Normalization of hyperhomocysteinemia with L-thyroxine in hypothyroidism

The role of non-invasive oscillometric method to detect aortic stiffness in patients with subclinical hypothyroidism

INTRODUCTION

Subclinical hypothyroidism (SCH) is a biochemical condition that is diagnosed when peripheral free thyroid hormone levels are within normal reference laboratory range but serum thyroid-stimulating hormone (TSH) levels are mildly elevated. The aim of this study was to investigate the relationship between SCH and arterial stiffness using two different non-invasive methods, including echocardiography and oscillometric arteriography.

MATERIAL AND METHODS

The study included 33 newly diagnosed SCH patients and 34 age- and gender-matched healthy controls. Systolic and diastolic diameters and elastic parameters of the aorta were calculated by 2D Transthoracic echocardiography (TTE). Central blood pressure and aortic stiffness values of patient groups were measured noninvasively from the brachial artery using Mobil-O-Graph arteriography. Pulse wave velocity (PWV) and augmentation index (AIx) were used as arterial stiffness indicators.

RESULTS

There was no significant difference between SCH and control groups with regard to age, gender, and body mass index (BMI). Aortic strain and aortic distensibility, were significantly lower in the SCH group than in the control group (p < 0.001). PWV and AIx which measured by Mobil-O-Graph arteriography were found to be significantly higher in the subclinical hypothyroid group compared to the control group (p < 0.05).

CONCLUSION

Aortic stiffness assessed by TTE and Mobil-O-Graph arteriography deteriorated in patients with SCH after excluding other cardiovascular risk factors. The assessment of aortic stiffness by the oscillometric method was easy and useful for widespread clinical use.

Homocysteine-a retrospective and prospective appraisal

The biologically important amino acid homocysteine links sulfur, methionine, and one-carbon metabolism. This review describes its initial discovery, the identification of the clinical condition of "homocystinuria" and the recognition of its close relationship to folate and vitamin B12 metabolism. It discusses the history behind its current association with diverse diseases including neural tube defects, cardio- and cerebrovascular disease and, more recently, dementia and Alzheimer's Disease. It also explores current controversies and considers potential future research directions. It is intended to give a general overview of homocysteine in relation to health and disease.

ARTERIAL WALL STIFFNESS AND THE RISK OF ATHEROSCLEROSIS IN EGYPTIAN PATIENTS WITH OVERT AND SUBCLINICAL HYPOTHYROIDISM

Objective: Hypothyroidism is associated with an increased risk of atherosclerosis. Pulse wave velocity (PWV) is an index of arterial wall stiffness widely used for noninvasive assessment of early atherosclerosis. We assessed PWV in Egyptian patients with hypothyroidism. Methods: The study included 100 Egyptian females aged 18 to 55 years. They were classified into three groups: group I, 40 women with overt hypothyroidism; group II, 40 women with subclinical hypothyroidism; and group III, 20 euthyroid women as a control group. The three groups were age matched. Doppler ultrasonography was used to calculate the heart-femoral PWV. Results: PWV was significantly higher in women with overt and subclinical hypothyroidism as compared with the control group (9.55 ± 1.81 m/s and 9.30 ± 1.28 m/s, respectively vs. 7.82 ± 2.14 m/s; P<.001 and <.01, respectively). There was a positive correlation between thyroid-stimulating hormone (TSH) and PWV in women with overt hypothyroidism and in those with subclinical hypothyroidism (P<.05 for both). Multivariate regression analysis showed that age and diastolic blood pressure were independent determinants of PWV in women with overt and subclinical hypothyroidism (P<.01 for all). TSH was also an independent determinant of PWV in both groups (P<.05 for both). Conclusion: PWV is significantly higher in Egyptian women with overt and subclinical hypothyroidism as compared with normal control subjects. This denotes early increase in arterial wall stiffness in patients with hypothyroidism, even in the subclinical phase. The positive correlation between PWV and TSH in both groups of patients suggests that the risk of atherosclerosis is proportionate to the severity of hypothyroidism. Abbreviations: ABI = ankle/brachial index; baPWV = brachial-ankle pulse wave velocity; BP = blood pressure; CIMT = carotid intima-media thickness; ECG = electrocardiogram; FT4 = free thyroxine; HDL = high-density lipoprotein; hfPWV = heart-femoral pulse wave velocity; LDL = low-density lipoprotein; PTT = pulse transit time; PWV = pulse wave velocity; SCH = subclinical hypothyroidism; TSH = thyroid-stimulating hormone.

The impact of autoimmune thyroiditis on skin microcirculation in children with non-complicated type 1 diabetes mellitus

BACKGROUND

The impairment of endothelial function in type 1 diabetes mellitus (DM1) is considered as the basis of microvascular complications. In DM1 patients autoimmune thyroiditis is a frequent comorbidity which may be responsible for further deterioration of microcirculation function. In studies investigating the relationship between cardiovascular risk factors and microvascular function, skin microcirculation is widely used. The aim of our study was to evaluate the impact of coexisting autoimmune thyroiditis on skin microcirculation in children with type I diabetes mellitus.

SUBJECTS

The study group consisted of 25 pediatric DM1 patients, 25 pediatric patients with type 1 diabetes and autoimmune thyroiditis (DM1 + AIT) and 29 control subjects matched for age and gender. The DM1 and DM1 + AIT patients were also matched for age at onset of DM and diabetes duration.

METHODS

Performed capillaroscopy studies employed non-selective stimuli such as post-occlusive reactive hyperemia (PORH) and venous occlusion (VO) tests. The relative area covered by capillaries (coverage) and the distance between capillaries were assessed. These measurements were performed before tests as well as after PORH and VO.

RESULTS

Coverage at baseline, after PORH and VO and distance after VO differ significantly between control subjects and the group DM1 + AIT. The coverage at baseline, after PORH and VO were significantly smaller in DM1 + AIT compared with the control group. Post-hoc analysis after controlling for lipids levels showed that differences between the DM1 + AIT and control group were remained only for coverage at baseline and after VO. Significant differences between DM1 + AIT and DM1 and control group for coverage after VO were also presented.

CONCLUSIONS

Coexisting autoimmune thyroiditis significantly deteriorates skin microcirculation function in pediatric non-complicated type 1 diabetic patients. This process is independent of patient age, diabetes duration and age of diabetes onset.

Biomarkers of Nutrition for Development (BOND): Vitamin B-12 Review

This report on vitamin B-12 (B12) is part of the Biomarkers of Nutrition for Development (BOND) Project, which provides state-of-the art information and advice on the selection, use, and interpretation of biomarkers of nutrient exposure, status, and function. As with the other 5 reports in this series, which focused on iodine, folate, zinc, iron, and vitamin A, this B12 report was developed with the assistance of an expert panel (BOND B12 EP) and other experts who provided information during a consultation. The experts reviewed the existing literature in depth in order to consolidate existing relevant information on the biology of B12, including known and possible effects of insufficiency, and available and potential biomarkers of status. Unlike the situation for the other 5 nutrients reviewed during the BOND project, there has been relatively little previous attention paid to B12 status and its biomarkers, so this report is a landmark in terms of the consolidation and interpretation of the available information on B12 nutrition. Historically, most focus has been on diagnosis and treatment of clinical symptoms of B12 deficiency, which result primarily from pernicious anemia or strict vegetarianism. More recently, we have become aware of the high prevalence of B12 insufficiency in populations consuming low amounts of animal-source foods, which can be detected with ≥1 serum biomarker but presents the new challenge of identifying functional consequences that may require public health interventions.

Serum levels of nitrite/nitrate, lipid profile, and Fasting Plasma Glucose and their associations in subclinical hypothyroid women before and after a two month treatment by levothyroxine

BACKGROUND

Subclinical hypothyroidism (sHT) is a condition defined by elevated TSH values with normal levels of free thyroid hormones. Altered metabolic status is one of the consequences of sHT which can affect serum levels of FPG, lipid profile, and nitric oxide which propounds cardiovascular consequences per se. The aim of this study was to determine the possible effects of sHT on nitrite/nitrate levels, as a marker of endothelial performance.

MATERIALS AND METHODS

50 females were enrolled in this study, 25 women as control group and 25 women as case group (evaluated two times: before and after levothyroxine therapy). Blood samples were collected and levels of FPG, lipid profile components, and nitric oxide were measured spectrophotometrically. The data were analyzed using SPSS version 18 software.

RESULTS

The levels of lipid profile (except for TG between before and after group, p < 0.05) and nitric oxide did not differ in groups while FPG was significantly higher in case groups in comparison to control group (p < 0.001). Nitric oxide had no correlations with any of variables except for LDL in after treatment group (p < 0.05 and r = 0.397).

