol by a psychiatrist and a standardized treatment protocol was used throughout. We also had the advantage of a relatively homogeneous racial and ethnic group that was well matched in social-economic status. Conclusion Plasma levels of homocysteine are increased in Arab patients with schizophrenia. Younger male patients had the highest levels, and those with a family history of psychosis also tended

to have high values. Other clinical parameters such as age of onset, disease severity, catatonia and negative symptomatology did not appear to be related to Hcys levels. These observations suggest that that there may be a role for oxidative stress, as indicated by Hcys levels, in the genesis and expression of schizophrenia. Acknowledgments This study was supported by a Kuwait University Research Administration grant no. MG 02/02. We acknowledge the technical expertise of Dr. Tarrik Zaid, Mr. PK Shihab and Ms. Arpita Bhattacharya. The following individuals also played an invaluable role in psychiatric data collection: Anila Jacob, Maha El-Taiyebani, Hani El-Shamali, Mohammed El-Dadiri, Rekha Kumar and Fabine James. Statement on financial disclosure/conflict of interest: Nil. References [1] el-Hilu SM, Mousa R, Abdulmalek H, Kamel N, Zohdi M, al-Aamriti M. Psychiatric morbidity among foreign housemaids in Kuwait. Int J Soc Psychiatry 1990;36:291–9. [2] al-Ansari EA, Emara MM, Mirza IA, el-Islam MF. Schizophrenia in ICD10: a field trial of suggested diagnostic guidelines. Compr Psychiatry 1989 (Sep.-Oct.);30(5):416–9. [3] Malasi TH, Mirza IA, el-Islam MF. Factors influencing long-term psychiatric hospitalisation of the elderly in Kuwait. Int J Soc Psychiatry 1989;35:223–30. [4] Chen JY, Hong CJ, Chiu HJ, Lin CY, Bai YM, Song HL, et al. Apolipoprotein E genotype and schizophrenia. Neuropsychobiology 1999; 39(3):141–3. [5] Fan X, Pristach C, Liu EY, Freudenreich O, Henderson DC, Goff DC. Elevated serum levels of C-reactive protein are associated with more severe psychopathology in a subgroup of patients with schizophrenia. Psychiatry Res 2007;149:267–71. [6] Zhang XY, Zhou DF, Zhang PY, Wu GY, Cao LY, Shen YC. Elevated interleukin-2, interleukin-6 and interleukin-8 serum levels in neurolepticfree schizophrenia: association with psychopathology. Schizophr Res 2002;57(2):247–58. [7] Kaul S, Zadeh AA, Shah PK. Homocysteine hypothesis for atherothrombotic cardiovascular disease: not validated. J Am Coll Cardiol 2006; 48(5):914–23. [8] Hankey GJ. Is plasma homocysteine a modifiable risk factor for stroke? Nat Clin Pract Neurol 2006;2(1):26–33. [9] Kannel WB. Overview of hemostatic factors involved in atherosclerotic cardiovascular disease. Lipids 2005;40(12):1215–20. [10] Clarke R, Smith AD, Jobst KA, Refsum H, Sutton L, Ueland PM. Folate, vitamin B12, and serum total homocysteine levels in confirmed Alzheimer's disease. Arch Neurol 1998;55:1449–55. [11] McCaddon A, Davies G, Hudson P, Tandy S, Cattell H. Total serum homocysteine in senile dementia of Alzheimer type. Int J Geriatr Psychiatry 1998;13:235–9. [12] Seshadri S, Beiser A, Selhub J, Jacques PF, Rosenberg IH, D'Agostino B, et al. Plasma homocysteine as a risk factor for dementia and Alzheimer's disease. N Engl J Med 2002;346:476–83. [13] Ramakrishnan S, Sulochana KN, Lakshmi S, Selvi R, Angayarkanni N. Biochemistry of homocysteine in health and diseases. Indian J Biochem Biophys 2006;43:275–83. [14] Regland B, Johansson BV, Grenfeldt B, Hjelmgren LT, Medhus M. Homocystinemia is a common feature of schizophrenia. J Neural Transm 1995;100:165–9. [15] Lerner V, Miodownik C, Kaptsan A, Vishne T, Sela BA, Levine J. High serum homocysteine levels in young male schizophrenic and

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