Homocysteine and Carotid Intima-Media Thickness in a German Population
Lack of Clinical Relevance
Background and Purpose— Common carotid artery intima-media thickness (CCA IMT) is a predictor of stroke. This study aimed to analyze whether homocysteine (Hcys) metabolism influences CCA IMT.
Methods— We analyzed the association of personal, clinical, and biochemical data (multivariate analysis) and of 9 polymorphisms involved in Hcys metabolism (ANOVA) with CCA IMT in 714 individuals of 187 families.
Results— CCA IMT was significantly predicted by age, sex, creatinine levels, lipoprotein(a) levels, pack-years of smoking, the presence of hypertension, and the presence of diabetes mellitus but not by Hcys levels. Homozygosity for the T allele of the polymorphism methylenetetrahydrofolate reductase c.677C>T was significantly associated with higher Hcys levels but not with a higher CCA IMT.
Conclusions— These data do not support the thesis that elevated Hcys levels are causally involved in cerebrovascular disease.
Within an ongoing study, we have previously reported that common carotid artery intima-media thickness (CCA IMT) is strongly influenced by genetic determinants other than the known classic risk factors.1 Because CCA IMT is a good indicator of early systemic atherosclerosis and of future stroke as well as myocardial infarction, CCA IMT is a promising candidate for genetic studies that aim to identify susceptibility genes for atherosclerosis.1 This study aimed to analyze the impact of plasma homocysteine (Hcys) levels and of 9 polymorphisms influencing Hcys metabolism for CCA IMT.
Subjects and Methods
From the ultrasound division of the Department of Neurology, we recruited 187 (mean±SD age, 64.3±8.8 years; 28% female) of 323 consecutive white patients who had been referred owing to vascular events like stroke (n=101), transient ischemic attack (n=93), coronary heart disease (n=64), myocardial infarction (n=37), or arterial occlusive disease (n=28). The inclusion criterion was at least unilateral carotid stenosis of 30% or higher. In addition, we recruited the included patients’ partners if they had no history of vascular events (n=139; mean±SD age, 61.5±8.8 years; 81% female) and all common children (n=388; mean±SD age, 36.2±8.1 years, 52% female). In summary, this study included 714 individuals. Personal data, CCA IMT, and additional clinical and laboratory parameters, including fasting plasma total Hcys, were determined as previously described.1
Genomic DNA was prepared from peripheral leukocytes to analyze the following polymorphisms: cystathionine β-synthase c.833T>C (I278T) and c.844_855ins68 (change of transcript levels); dihydrofolate reductase c.594+59del19bp (change of transcript levels); glutathione S-transferase Ω-1 c.428C>A (A140D); methylenetetrahydrofolate reductase (MTHFR) c.677C>T (A222V) and c.1298A>C (E429A); methyltetrahydrofolate homocysteine S-methyltransferase c.2756A>G (D919G); reduced folate carrier 1 c.80G>A (R27H); and transcobalamin 2 (Tc2) c.776C>G (P259R).2–6
The prediction of CCA IMT by vascular risk factors was analyzed by linear-regression analysis. The association of polymorphisms with CCA IMT and Hcys levels was analyzed by ANOVA with threshold of α=0.001 for multiple testing. The study was approved by the local ethics committee, and all subjects gave informed, written consent.
CCA IMT was significantly predicted by age, plasma levels of creatinine and lipoprotein(a), pack-years of smoking, male sex, and the presence of hypertension and of diabetes but not by Hcys levels (Table 1). Also, in separate analyses of patients, partners, and children and in subgroups of patients divided by type of vascular event, Hcys levels did not predict CCA IMT. Furthermore, in ANOVA analysis, CCA IMT did not significantly differ between individuals (all/patients/partners/children) with Hcys levels of the highest quartile in comparison with those individuals with Hcys levels of the lowest quartile (not shown). Because there is a direct correlation between Hcys levels and renal function, we performed an additional explorative analysis from which creatinine was omitted, but Hcys levels were still no significant predictor of CCA IMT (B=0.003, P=0.594).