CONCLUSION

Nitric oxide does not have correlation with components of lipid profile (except for LDL) or FPG and has no differences in subclinical hypothyroid patients and control group. Levothyroxine therapy during 2 months cannot alter the levels of nitric oxide in subclinical hypothyroid patients.

Effects of levothyroxine treatment on insulin sensitivity, endothelial function and risk factors of atherosclerosis in hypothyroid women

OBJECTIVES

Contradictory results are encountered in literature regarding the effects of hypothyroidism on the risk factors of atherosclerosis. We aimed to explore the changes in atherosclerotic risk factors and insulin sensitivity before and after levothyroxine replacement therapy in women with primary hypothyroidism and compare with that of healthy controls.

PATIENTS AND METHODS

Twelve patients (mean age of 34±11.7years) without an evident disease except for primary hypothyroidism (TSH≥20mIU/L) and eleven euthyroid, age-matched (33.8±8.4years) female volunteers as controls were included. Baseline thyroid hormones, lipid parameters, homocysteine, fibrinogen levels were measured in both groups. Flow-mediated endothelial-dependent vasodilatation (FMD) method was used to evaluate endothelial dysfunction. Insulin sensitivity was assessed by M values based on euglycemic hyperinsulinemic clamp technique. The same measurements were performed after 6months of levothyroxine treatment and recovery of euthyroid state in hypothyroid patients.

RESULTS

Treatment reduced total cholesterol (P<0.005), LDL-cholesterol (P<0.005), lipoprotein(a) (P<0.01), fibrinogen (P<0.0001) and homocysteine (P<0.0005) levels. Treatment significantly improved M values of hypothyroid patients (3.68±1.53mg/kg.min vs 6.02±1.21mg/kg.min, P<0.0001) and FMD (9.1±3.7% vs 16.4±4.4%, hypothyroid vs euthyroid, P<0.0001). Significant correlations were found between M values and TSH (r=-0.6, P<0.005), fibrinogen (r=-0.53, P<0.01) measurements, free T3 (r=0.51, P<0.02) and free T4 (r=0.49, P<0.02) levels. FMD was significantly correlated with fibrinogen levels (r=-0.49, P<0.05).

CONCLUSION

Insulin resistance, endothelial dysfunction, atherosclerotic risk markers improves with treatment of hypothyroidism.

Effect of leucovorin (folinic acid) on the developmental quotient of children with Down's syndrome (trisomy 21) and influence of thyroid status

Background

Seven genes involved in folate metabolism are located on chromosome 21. Previous studies have shown that folate deficiency may contribute to mental retardation in Down's syndrome (DS).

Methodology

We investigated the effect of oral folate supplementation (daily dose of 1.0±0.3 mg/kg) on cognitive functions in DS children, aged from 3 to 30 months. They received 1 mg/kg leucovorin or placebo daily, for 12 months, in a single-centre, randomised, double-blind study. Folinic acid (leucovorin, LV) was preferred to folic acid as its bioavailability is higher. The developmental age (DA) of the patients was assessed on the Brunet-Lezine scale, from baseline to the end of treatment.

Results

The intent-to-treat analysis (113 patients) did not show a positive effect of leucovorin treatment. However, it identified important factors influencing treatment effect, such as age, sex, and concomitant treatments, including thyroid treatment in particular. A per protocol analysis was carried out on patients evaluated by the same examiner at the beginning and end of the treatment period. This analysis of 87 patients (43 LV-treated vs. 44 patients on placebo) revealed a positive effect of leucovorin on developmental age (DA). DA was 53.1% the normal value with leucovorin and only 44.1% with placebo (p<0.05). This positive effect of leucovorin was particularly strong in patients receiving concomitant thyroxin treatment (59.5% vs. 41.8%, p<0.05). No adverse event related to leucovorin was observed.

Conclusion

These results suggest that leucovorin improves the psychomotor development of children with Down's syndrome, at least in some subgroups of the DS population, particularly those on thyroxin treatment.

Trial Registration

ClinicalTrials.gov, NCT00294593

Association between vitamin B12-containing supplement consumption and prevalence of biochemically defined B12 deficiency in adults in NHANES III (third national health and nutrition examination survey)

OBJECTIVE

To explore the association between vitamin B(12) (B(12))-containing supplement use, low B(12) concentrations and biochemically defined B(12) deficiency in US adults.

DESIGN

A cross-sectional study with adjustment for survey design. Prevalence ratios for two age groups (18-50 and >50 years) were estimated using unconditional logistic models. Outcome measures included prevalence of low serum B(12) concentration (<148 pmol/l) and biochemical B(12) deficiency (serum B(12)< 148 pmol/l with concomitant homocysteine > 10 mumol/l).

SETTING

A population survey of health and nutritional measures.

SUBJECTS

Subjects were non-institutionalized adults, aged 18 years and older, who participated in Phase 2 of NHANES III (Third National Health and Nutrition Examination Survey).

RESULTS

Low B(12) concentrations were less prevalent among persons consuming B(12)-containing supplements (P = 0.001) with an adjusted prevalence ratio of 0.6 (95 % CI 0.3, 1.0). Biochemical B(12) deficiency showed a similar trend (P = 0.0002), with an adjusted prevalence ratio of 0.3 (95 % CI 0.1, 0.8). Prevalence ratios were similar in adults >50 years of age, although the prevalence of low B(12) and biochemical deficiency was proportionally higher.

CONCLUSIONS

Consumption of B(12)-containing supplements was associated with at least 50 % lower prevalence of both low serum B(12) and biochemical B12 deficiency in a nationally representative sample of US adults, suggesting increased consumption of B(12) from supplements or from fortified foods may reduce the prevalence of B(12) deficiency. Additionally, the current Recommended Daily Allowance for B(12) of 2.4 microg may be insufficient for those aged >50 years.

The effect of hormone replacement treatment on thrombin-activatable fibrinolysis inhibitor activity levels in patients with Hashimoto thyroiditis

BACKGROUND

Hypothyroid patients have increased risk of cardiovascular diseases, and several mechanisms have been considered responsible in these patients. Although, a few studies demonstrated fibrinolytic system changes in hypothyroid patients, there is no study demonstrating TAFI activity in hypothyroid Hashimoto's thyroiditis patients. The aim of this study was to evaluate TAFI activity status and the effect of L thyroxin hormone replacement treatment on fibrinolytic system in this patient group.

METHODS

Thirty patients with hypothyroid Hashimoto thyroiditis (all were female and the mean age was 44.3+/-14.6 years, ranging between 17-68 years) were enrolled to study. Their TSH levels were high (27.2+/-5.2 mU/L) and Free T3 and Free T4 hormone levels were below than normal. In this study, euthyroid 20 healthy volunteers (mean age 32.5+/-4.9 years, range 26-42 years) were adopted. L-thyroxin treatment before and after TAFI activity levels were measured in patients.

RESULTS

In the control group, TAFI activity levels were 9.6+/-0.4 microg/mL. In patients with L-thyroxin before and after treatment there were high levels of TAFI activity value of 14.2+/-0.9 and 12.9+/-0.8 microg/mL, respectively. In the patient group, after L-thyroxin treatment TAFI activity levels were decreased but they were not statistically significant (p=0.187). When compared to the control group, high levels of TAFI activity were observed in the patient group (p<0.0001).

CONCLUSION

Our data demonstrated that in Hashimoto thyroiditis, patients have high levels of TAFI activity compared to controls. A high level of TAFI activity suggests fibrinolytic deficit or thrombotic tendency in hypothyroid patients and this deficit is persistent after L-thyroxine replacement.

Subclinical hypothyroidism, hyperhomocysteinemia and dyslipidemia: investigating links with ischemic stroke in Turkish patients

OBJECTIVES

Hyperhomocysteinemia is a risk factor for ischemic stroke. Hypothyroidism may cause hyperhomocysteinemia. To date, no works have examined the association between hypothyroidism and hyperhomocysteinemia in ischemic stroke. We aimed to investigate the roles of hypothyroidism and hyperhomocysteinemia in ischemic stroke, and whether any relationship exists between hypothyroidism and hyperhomocysteinemia in ischemic stroke patients.

METHODS

The study included 249 ischemic stroke patients and 102 patients with no history of stroke. Patients were evaluated for conventional risk factors and levels of homocysteine, thyroid-stimulating hormone, vitamin B12 and folic acid.

RESULTS

Ten (4%) patients in the ischemic stroke group had subclinical hypothyroidism. We did not find any overt or subclinical hypothyroidism in the control group. Hypothyroidism was higher to a statistically significant degree in the ischemic stroke group (p<0.05). Both hyperhomocysteinemia and hypothyroidism were associated with ischemic stroke patients. However, no association was found between hyperhomocysteinemia and hypothyroidism. Ischemic stroke patients with hypothyroidism had lower levels of HDL cholesterol and levels of total cholesterol/HDL-C and LDL-C/HDL-C were higher than those of ischemic stroke patients without hypothyroidism.

