关键词： 同型半胱氨酸；MTHFR基因；原发性高血压；病例对照研究

摘要：目的：探讨升高的同型半胱氨酸水平、MTHFR基因突变与原发性高血压的关系。方法：从上海一个社区中随机选取127例35～75岁的原发性高血压病人和170例 正常血压者。采用聚合酶链反应-限制性片段长度多态性分析MTHFR基因多态性。使用高效液相色谱结合电化学方法检测血清中同型半胱氨酸总浓度，使用放射免疫法同时测定血清中叶酸和B₁₂浓度。结果：调整年龄和性别后，病例和对照组同型半胱氨酸水平分别为10.56 μmol /L 和 10.34 μmol/L，差异无显著性 (P=0.63)。在未服降压药的对象中同型半胱氨酸浓度与收缩压和舒张压亦无关联。该人群MTHFR不耐热性基因突变频率为13.1%，突变等位基因频率为38.7%。病例组与对照组基因型分布和突变等位基因频率无显著性差异。然而，病例组叶酸和B₁₂浓度高于对照组。结论：本研究未发现升高的同型半胱氨酸水平、MTHFR基因突变是原发性高血压的独立危险因素。高血压病人较高的叶酸和B₁₂水平可能降低了同型半胱氨酸的危险性。

分类号：R753;R544.1文献标识码：A

文章编号：1006-2866(2000)01-0021-02

Elevated serum homocysteine,MTHFR gene mutation and essential

hypertension in Chinese

ZHAN SiyanGAO YuanyuanYIN XiangjunHU YonghuaLEE Liming（Department of Epidemiology,School of Public Health,Beijing Medica l University,100083 P.R.China）

vivian NgLi EllenOng CN（Department of Community,Occupational and Family Medicine,the National University of Singapore,Singapore）

ABSTRACT：Objective: To examine the relationship between elevated homocyst eine levels,mut ation of the MTHFR 677 C to T and essential hypertension in a Chinese population,a commu nity-based case-control study was conducted.Methods: 127 essential hypertension patients of age 35 to 75 were ra ndomly selected from a community. 170 control subjects with blood pressure ＜140/90 mmHg were selected from the same community. MTHFR genotypes were identified by PCR and restriction fragm ent length polymorphism analysis with Hinf I digestion. Serum homocysteine was dete rmined using HPLC. Folate and vitamin B₁₂ were measured by radioimmunoassay.Results:After adjusting for age and sex,the mean homocysteine leve l was 10.56 μmol/L for hypertensive patients and 10.34μmol/L for controls (P=0.63). No associatio n between either SBP or DBP and Hcy concentration was found in subjects without anti-hype rtensive medications. The prevalence of homozygousity for thermolabile MTHFR variant for this population was 13.1%,and the mutant allele frequency was 38.7%. There was no significant difference on genotype distributions and the mutant allele frequency for two groups studied. However,the concentrations of folate and B₁₂ for the hyper tensive subjects were generally higher than the controls.Conclusions:The present study didn't find that elevated Hcy levels or MTHFR mutation are independent risk factors for essential hypertension. The higher folate and B ₁₂ in the hypertensive subjects might contribute to lower the risk of homocysteine.

Key Words：homocysteine;MTHFR;hypertension;case-co ntrol study▲

Recent epidemiological studies have suggested that mild and moderate elevation of plasma homocysteine (Hcy) level is an independent risk factor for atheroscleroti c vascular disease^［1～3］,although the mechanism remains unknown. Several studies a lso reported that there was a positive association between Hcy levels and SBP and/or DBP^{［4～9 ］},and suggested that atherogenesis could be due to the elevations of blood pressure.8 However, other studies were not able to find any correlation between elevated Hcy level and hypertensio n^{［10～12］}.Hcy is formed from methionine during transmethylation. It is remethylated to methionine by folate dependent 5-methyltetrahydrofolate-reductase (MTHFR) with vitamin B₁₂ as a cofactor. Defect of the MTHFR gene and/or deficiency of folate and B₁₂,may lead to the accumulation of Hcy in tissues and blood^［13］. Recent findin gs have indicated that mutation of the MTHFR thermolabile gene may affect the Hcy metabolism^{［14～1 6］} and thus is believed to involve in vascular diseases^［17］. To our knowledge,studies on MTHFR mutation and hypertension were rare and the results are confusing. Wilcken et al reporte d that the MTHFR mutation was weakly associated with hypertension (P=0.036) in Australi a Caucasians^［18］. In contrast,Adam et al showed that there was an increa sing trend towards a higher prevalence of hypertension in subjects with normal allele^［19］. O thers studies found no relationship between the MTHFR gene mutation and hypertension^{［20～22］}. Nevertheless,it is necessary to mention that in most of these studies factors that might affect Hcy level,such as folic acid and B₁₂,were not examined. In addition,age and gender,which are known to affect Hcy level were not taken into account.The present community-based study was carried out with an aim to examine the relationship between elevated Hcy levels,mutation of the MTHFR 677 C→T and e ssential hypertension of a Chinese population.

Methods

Study Population:

This investigation is part of a Community-based Comprehensive studies on Prevention And Control of Hypertension Project in China (CCPACH),over five year s from 1997 to 2001. The aim is to seek the most feasible preventive measures against cardiovascular disease in the People's Republic of China. The present study was conducted in an urban community,Nanshi District,in Shanghai,China. This district has a total population of about 60,000 residents. All residents of age 35 to 75 and who have lived at least 5 years in this community were randomly selected for investigation. Blood pressure was measured for all studied subjects. Subject with blood pressure ≥140/90 mm Hg (WHO criterion for hypertension) at the first screening was re-measured again after two weeks. If the subject's blood pressure was still ≥140/90 mmHg at the second screening or is currently under antihypertensive medications,they were classified as "hypertensive".For the present study,127 hypertensive cases were randomly selected from the residents of a Street in Nanshi District. 170 subjects were also randomly drawn from the normotensive (BP＜140/90 mmHg) population in the same community as controls.

None of the participants in this study had BP≥210/120 mmHg. Persons with rece nt myocardial infarction,stroke,uncontrolled angina for the past 3 months and sev ere liver or renal diseases were excluded from the study. Demographic data such as lifestyle, family history and history of diseases were obtained through interview during the surve y. Height and weight were also measured.

10 ml of venous blood samples was obtained from every subject in the morning aft er overnight fasting. Serum was separated within 45 minutes and stored at -20℃. Packed cells were also stored at 20℃. The study protocol was approved by the Ethics Committee of Beijing Medical University and informed consents were given by all participan ts.

Biochemical Analysis:

Serum Hcy was determined using high-performance liquid chromatography with electrochemical detection,a modified method of Smolin et al^［23］. In bri ef,50 μL of serum was mixed sequentially with 50 μL of water,150 μL of 9 mol/L urea and 25 μL of n -amylalcohol and 25 μL of 10% (w