The analyzed polymorphisms did not significantly influence CCA IMT (Table 2). However, only the MTHFR c.677C>T polymorphism influenced Hcys levels with borderline significance (mean±SD): 12.90±4.01 for CC, 13.65±4.00 for CT, and 15.20±5.37 μmol/L for TT (unadjusted ANOVA: F=6.37, P=0.002). The other polymorphisms were without significant effects, and there were no significant differences between patients, partners, and children (not shown). Furthermore, logistic-regression analysis with all vascular risk factors as covariables did not reveal an independent predictive character of Hcys levels for the dependent variable “patient” versus “partner” (B=0.004, P=0.444).
The present study aimed to analyze whether Hcys levels or polymorphisms involved in Hcys metabolism independently influence CAA IMT, which is an established early indicator of systemic atherosclerosis preceding stroke and myocardial infarction.1 We investigated 714 individuals of 187 families ascertained by an index patient with proven carotid atherosclerosis. Careful data stratification was performed in multivariate analysis. We did not find a significant prediction of CCA IMT by Hcys level either in all individuals or in the subgroups of patients, partners, and children. Hcys levels did not significantly predict vascular events (represented by membership in the group of patients versus partners), although such comparison was limited owing to differences between those groups and clinical heterogeneity within the patient group. Concerning the polymorphisms, the MTHFR c.677TT genotype was significantly associated with higher Hcys levels, as expected from the literature, but in contrast, not with higher CCA IMT.
Current studies controversially discuss whether elevated Hcys levels are only a secondary phenomenon of vascular events like stroke.7–9 In the Vitamin Intervention for Stroke Prevention (VISP) study, elevated baseline Hcys levels at the time of first stroke contributed a significant risk for recurrent stroke. However, multivitamin treatment to lower plasma Hcys did not prevent recurrent stroke.8 Taken together with our data, indicating that Hcys levels and polymorphisms involved in homocysteine metabolism also have no significant causal effect on early atherosclerosis preceding stroke and myocardial infarction, this supports the contention that plasma Hcys levels are confounded with other stroke risk factors, although it remains uncertain what these factors are. The intake of folate, which is important for Hcys levels, may be a candidate.9 The influence of the MTHFR c.677TT genotype remains undefined, but any putative effect seems considerably weaker than those of the classic risk factors. Thus, screening for increased Hcys levels or the MTHFR genotype in clinical routine may not be warranted.
We thank the patients and their families who made this study possible. The excellent technical assistance of M. Keller is gratefully acknowledged. We thank Dr Y. Smulders (Free University Medical Center, Department of Internal Medicine, Amsterdam, Netherlands) for fruitful discussions.
Source of Funding
This study was supported by a local university grant Bonfor (to C. Pohl).
- Received April 14, 2006.
- Accepted June 15, 2006.
Moskau S, Golla A, Grothe C, Boes M, Pohl C, Klockgether T. Heritability of carotid artery atherosclerotic lesions: an ultrasound study in 154 families. Stroke. 2005; 36: 5–8.
Johnson WG, Stenroos ES, Spychala JR, Chatkupt S, Ming SX, Buyske S. New 19 bp deletion polymorphism in intron-1 of dihydrofolate reductase (DHFR): a risk factor for spina bifida acting in mothers during pregnancy? Am J Med Genet A. 2004; 124: 339–345.
Kolsch H, Linnebank M, Lutjohann D, Jessen F, Wullner U, Harbrecht U, Thelen KM, Kreis M, Hentschel F, Schulz A, von Bergmann K, Maier W, Heun R. Polymorphisms in glutathione S-transferase Ω-1 and AD, vascular dementia, and stroke. Neurology. 2004; 63: 2255–2260.
Toole JF, Malinow MR, Chambless LE, Spence JD, Pettigrew LC, Howard VJ, Sides EG, Wang CH, Stampfer M. Lowering homocysteine in patients with ischemic stroke to prevent recurrent stroke, myocardial infarction, and death: the Vitamin Intervention for Stroke Prevention (VISP) randomized controlled trial. JAMA. 2004; 291: 565–575.