DISCUSSION

Hypothyroidism is associated with ischemic stroke. Low HDL cholesterol, high total cholesterol/HDL-C and high LDL-C/HDL-C were associated in ischemic stroke patients with hypothyroidism. Hyperhomocysteinemia was not found to be associated with ischemic stroke patients with hypothyroidism.

Coronary flow reserve after L-thyroxine therapy in Hashimoto's thyroiditis patients with subclinical and overt hypothyroidism

BACKGROUND/AIMS

Overt and subclinical hypothyroidism are reported to be associated with increased cardiovascular disease risk. We have used coronary flow reserve (CFR) measurement by trans-thoracic Doppler echocardiography (TTDE) to determine coronary microvascular function in Hashimoto's thyroiditis patients with overt and subclinical hypothyroidism and to evaluate effects of L-thyroxine replacement on coronary endothelial function.

METHODS

In total, 10 overt hypothyroid patients, 10 subclinical hypothyroid patients, and 10 controls were enrolled. FT4, TSH, anti-thyroid antibodies, lipid profile, insulin, glucose, HOMA-IR, physical parameters, and CFR measured by TTDE were recorded before and after 6 months of L: -thyroxine replacement in all groups.

RESULTS

CFR values of all hypothyroid patients at baseline were significantly lower than those in controls. After L: -thyroxine, CFR increased significantly in overt and subclinical hypothyroidism with respect to the baseline measurements (P < 0.05). When baseline and second measurements were evaluated collectively for patients and controls, CFR was positively correlated with FT4 levels (r = 0.31, P = 0.01) and negatively correlated with TSH and HOMA-IR (r = -0.38, P = 0.002 and r = -0.42, P < 0.001, respectively).

CONCLUSION

Subclinical as well as overt hypothyroid patients have impaired coronary microvascular function which improved after L: -thyroxine therapy. Treatment of Hashimoto's thyroiditis patients with subclinical hypothyroidism should be considered to improve cardiovascular disease risk.

Hypothyroidism

Hypothyroidism is one of the most common disorders encountered in an endocrine office practice. This article reviews the epidemiology, etiology, clinical presentation, diagnosis, and treatment of hypothyroidism. We emphasize some of the more recent issues, such as combination thyroid hormone therapy, management of hypothyroidism during pregnancy, and the management of subclinical hypothyroidism.

Homocysteine and fibrinogen changes with L-thyroxine in subclinical hypothyroid patients

The aim of the present study was to evaluate plasma total homocysteine (Hcys) and serum fibrinogen concentrations in subclinical hypothyroid (SH) and overt hypothyroid patients before and after L-thyroxine (LT4) replacement and to compare them in euthyroid subjects. Fifteen SH and 20 hypothyroid premenopausal women were recruited in the study. We measured fasting plasma levels of Hcys and serum levels of free thyroxine (fT4), free triiodothyronine (fT3), thyrotropin (TSH), folate, vitamin B12, fibrinogen, renal functions, and lipid profiles in patients with SH and overt hypothyroid patients before and after LT4 treatment. Eleven healthy women were included in the study as a control group. Pretreatment Hcys levels were similar in SH and control subjects, whereas mean fibrinogen level of SH patients was higher than that of control subjects (p<0.05). Baseline Hcys (p<0.01) and fibrinogen (p<0.001) levels of the overt hypothyroid patients were significantly higher than those of the healthy subjects, and the pretreatment Hcys levels decreased with LT4 treatment (p<0.001). In conclusion, our data support that SH is not associated with hyperhomocysteinemia and Hcys does not appear to contribute to the increased risk for atherosclerotic disease in patients with SH.

Interaction of plasma homocysteine and thyroid hormone concentrations in the pathogenesis of the slow coronary flow phenomenon

BACKGROUND AND OBJECTIVE

The slow coronary flow (SCF) phenomenon is an angiographic observation and a well-recognized clinical entity characterized by delayed opacification of vessels in a normal coronary angiogram due to reasons yet unclear. Thyroid hormones exert significant effects on plasma homocysteine (Hcy) levels and microvascular resistance. Recently, several investigators have consistently reported that elevation of the plasma Hcy level can severely disturb vascular endothelial function and play a role in the pathogenesis of SCF. Accordingly, we investigated the levels of plasma Hcy and thyroid hormones and their relationship in patients with SCF.

METHOD

Forty-four patients with angiographically proven SCF (Group I) (mean age 55.5 +/- 10.4 years, 26 males) and 44 cases with normal coronary flow (NCF) pattern (Group II) (mean age 53.9 +/- 11 years, 22 males) with similar risk profiles were enrolled in the study. Coronary flow patterns of the cases were determined by the thrombolysis in myocardial infarction (TIMI) frame count method. The coronary TIMI frame counts were calculated separately for each coronary artery and their average was determined as the mean TIMI frame count for each subject. Serum levels of free tri-iodothyronine (fT3), free thyroxine (fT4), thyroid stimulating hormone (TSH) and Hcy were measured. Patients with thyroid disease or on medications with a potential to affect thyroid functions were excluded.

RESULTS

There were no statistically significant differences between the groups concerning the demographic characteristics and major cardiovascular risk factors. Mean TIMI frame counts of SCF and NCF groups were 45.9 +/- 12 and 23.3 +/- 3.7, respectively. fT4 (ng/dl) and TSH (microIU/ml) levels of the two groups were similar (p > 0.05). The level of fT3, the active metabolite of the thyroid hormone family, was dramatically reduced in the SCF group when compared to the NCF group (2.3 +/- 0.2 vs. 3.0 +/- 0.3, p = 0.0001, respectively). Plasma Hcy levels of patients with SCF were found to be significantly higher than controls (12.2 +/- 4.9 vs. 8.5 +/- 2.9, p = 0.0001, respectively). Correlation analysis showed a significant negative correlation between the plasma fT3 and Hcy levels and the mean TIMI frame counts (r = -0.31, p = 0.003 vs. r = -0.66, p = 0.0001). Moreover, there was a significant positive correlation between the plasma Hcy levels and the mean TIMI frame counts (r = 0.58, p = 0.0001). Also, fT3 was the only significant determinant of the variance of Hcy in multiple regression analysis (r = -0.30, p = 0.005).

CONCLUSION

fT3 levels were decreased and plasma Hcy levels were increased significantly in patients with SCF as compared to controls. This finding suggests that thyroid hormones and/or (?) a possible disturbance in their metabolism may be responsible for the elevated levels of plasma Hcy in patients with SCF and may play a role in the pathogenesis of the SCF phenomenon.

Polymorphism C776G in the transcobalamin II gene and homocysteine, folate and vitamin B12 concentrations. Association with MTHFR C677T and A1298C and MTRR A66G polymorphisms in healthy children

One of the etiologies of hyperhomocysteinemia is decreased vitamin B(12). Genetic variation in the transcobalamin II gene, the transporter of vitamin B(12) to the cells, may produce altered homocysteine levels. We determined transcobalamin II C776G polymorphism, homocysteine, folate and vitamin B(12) levels and analyzed the interactive effect with the methylenetetrahydrofolate reductase C677T and A1298C and methionine synthase reductase A66G polymorphisms in 207 healthy Brazilian children. The prevalence of GG genotype of transcobalamin II C776G polymorphism in this Brazilian population, a highly miscigeneous population was 12.5% and the statistical analysis showed that this population is in Hardy-Weinberg equilibrium, it could be considered representative of the general population. We observed a significant increase in homocysteine in the 776GG vs. 776CC genotype, corroborating the influence of age as a determinant of homocysteine in relation to this polymorphism. When we analyzed vitamin B(12) and its relationship with the C776G polymorphism, we found no significant differences. Only 776CG/66AA or 776GG/66AG genotypes presented a significant increase in homocysteine when compared with other groups. In the multivariate analysis, transcobalamin II C776G (CC/CG vs. GG), methylenetetrahydrofolate reductase C677T (CC/CT vs. TT), folate, gender and age presented statistical significance in relation to the homocysteine. These can be considered independent risk factors for hyperhomocysteinemia in this children group. Our results, if confirmed in other populations, highlight the necessity for investigation of the transcobalamin II C776G polymorphism in the research for hyperhomocysteinemia risk factors.

Abnormal endothelial function in female patients with hypothyroidism and borderline thyroid function

BACKGROUND

It has been suggested that hypothyroidism is associated with an increased risk for cardiovascular disease. The aim of this study was to assess non-invasively NO-dependent endothelial function of resistance arteries in subjects with hypothyroidism of varying severity.

METHODS

Ninety-six female subjects (aged: 42+/-13 years) comprised the study population. Subjects were divided into five groups based on TSH levels at presentation: Group 0 (n=23) with TSH: 0.3-2.0 microU/ml, Group 1 (n=22) with TSH: 2.1-4.0 microU/ml (upper normal), Group 2 (n=18) with TSH: 4.1-10 microU/ml (subclinical hypothyroidism), Group 3 (n=22) with TSH >10 microU/ml (overt hypothyroidism). One additional group with well-controlled hypothyroidism on L-thyroxine therapy (Group 4, n=11, TSH: 0.3-2.0 microU/ml) was also studied. Endothelial function of resistance arteries was assessed by measuring forearm blood flow response during reactive hyperemia utilizing venous occlusion strain-gauge plethysmography.

RESULTS

Duration of reactive hyperemia was significantly different among groups of subjects with varying hypothyroidism (83.7+/-58.3 s, 53.2+/-35.7 s, 52.8+/-47.5 s, 12.9+/-13.3 s and 69.5+/-26.2 s in Groups 0, 1, 2, 3 and 4, respectively, p<0.001, ANOVA). Duration of reactive hyperemia was significantly shorter in subjects with upper normal TSH values (Group 1) compared to controls (53.2+/-35.7 s vs. 83.7+/-58.3 s, p=0.013), while it was comparable to that of subjects with subclinical hypothyroidism (Group 2) (52.8+/-47.5 s). However, duration of reactive hyperemia in Group 1 was significantly longer compared to Group 3 (overt hypothyroidism) (53.2+/-35.7 s vs. 12.9+/-13.3 s, p=0.002). Similarly, duration of reactive hyperemia in subjects with subclinical hypothyroidism was significantly longer compared to subjects with overt hypothyroidism (52.8+/-47.5 s vs. 12.9+/-13.3 s, p=0.003). Duration of reactive hyperemia in Group 4 (well-controlled hypothyroidism on L-thyroxine therapy) did not differ significantly compared to controls. There was a highly significant linear correlation between duration of reactive hyperemia and TSH (r=-0.383, p<0.001).

CONCLUSION

Endothelial dysfunction was detected in the microvasculature of patients with hypothyroidism. Duration of reactive hyperemia decreased with increasing TSH levels. Since endothelial dysfunction is a factor leading to atherosclerosis, this abnormality may partly explain predisposition of patients with thyroid failure to cardiovascular disease.

Restoration of euthyroidism does not improve cardiovascular risk factors in patients with subclinical hypothyroidism in the short term

Subclinical hypothyroidism (SH) is being accepted as a condition that is associated with increased risk of cardiovascular disease. Restoration of euthyroidism might be involved in prevention of cardiovascular disease. Thus, we evaluated biochemical risk factors of 75 patients with SH without evidence of any other diseases before and after restoration of euthyroidism and compared to 27 healthy controls. Before and a mean of 18.2+/-4.4 weeks after restoration of euthyroidism, serum total and LDL cholesterol, lipoprotein (Lp) (a), total homocysteine (t-Hyc) and highly sensitive C-reactive protein (hsCRP) levels were analyzed. Pre-treatment levels of TSH (10.04+/-5.36 vs 1.74+/-1.1 mIU/l, p<0.05), total cholesterol (204+/-68 vs 179+/-26 mg/dl, p<0.05) and LDL cholesterol (129+/-50 vs 106+/-16 mg/dl, p<0.05) were significantly higher than controls while Lp (a), t-Hyc, and hsCRP levels were not different. None of these biochemical risk factors have improved after euthyroidism in patients with SH with average dose of 85+/-30 microg/day, when compared to pre-treatment levels. Only in a subgroup of patients (no. 30) with higher TSH levels (>10 mIU/l), did serum LDL cholesterol levels decrease significantly (139+/-38 vs 112+/-35 mg/dl, p<0.05). Lp (a), t-Hyc and hsCRP levels were not significantly different after treatment with levothyroxine therapy even in this subgroup of patients. We conclude that clinical management of SH does not contribute to prevention of cardiovascular disease in the short term, and monitoring risk factors of cardiovascular disease does not offer additional benefits for treating patients with SH.

Which thyroid-stimulating hormone level should be sought in hypothyroid patients under L-thyroxine replacement therapy?

We sought to determine whether relationships exist between level of thyroid-stimulating hormone (TSH) suppression and cardiovascular risk parameters such as plasma homocysteine, C-reactive protein (CRP), fibrinogen, D-dimer and serum cholesterol in patients taking L-thyroxine-replacement therapy (LT4-RT). Four hundred and two hypothyroid patients under LT4-RT were cross-sectionally evaluated. Patients were grouped according to their achieved TSH (mIU/l) levels under LT4-RT on an arbitrary manner. Those patients having a TSH value 0.4-2 were defined as group 1 (n = 154), a TSH level of 2 to less than 5.5 were defined as group 2 (n = 176) and a TSH level of 5.5 to less than 20 with a normal free T3 and free T4 level were defined as group 3 (n = 72). The three groups of patients were also compared with overt hypothyroid patients (n = 71) and healthy controls (n = 97). Homocysteine levels (micromol/l) were significantly different between the three groups (10.4 +/- 4 for group 1, 11.3 +/- 3.7 for group 2 and 13.5 +/- 4.7 for group 3; p < 0.01 for all groups). Significant differences in CRP (mg /l) levels were present between the three groups (2.6 +/- 2.6 for group 1, 3.3 +/- 2.9 for group 2 and 4.8 +/- 4.1 for group 3; p < 0.01 for all groups). Univariate analysis showed that both homocysteine and CRP levels significantly correlated with free T4 and TSH level (p < 0.01 for both groups). No statistically significant differences were noticed in respect to fibrinogen and d-dimer levels between three groups. In examining the effect of LT4-RT on lipid parameters, a tendency towards beneficial effects without achieving statistical significance was observed. Practically speaking, a target TSH level of less than 2 might be advisable to lower CRP levels and homocysteine levels, and possibly lipid parameters.

Impact of renal function or folate status on altered plasma homocysteine levels in hypothyroidism

Hyperhomocysteinemia is an independent risk factor for coronary, peripheral and cerebrovascular diseases. Moderately elevated total homocysteine (tHcy) levels have been reported in patients with overt hypothyroidism. Plasma tHcy concentration is affected by several physiological factors and is elevated under conditions of impaired folate and cobalamin status and in renal failure. The aim of this study was to assess plasma tHcy concentrations and to evaluate the role of potential determinants of plasma tHcy levels in hypothyroid patients. Fasting plasma tHcy, serum homocysteine-related vitamins folate and vitamin B(12), serum cystatin C (CysC) and creatinine, were determined in 22 hypothyroid patients and compared with 25 healthy control subjects. Creatinine clearance (CCr) was calculated using the Cockroft-Gault formula. Plasma tHcy levels were determined by HPLC with fluorescence detection and serum CysC by automated particle enhanced immunoturbidimetry. Plasma tHcy, creatinine levels were significantly higher, and serum CysC levels, and creatinine clearance values were lower in hypothyroid patients than in control subjects. Folate levels were lower in hypothyroidic group compared to the control group. There were no differences in vitamin B(12) levels between hypothyroid and control groups. Positive correlation was noted between tHcy and creatinine levels in hypothyroid patients (r = 0.596); however, an inverse correlation was found between tHcy and folate levels (r = -0.705) in hypothyroid patients. In conclusion, tHcy was increased in hypothyroidism, and this increase was more strongly associated with changes in serum folate than in serum creatinine and CysC, suggesting an altered folate status.

Impending cardiac tamponade as a primary presentation of hypothyroidism: case report and review of literature

OBJECTIVE

To describe a patient who presented with pericardial effusion and impending cardiac tamponade attributable to hypothyroidism.

METHODS

We present clinical, laboratory, and imaging data for the current patient and review the literature relative to clinical presentation, prevalence, pathophysiology, diagnosis, and treatment of pericardial effusion and tamponade.

RESULTS

In comparison with previously reported cases, our current case is rare, in that our patient, a 51-year-old woman, presented with impending cardiac tamponade as an initial manifestation of hypothyroidism. Echocardiography demonstrated a large pericardial effusion and diastolic right atrial collapse. A pericardial window procedure was performed, and 1,500 mL of fluid was removed. Levothyroxine therapy was initiated. One month later, recurrent pericardial effusion necessitated a similar intervention, after which the patient recovered and was managed by outpatient follow-up and monitoring of the thyrotropin level.

CONCLUSION

From our review of the literature, we conclude that impending cardiac tamponade is a rare initial manifestation of hypothyroidism. A high index of suspicion must be maintained for timely diagnosis of pericardial tamponade followed by prompt intervention. Recurrent pericardial effusions are common, necessitating close follow-up. Treatment of the hypothyroidism with levothyroxine is imperative.

Does Treating Subclinical Hypothyroidism Improve Markers of Cardiovascular Risk?

Subclinical hypothyroidism is defined as an elevated serum thyroid-stimulating hormone (TSH) level in the face of normal free thyroid hormone values. The overall prevalence of subclinical hypothyroidism is 4-10% in the general population and up to 20% in women aged >60 years. The potential benefits and risks of therapy for subclinical hypothyroidism have been debated for 2 decades, and a consensus is still lacking. Besides avoiding the progression to overt hypothyroidism, the decision to treat patients with subclinical hypothyroidism relies mainly on the risk of metabolic and cardiovascular alterations. Subclinical hypothyroidism causes changes in cardiovascular function similar to, but less marked than, those occurring in patients with overt hypothyroidism. Diastolic dysfunction both at rest and upon effort is the most consistent cardiac abnormality in patients with subclinical hypothyroidism, and also in those with slightly elevated TSH levels (>6 mIU/L). Moreover, mild thyroid failure may increase diastolic blood pressure as a result of increased systemic vascular resistance. Restoration of euthyroidism by levothyroxine replacement is generally able to improve all these abnormalities. Early clinical and autopsy studies had suggested an association between subclinical hypothyroidism and coronary heart disease, which has been subsequently confirmed by some, but not all, large cross-sectional and prospective studies. Altered coagulation parameters, elevated lipoprotein (a) levels, and low-grade chronic inflammation are regarded to coalesce with the hypercholesterolemia of untreated patients with subclinical hypothyroidism to enhance the ischemic cardiovascular risk. Although a consensus is still lacking, the strongest evidence for a beneficial effect of levothyroxine replacement on markers of cardiovascular risk is the substantial demonstration that restoration of euthyroidism can lower both total and low-density lipoprotein-cholesterol levels in most patients with subclinical hypothyroidism. However, the actual effectiveness of thyroid hormone substitution in reducing the risk of cardiovascular events remains to be elucidated. In conclusion, the multiplicity and the possible reversibility of subclinical hypothyroidism-associated cardiovascular abnormalities suggest that the decision to treat a patient should depend on the presence of risk factors, rather than on a TSH threshold. On the other hand, levothyroxine replacement therapy can always be discontinued if there is no apparent benefit. Levothyroxine replacement therapy is usually safe providing that excessive administration is avoided by monitoring serum TSH levels. However, the possibility that restoring euthyroidism may be harmful in the oldest of the elderly population of hypothyroid patients has been recently raised, and should be taken into account in making the decision to treat patients with subclinical hypothyroidism who are aged >85 years.

The role of homocysteine in multisystem age-related problems: a systematic review

Homocysteine is a sulfur-containing amino acid that is involved in one-carbon metabolism. Hyperhomocysteinemia is a common phenomenon among elderly people. There is growing evidence of an association between hyperhomocysteinemia and geriatric multisystem problems, including coronary artery disease, stroke, peripheral vascular disease, cognitive impairment, dementia, depression, osteoporotic fractures, and functional decline. The proposed mechanisms of the association include angiotoxicity, neurotoxicity, and inhibition of collagen cross-linking. A homocysteine-lowering strategy may prevent or slow the development of these age-related problems. Vitamin supplementation and folic acid fortification of grain foods have been shown to decrease plasma homocysteine concentrations. More research is needed to investigate whether lifelong homocysteine lowering can prevent the development of late-life morbidity.

Thyroid diseases and cerebrovascular disease

BACKGROUND AND PURPOSE

Acute cerebral ischemia has been described in different diseases of the thyroid gland, and not only as a result of thyrotoxic atrial fibrillation and cardioembolic stroke. The purpose of this review is to summarize the studies on the relationship between thyroid diseases and cerebrovascular diseases, discussing the main findings for overt hyperthyroidism and hypothyroidism, as well as for subclinical thyroid dysfunction.

SUMMARY OF REVIEW

In overt hyperthyroidism, cardioembolic stroke is clearly associated to thyrotoxic atrial fibrillation, and in subclinical hyperthyroidism with serum thyroid-stimulating hormone levels <0.1 mU/L, the incidence of atrial fibrillation is increased. Although in vitro and in vivo studies indicate a hypercoagulability state in hyperthyroidism, there is insufficient evidence to prove that this state leads to an increased risk of cardiac emboli. However, the hypothesis that overt hyperthyroidism may cause acute cerebral venous thrombosis is intriguing. Possible associations between hyperthyroidism and Moyamoya or Giant cell arteritis have only been described in case reports. There is enough evidence that overt hypothyroidism is associated with several traditional and newer atherosclerotic risk factors, especially hypertension, hyperlipidemia, and hyperhomocysteinemia. For subclinical hypothyroidism, these associations are less certain. Hypothyroidism has been associated with signs of aortic or coronary atherosclerosis, but no case-control or cohort studies have ever investigated hypothyroidism as a possible risk factor for atherothrombotic stroke.

CONCLUSIONS

Hyperthyroidism is associated with atrial fibrillation and cardioembolic stroke. Hypothyroidism is associated with a worse cardiovascular risk factor profile and leads to progression of atherosclerosis. Associations between hyperthyroidism and acute cerebral venous thrombosis, Moyamoya, and Giant cell arteritis have been suggested, but sound evidence is lacking. Additional studies are needed to clarify these issues.

Arterial stiffness is increased in subjects with hypothyroidism

BACKGROUND

The association between hypothyroidism and increased vascular resistance, arterial wall thickening and endothelial dysfunction is well recognized. The aim of the present study was to examine if hypothyroid subjects have increased arterial stiffness, a risk factor for cardiovascular morbidity and mortality.

METHODS

Sixty-five subjects (59 females and 6 males) with normal thyroid function or hypothyroidism of varying degree were investigated by radial artery applanation tonometry and pulse wave analysis, for evaluation of arterial stiffness.

RESULTS

Serum TSH values were positively correlated with central systolic blood pressure (r=0.258, p=0.037), central pulse pressure (r=0.316, p=0.010), augmentation pressure (r=0.299, p=0.015) and negatively with reflection time index (RTI), which indicates the pressure wave velocity (r=-0.311, p=0.012). Hypothyroid patients presented higher central systolic pressure and pulse pressure, higher augmentation pressure and lower RTI, indicating increased arterial stiffness in these subjects. RTI was independently related to age, central systolic pressure and TSH. Mild changes of arterial stiffness were observed even in subjects with TSH range 2.01-4.0 muU/ml suggesting that this group may have an early stage of mild thyroid failure.

CONCLUSIONS

Hypothyroidism, even in the subclinical stage, is associated with changes in arterial stiffness. The observed abnormalities in arterial stiffness may have detrimental effects on left ventricular function and coronary perfusion in hypothyroid subjects.

Antiphospholipid antibodies and thrombosis: association with acquired activated protein C resistance in venous thrombosis and with hyperhomocysteinemia in arterial thrombosis

Although antiphospholipid antibodies (aPL) are associated with thrombosis, it is not known who with aPL is at higher risk for thrombosis. It was the aim of this cross-sectional study to investigate how thrombophilic factors contribute to venous or arterial thrombosis in aPL-positive individuals. In outpatient test centres at two tertiary care hospitals, two hundred and eight (208) persons requiring aPL testing were matched by age, gender and centre to 208 persons requiring a complete blood count. Persons were classified as aPL-positive (having anticardiolipin, lupus anticoagulant and/or anti-beta(2)-glycoprotein I antibodies) or aPL-negative. Several thrombophilic factors were studied using logistic regression modelling. Results showed that the aPL-positive group had three-fold more events (37%) than the aPL-negative group (12%). In unadjusted analyses, clinically important associations were observed between factor V Leiden and venous thrombosis, hyperhomocysteinemia and arterial thrombosis, and activated protein C resistance (APCR) and venous thrombosis (OR, 95% CI = 4.00, 1.35-11.91; 4.79, 2.03-11.33; and 2.03, 1.03-3.97, respectively). After adjusting for recruitment group, persons with both APCR and aPL had a three-fold greater risk (OR, 95% CI = 3.31, 1.30-8.41) for venous thrombosis than those with neither APCR nor aPL. Similarly, after adjusting for hypertension, family history of cardiovascular disease, gender and recruitment group, persons with both hyperhomocysteinemia and aPL had a five-fold increased risk (OR, 95% CI = 4.90, 1.37-17.37) for arterial thrombosis compared to those with neither risk factor. In conclusion, APCR phenotype and hyperhomocysteinemia are associated with a higher risk of venous and arterial thrombosis, respectively, in the presence of aPL.

Methimazole-induced hypothyroidism paradoxically decreases homocysteine

Clinical hypothyroidism is associated with hyperhomocysteinemia, whereas the opposite is seen in hyperthyroidism. The effects of mild thyroid dysfunction on homocysteine concentrations are not known. We performed the following study to investigate this. Total homocysteine, vitamins B6 and B12, folate, fibrinogen, plasminogen activator inhibitor type 1, and lipids were measured in 11 subjects at baseline and after methionine loading. Subjects began methimazole (MMI), 40 mg daily, and were restudied during 2 stages of hypothyroidism. Liothyronine was added and subjects were restudied once thyrotropin normalized. Methimazole was stopped and studies were repeated during 2 stages of hyperthyroidism. Data were analyzed using repeated-measures analysis of variance. Post-methionine homocysteine decreased in each hypothyroid study compared with baseline (28.8+/-10.7, 27.5+/-9.9 vs 34.4+/-9.2 micromol/L, respectively). In addition, both fasting and post-methionine homocysteine decreased in the euthyroid/MMI study arm compared with baseline despite equivalent thyrotropin values (fasting, 7.5+/-3.0 vs 8.8+/-3.5 micromol/L, P<.05; and post-methionine, 27.2+/-10.6 vs 34.4+/-9.2 micromol/L, P<.05, respectively). Fasting homocysteine decreased in the first hyperthyroidism study arm compared with baseline (6.6+/-2.3 vs 8.8+/-3.5 micromol/L, P<.05) and post-methionine homocysteine decreased in both hyperthyroid arms compared with baseline (25.2+/-8.1, 24.2+/-10 vs 34.4+/-9.2 micromol/L, P<.05 respectively). In conclusion, mild thyroid dysfunction changes homocysteine metabolism. Unexpectedly, our results suggest a homocysteine-lowering effect of MMI.

Thyroid, hemostasis and thrombosis

The aim of this paper is to briefly review some practical aspects of the relationship between thyroid function and several disorders of the hemostatic system in terms of bleeding and thrombosis. Thrombocytopenia, acquired hemophilia, hypercoagulability, cardioembolism and other biochemical coagulative and fibrinolytic abnormalities have been described in the past years both in hyper- and hypothyroidism. Since most of hyper- and hypothyroid conditions are the consequence of autoimmune thyroid disease (1), either deranged immune function, altered circulating thyroid hormone concentration, or both may concur in the pathogenesis of hemostatic disorders of potential crucial clinical impact. These aspects will be outlined and discussed in an attempt to give answers to some questions, often arising in the clinical approach.

Emerging cardiovascular risk factors in subclinical hypothyroidism: lack of change after restoration of euthyroidism

Subclinical hypothyroidism (SH) is a frequent condition that may be associated with increased cardiovascular risk. There is current interest in determining the effect, if any, of substitutive therapy with l-thyroxine (L-T4) on cardiovascular risk factors in SH and, particularly, on those associated with emerging cardiovacular risk, such as apolipoprotein (apo) B, lipoprotein (Lp) (a), total homocysteine (t-Hcy), and C-reactive protein (CRP). Thus, the aim of this study was to assess the impact of euthyroidism restoration on these emerging risk factors in SH. Forty-two patients diagnosed with SH were consecutively recruited before treatment. These patients were treated with L-T4 for 3 to 6 months with the dose necessary to restore euthyroidism. Lp(a), fasting and postmethionine (n = 28) t-Hcy, and CRP did not change with substitutive therapy, regardless of the respective baseline values, and the decrease in apo B paralleled that of low-density lipoprotein (LDL) cholesterol. Similarly, no treatment effect was observed on homocysteine or CRP in patients with thyrotropin-stimulating hormone (TSH) >10 mIU/L. Monitoring of emerging risk factors did not offer additional arguments for treating patients with SH and, thus, is not justified in their clinical management.

Is Subclinical Hypothyroidism Associated With Hyperhomocysteinemia?

OBJECTIVE

To evaluate whether subclinical hypothyroidism is associated with hyperhomocysteinemia, in an attempt to determine whether hyperhomocysteinemia may explain the observed increased risk of coronary artery disease in patients with subclinical hypothyroidism, as has been shown in patients with overt hypothyroidism.

METHODS

We prospectively enrolled consecutive patients with newly diagnosed subclinical hypothyroidism and a parallel group of euthyroid control subjects in this study. Subclinical hypothyroidism was defined as high thyrotropin and normal free thyroxine levels. Fasting plasma total homocysteine, thyrotropin, and free thyroxine levels were measured in all participants, and persistent subclinical hypothyroidism was confirmed at least once.

RESULTS

Forty-seven patients (42 women and 5 men; mean age, 38 +/- 15 years) with subclinical hypothyroidism and 50 control subjects (46 women and 4 men; mean age, 34 +/- 10 years) were enrolled in the study. The manufacturer's reference range for the total homocysteine assay was 5 to 15 micromol/L, and we defined our own reference range as 3.9 to 10.8 micromol/L. The mean values (+/-SE) for total homocysteine in patients and control subjects were 7.44 +/- 0.5 micromol/L and 7.22 +/- 0.2 micromol/L, respectively (P = 0.68).

CONCLUSION

In this study, we found no association between subclinical hypothyroidism and hyperhomocysteinemia. Other contributing factors, such as associated hyperlipidemia, may explain the observed increased risk of coronary artery disease in patients with subclinical hypothyroidism.

Homocysteine concentrations in subclinical hypothyroidism

Hyperhomocysteinemia is considered to be an independent risk factor for atherosclerotic heart disease, including coronary artery disease (CAD). It is already known that overt hypothyroidism gives rise to a slight hyperhomocysteinemia. However, the effects of subclinical hypothyroidism on the levels of homocysteine are not known. In this study, we have evaluated homocysteine levels and the effect of L-thyroxine treatment in patients with subclinical hypothyroidism. For the purpose of the study, we selected 33 women patients with the diagnosis of subclinical hypothyroidism but without clinical CAD. After a euthyroidism development period of almost four months, a further study was done on patients who had been treated with thyroid hormone. The patient group was compared with 25 healthy control female subjects who were of similar age. In the patient group, homocysteine levels prior to treatment were significantly higher than in the control group (P < 0.001). After L-thyroxine treatment, homocysteine levels were reduced significantly. In summary, we found that homocysteine levels were in the normal range in subclinical hypothyroidism. However, when compared with the healthy control group, the difference between them was significant. On the other hand, therapy to produce euthyroidism caused a significant reduction in homocysteine levels.

Hypothyroidism as a risk factor for cardiovascular disease

The cardiovascular risk in patients with hypothyroidism is related to an increased risk of functional cardiovascular abnormalities and to an increased risk of atherosclerosis. The pattern of cardiovascular abnormalities is similar in subclinical and overt hypothyroidism, suggesting that a lesser degree of thyroid hormone deficiency may also affect the cardiovascular system. Hypothyroid patients, even those with subclinical hypothyroidism, have impaired endothelial function, normal/depressed systolic function, left ventricular diastolic dysfunction at rest, and systolic and diastolic dysfunction on effort, which may result in poor physical exercise capacity. There is also a tendency to increase diastolic blood pressure as a result of increased systemic vascular resistance. All these abnormalities regress with L-T4 replacement therapy. An increased risk for atherosclerosis is supported by autopsy and epidemiological studies in patients with thyroid hormone deficiency. The "traditional" risk factors are hypertension in conjunction with an atherogenic lipid profile; the latter is more often observed in patients with TSH >10 mU/L. More recently, C-reactive protein, homocysteine, increased arterial stiffness, endothelial dysfunction, and altered coagulation parameters have been recognized as risk factors for atherosclerosis in patients with thyroid hormone deficiency. This constellation of reversible cardiovascular abnormalities in patient with TSH levels <10 mU/L indicate that the benefits of treatment of mild thyroid failure with appropriate doses of L-thyroxine outweigh the risk.

Population-based differences in frequency of the transcobalamin II Pro259Arg polymorphism

OBJECTIVE

A common polymorphism of the transcobalamin II (TC-II) gene, Pro250Arg, has been implicated as a possible genetic factor in population-based differences in vitamin B(12) metabolism. Our objective was to determine whether the prevalence of TC-II Pro259Arg polymorphism differs significantly between Caucasian, Asian and African-American groups.

METHODS

Genomic DNA was available on 187 Caucasians and 43 Asians from the Toronto area, and 51 African-Americans from Northeastern United States. A mutagenically separated PCR method was employed to genotype these groups for the TC-II Pro259Arg polymorphism (776C-->G).

RESULTS

The frequency of the Arg 259 allele varied significantly among the three groups studied (0.439 in Caucasian, 0.558 in Asian and 0.363 in African; P = 0.022). The Asian group had a significantly higher frequency of the Arg 259 allele compared to the Caucasian (P = 0.030) and the African-American group (P = 0.006). The frequency of the Arg 259 allele in the Caucasian and African-American groups was not significantly different (P = 0.103).

CONCLUSION

Population-based differences in TC-II Pro259Arg frequency are significant and could be a contributor to ethnic variation in susceptibility to vitamin B(12) deficiency, a common and persistent problem.

Homocysteine and its relation to B-vitamins in Graves' disease before and after treatment: effect modification by smoking

OBJECTIVES

To investigate plasma total homocysteine levels and its relation to B-vitamins and smoking in Graves' disease before and after antithyroid therapy.

DESIGN

A longitudinal study taking place at four hospitals in Norway.

METHODS AND SUBJECTS

Plasma total homocysteine, serum folate, serum cobalamin and riboflavin, flavin mononucleotide and flavin adenine dinucleotide in plasma were investigated in 182 patients with hyperthyroidism before treatment. The same parameters were reinvestigated in 112 of these patients after attaining euthyroid state.

RESULTS

In hyperthyroidism, plasma total homocysteine was low, and inversely related to folate, cobalamin and riboflavin, and positively related to serum creatinine and age. Following antithyroid therapy, total homocysteine increased and the concentration of folate, cobalamin, riboflavin, flavin mononucleotide and flavin adenine dinucleotide decreased significantly. The most pronounced reduction (35%) was observed for flavin mononucleotide. In the hyperthyroid state, smokers had lower levels of folate and flavin mononucleotide than non-smokers. After restoration of euthyroidism, both folate and riboflavin were significantly lower in smokers than non-smokers. Plasma total homocysteine increased according to decreasing quartiles of B-vitamins. For riboflavin, this relation was confined to smokers.

CONCLUSION

Plasma total homocysteine changes according to thyroid status. These changes may be partly attributable to altered folate, cobalamin but also riboflavin status, particularly in smokers.

Reduction of plasma homocysteine and serum methylmalonate concentrations in apparently healthy elderly subjects after treatment with folic acid, vitamin B12 and vitamin B6: a randomised trial

OBJECTIVES

To investigate, in an elderly population: (1) the effects of oral B-vitamin therapy on P-tHcys, S-MMA and Hb/MCV, (2) the appropriate decision limit for 'high' metabolite concentrations and (3) the estimated prevalence of vitamin B(12)/folate deficiency on the basis of different decision limits.

DESIGN

Double-blind placebo-controlled intervention study.

SETTING

Outpatient clinic.

SUBJECTS

A total of 209 community-dwelling subjects, median age 76 y (range 70-93) y.

INTERVENTION

Four months of oral daily supplementation with 0.5 mg cyanocobalamin, 0.8 mg folic acid and 3 mg vitamin B(6).

RESULTS

High P- tHcys was found in 64% of men and 45% of women, high S-MMA in 11% of both. Vitamin B(12) deficiency was observed in 7.2% and folate deficiency in 11% of all subjects. Health-related upper reference limits for the metabolites at the start were higher than the laboratory's upper reference limits. The latter were, however, similar to those of the vitamin replete group. There was a significant decrease in P-tHcys (P<0.001) and S-MMA (P=0.009) after 4 months of vitamin treatment. In a multivariate analysis, the P-Hcys change correlated positively with baseline P-tHcys and inversely with baseline P-folate and transferrin saturation (Fe/TIBC ratio). The S-MMA change correlated with baseline S-MMA and inversely with baseline vitamin B(12) and age.

CONCLUSIONS

Suboptimal vitamin status is an important cause of elevated P-tHcys and S-MMA in apparently healthy elderly subjects. Oral B-vitamin therapy is an effective and convenient way to normalise P-tHcys and S-MMA.

Potential Association of Thyrotoxicosis with Vitamin B and Folate Deficiencies, Resulting in Risk for Hyperhomocysteinemia and Subsequent Thromboembolic Events

OBJECTIVE

To describe a patient with severe thyrotoxicosis attributable to Graves' disease who had a thrombotic cerebrovascular accident and hyperhomocysteinuria, which resolved on correction of the thyrotoxicosis, and to present findings in a pilot study undertaken to investigate the relationship among thyrotoxicosis, homocysteine, folate, and vitamin B(12).

METHODS

We present a case report of the index case, with clinical and laboratory details. For the investigative analysis, 21 patients who were 18 to 50 years old and had newly diagnosed, untreated Graves' disease and 10 age-and sex-matched euthyroid control subjects were studied. Of the patients with Graves' disease, 11 underwent studies both at diagnosis and after treatment. Fasting blood tests were performed for thyrotropin, free thyroxine, homocys-teine, vitamin B(12), folate, and methylmalonic acid, a marker of vitamin B(12) deficiency.

RESULTS

Vitamin B(12), folate, homocysteine, and methylmalonic acid levels were not significantly different between the thyrotoxic and control or posttreatment groups. In patients with thyrotoxicosis, however, free thyroxine was positively correlated with both homocysteine (r = 0.67; P = 0.03) and methylmalonic acid (r = 0.89; P = 0.003).

CONCLUSION

The positive correlation between free thyroxine levels and both homocysteine and methylmalonic acid suggests that thyrotoxicosis may be associated with functional vitamin B(12) deficiency. Such a deficiency may result in clinically important hyperhomocysteine-mia.

Impact of subclinical hypothyroidism on serum total homocysteine concentrations, the prevalence of coronary heart disease (CHD), and CHD risk factors in the New Mexico Elder Health Survey

The serum/plasma total homocysteine (tHcy) concentration, now recognized as an independent risk factor for accelerated atherosclerotic disease, is increased in overtly hypothyroid patients, and it decreases with thyroid replacement therapy. Whether or not individuals with subclinical hypothyroidism also increase their tHcy concentrations, and whether this elevation might help to explain the increased prevalence of the atherosclerotic diseases observed in this condition, remains unclear. If individuals with subclinical hypothyroidism have higher tHcy concentrations than euthyroid subjects, there would be added incentive to treat this condition earlier. In this cross-sectional study (New Mexico Elder Health Survey) of a randomly selected sample of Medicare recipients (age > or =65 years), no significant difference in serum tHcy concentrations could be detected between the 112 participants with subclinical hypothyroidism (Groups 2 and 3) and the 643 participants with thyrotropin (TSH) values < or =4.6 microU/mL (Group 1) after adjusting for differences in gender, ethnicity, age, and serum concentrations of folate, vitamin B(12), and creatinine. Only those participants with the highest TSH levels (>10 microU/mL) (Group 3) had a significantly higher prevalence of coronary heart disease (CHD) when compared against Group 1 participants (p = 0.007). No consistent significant differences in the prevalences of CHD or in the CHD risk factors examined were observed when all participants with subclinical hypothyroidism (Groups 2 and 3 combined) were compared against Group 1 participants.

Elevated C-reactive protein and homocysteine values: cardiovascular risk factors in hypothyroidism? A cross-sectional and a double-blind, placebo-controlled trial

Hypothyroidism is associated with premature atherosclerosis and cardiovascular disease. Recently, total homocysteine (tHcy) and C-reactive protein (CRP) emerged as additional cardiovascular risk factors. We first investigated CRP and tHcy in different severities of primary hypothyroidism and in a second study we evaluated the effect of L-thyroxine treatment in patients with subclinical hypothyroidism (SCH) in a double-blind, placebo-controlled trial. One hundred and twenty-four hypothyroid patients (63 with subclinical, 61 with overt hypothyroidism, OH) and 40 euthyroid controls were evaluated. CRP was measured using a latex-based high sensitivity immunoassay; tHcy was determined by a fluorescence polarization immunoassay. tHcy values were significantly elevated in OH (P=0.01). In SCH tHcy levels were not augmented as compared to controls. CRP values were significantly increased in OH (P=0.016) and SCH (P=0.022) as compared to controls. In a univariate analysis tHcy correlated significantly with fT4, vitamin B12, folic acid and creatinine levels. In multiple regression analysis only fT4 (beta=0.33) had a significant effect on tHcy. CRP did not correlate with thyroid hormones. In SCH, L-T4 replacement had no significant effect on either tHcy or CRP levels. This is the first paper to show that CRP values increase with progressive thyroid failure and may count as an additional risk factor for the development of coronary heart disease in hypothyroid patients. In contrast to overt disease, only CRP, but not tHcy values, are affected in SCH, yet without significant improvement after L-thyroxine therapy.

Cardiovascular and medical ramifications of treatment of subclinical hypothyroidism

Subclinical hypothyroidism can be diagnosed in 1% to 10% of the adult population, is more common in women, and increases with age. In many patients, treatment with L-thyroxine reduces low-density lipoprotein cholesterol, improves cardiac function, reduces symptoms of hypothyroidism, and diminishes neuropsychiatric symptoms. Treatment also reduces the likelihood of statin-induced myopathy. However, in double-blind, placebo-controlled trials of L-thyroxine therapy in subclinical hypothyroidism, cardiovascular and symptomatic benefits have been neither uniform nor definitive. In the absence of a large-scale, multicenter, randomized trial, physicians have to individualize therapy for each patient. Benefits of therapy are most likely to be realized in patients with thyroid-stimulating hormone levels greater than 10 mU/L on repeated measures, those with hypothyroid symptoms, those who are pregnant, those with a documented family history of hypothyroidism, and those with severe hyperlipidemia.

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.

Pharmacotherapy of hyperhomocysteinaemia in patients with thrombophilia

Hyperhomocysteinaemia is often the result of inherited abnormalities of the enzymes involved in homocysteine metabolism or vitamin deficiencies (vitamins B12, B6 or folate) and is present in approximately 5% of the general population. High homocysteine levels in these individuals are associated with a significant increase in relative risk for both arterial and venous thromboembolic disease. Consequently, effective homocysteine-lowering therapeutic strategies have been extensively investigated. Folic acid represents the cornerstone of treatment. In daily doses of at least 0.4 mg, it effectively reduces homocysteine levels, even in non-folate-deficient patients. The addition of vitamins B12 and/or B6, to folic acid supplementation may provide a small further reduction in homocysteine levels in certain groups of patients. Renal impairment is an important cause of hyperhomocysteinaemia. Individuals with hyperhomocysteinaemia secondary to renal disease commonly require significantly higher doses of folic acid (5-40 mg) to achieve maximal therapeutic effect. The important question of whether effective homocysteine-lowering therapy translates into a reduction in vascular disease remains unknown but is being addressed in a series of ongoing prospective trials.

Homocysteine: a risk factor for cardiovascular disease in subclinical hypothyroidism?

The role of homocysteine as a causal risk factor for cardiovascular disease remains controversial. Moderately elevated total plasma homocysteine levels have been reported in patients with overt hypothyroidism, a condition that is associated with an increased risk for cardiovascular disease. Recently, subclinical hypothyroidism has been identified as an independent risk factor for atherosclerosis and myocardial infarction in elderly women. Therefore, we measured prospectively total fasting plasma homocysteine levels in 37 consecutive subjects (6 males, 31 females, mean age 50 +/- 18 standard deviation [SD] years) with newly diagnosed subclinical hypothyroidism at baseline and after 3-4 months of levothyroxine supplementation. During levothyroxine treatment concentrations of thyrotropin (TSH) decreased from 10.1 +/- 5.8 (SD) to 1.5 +/- 1.8 mU/L. Fasting total plasma homocysteine levels were not elevated at baseline (9.9 +/- 2.9 micromol/L) and remained unchanged (9.6 +/- 3.5 micromol/L) after levothyroxine treatment. Serum folate or vitamin B(12) levels also remained unchanged. We conclude that subclinical hypothyroidism is not associated with hyperhomocysteinemia. Levothyroxine supplementation has no influence on total plasma homocysteine levels in subclinical hypothyroidism. Hence, total plasma homocysteine does not appear to contribute to the increased risk for atherosclerotic disease and myocardial infarction in patients with subclinical hypothyroidism.

Hyperhomocysteinemia and thrombosis

Homocysteine (Hcy) is a sulfhydryl amino acid derived from the metabolic conversion of methionine, which is dependent on vitamins (folic acid, B12, and B6) as cofactors or cosubstrates. In 1969, McCully first reported the presence of severe atherosclerotic lesions in patients with severe hyperhomocysteinemia and hypothesized the existence of a pathogenic link between hyperhomocysteinemia and atherogenesis. Several case-control and cross-sectional studies were consistent with the initial hypothesis of McCully, showing that moderate hyperhomocysteinemia is also associated with heightened risk of occlusive arterial disease. Less consistent results have been reported by prospective cohort studies of subjects who were healthy at the time of their enrollment, whereas prospective cohort studies of patients with overt coronary artery disease or other conditions at risk consistently confirmed the association between moderate hyperhomocysteinemia and cardiovascular morbidity and mortality. More recently, an association between moderate hyperhomocysteinemia and heightened risk of venous thromboembolism has been documented, suggesting that hyperhomocysteinemia might be involved not only in atherogenesis, but also in thrombogenesis. The mechanisms by which hyperhomocysteinemia might contribute to atherogenesis and thrombogenesis are incompletely understood. The mainstay of treatment of hyperhomocysteinemia is folic acid, alone or in combination with vitamin B12 and vitamin B6. Although it is quite clear that vitamins effectively reduce the plasma levels of total homocysteine (tHcy), we do not yet know whether they will decrease the risk of vascular disease. The results of ongoing randomized, placebo-controlled, double-blind trials of the effects of vitamins on the thrombotic risk will help in defining whether the relationship between hyperhomocysteinemia and thrombosis is causal, and will potentially have a dramatic effect in the prevention of thromboembolic events.

Risk factors for cardiovascular disease in women with subclinical hypothyroidism

Overt hypothyroidism may result in accelerated atherosclerosis and coronary heart disease (CHD) presumably because of the associated hypertension, hypercholesterolemia, and hyperhomocysteinemia. As many as 10%-15% of older women have subclinical hypothyroidism (SH) and thyroid autoimmunity. Whether SH is associated with risk for CHD is controversial. We examined 57 women with SH and 34 healthy controls. SH was defined as an elevated thyrotropin (TSH) (>4.5 mU/L) and normal free thyroxine (FT(4)) level (8.7-22.6 nmol/L). None of the patients had been previously treated with thyroxine. In all participants we determined blood pressure, body mass index (BMI), and fasting TSH, FT(4), antibodies to thyroid peroxidase and thyroglobulin, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), triglycerides, folic acid, vitamin B(12), creatinine, and total plasma homocysteine levels. The SH and control groups did not differ in their total homocysteine values. Mean diastolic blood pressure was increased in SH patients versus controls (82 vs. 75 mm Hg; p < 0.01). Mean values of TC, HDL-C, LDL-C, triglycerides, TC/HDL-C, and LDL-C/HDL-C were not different in patients with SH compared with controls. Individual analysis revealed that the percentage of patients with SH having hypertension (20%), hypertriglyceridemia (26.9%), elevated TC/HDL-C (11.5%), and LDL-C/HDL-C (4%) ratios were higher than the percentages in controls. Hyperhomocysteinemia (> or = 10.98 micromol/L) was observed in 29.4% of SH and was not significantly different from the percentage in controls (21.4%). No significant correlation between TSH and biochemical parameters was detected. We conclude that subclinical hypothyroidism in middle-aged women is associated with hypertension, hypertriglyceridemia, and elevated TC/HDL-C ratio. This may increase the risk of accelerated atherosclerosis and premature coronary artery disease in some patients.

Hyperhomocysteinemia in patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL)

OBJECTIVE

To determine whether patients with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) had evidence of increased homocysteine levels compared with non-CADASIL patients with ischemic stroke or transient ischemic attack.

PATIENTS AND METHODS

We compared fasting plasma homocysteine levels and levels 6 hours after oral loading with methionine, 100 mg/kg, in non-CADASIL patients with ischemic stroke or transient ischemic attack and in patients with CADASIL. Prechallenge, postchallenge, and change in homocysteine levels between the 2 groups were compared with use of the Wilcoxon rank sum test.

RESULTS

CADASIL and non-CADASIL groups were similar in age (mean, 48.8 vs. 46.5 years, respectively; 2-tailed t test, P=.56) and sex (men, 86% vs 59%; Fisher exact test, P=.12). The 59 patients in the CADASIL group had higher median plasma homocysteine levels compared with the 14 patients in the non-CADASIL group, both in the fasting state (12.0 vs 9.0 micromol/L; P=.03) and after methionine challenge (51.0 vs 34.0 micromol/L; P=.007). Median difference between homocysteine levels before and after methionine challenge was greater in the CADASIL group than in the non-CADASIL group (34.5 vs. 24.0 micromol/ L; P = .02).

CONCLUSION

Our findings raise the possibility that increased homocysteine levels or abnormalities of homocysteine metabolism may have a role in the pathogenesis of CADASIL.