Clinical characteristics of H‐type hypertension and its relationship with the MTHFR C677T polymorphism in a Zhuang population from Guangxi, China

Abstract Objective This study was designed to assess the clinical presentation of patients with H‐type hypertension who were of Zhuang nationality in Guangxi, China. The relationship between the C677T polymorphism in the MTHFR gene and H‐type hypertension was also assessed. Methods This was a case‐control study in which 185 Zhuang nationality patients with hypertension that had been hospitalized at the Wuming Hospital of Guangxi Medical University between February 2018 and December 2018 were assessed for plasma homocysteine (Hcy) levels. These levels were used to divide patients into H‐type (>15 μmol/L) and non‐H‐type (≤15 μmol/L) hypertension groups. Patient clinical data were then analyzed, and PCR was used to analyze samples from all patients for the presence of the C677T polymorphism in the MTHFR gene. Differences between these two groups of hypertension patients were then compared using appropriate statistical methods. Results We found that relative to patients in the non‐H‐type hypertension group, patients in the H‐type hypertension group exhibited significant differences in sex, age, urea nitrogen levels, creatinine levels, and uric acid levels. There were, however, no significant differences between these two groups with respect to interventricular septum thickness, left ventricular posterior wall thickness, or ejection fraction. We did not detect any association between the MTHFR gene C677T polymorphism and H‐type hypertension in Zhuang nationality individuals in Guangxi. Conclusion Risk of H‐type hypertension is not associated with the MTHFR C677T polymorphism in hypertensive individuals of Guangxi Zhuang nationality in China.


| INTRODUC TI ON
H-type hypertension is a form of primary hypertension that also presents with hyperhomocysteinemia (HHcy). This condition is relatively common in mainland China and is associated with an elevated risk of stroke. 1 On average, adult Chinese patients with hypertension have plasma total homocysteine (tHcy) levels of ~15 mmol/L owing to environmental and genetic factors, with elevated plasma Hcy levels being evident in 75% of Chinese hypertension patients, including 91% of male and 63% of female patients. 2 In Chinese patients with hypertension, elevated Hcy levels are an independent risk factor for stroke. 3 According to previous studies, for every 5 mmol/L increase in tHcy, the chance of stroke increases by 59%. In addition, there appears to be a synergistic effect between HHcy and hypertension, both of which are associated with an increased risk of cardiovascular disease and stroke. 4 Elevated tHcy levels are usually caused by vitamin B deficiency, genetic variations, and a significant decrease in renal function. Of known tHcy genetic determinants, the C677T polymorphism of the methylenetetrahydrofolate reductase (MTHFR) gene is by far the most important and best-studied. [5][6][7] Methylenetetrahydrofolate reductase is a key regulator of Hcy levels, and the C677T mutation in this gene results in a sharp decline in Hcy activity. 8 The MTHFR C677T (rs1801133) mutation is relatively common and has been linked to increased blood pressure and hypertension in individuals carrying this mutation. 9,10 The Zhuang people are the largest minority group in China, and genotyping to determine whether they were carriers of the C677T polymorphism, and the relationship between this polymorphism and the abovementioned variables was also assessed.

| Study population
In total, 185 patients of Zhuang nationality with hypertension that chronic CVD, secondary hypertension, hypercalcemia, chronic cerebrovascular disease, pregnancy, and chronic liver or kidney disease.

The Ethics Committee of Guangxi Medical University approved
the study, and all participants provided consent to participate after being informed of the study protocol.

| Physical examination and laboratory analyses
Patient baseline demographic and clinical characteristics including sex, age, weight, and whether or not patients had been diagnosed with coronary heart disease, diabetes, or cerebral infarction were recorded. In order to measure blood pressure, patients were instructed to rest while for 5 minutes, after which a sphygmomanometer was used to determine blood pressure in the right arm. For blood collections, patients fasted overnight for a minimum of 12 hours, after which blood was collected for measurements of high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), creatinine, urea nitrogen, and uric acid. HDL-C and LDL-C were measured using an AU5800 autoanalyzer (Beckman Coulter).
Creatinine, urea nitrogen, and uric acid were detected with an automatic analyzer (Hitachi 7080, Hitachi). In addition, Hcy levels were measured via enzyme-linked immunosorbent assay (ELISA). All tests are carried out in accordance with provided instructions.

| MTHFR C677T genotyping
In order to determine whether patients were carriers of the MTHFR C677T polymorphism, whole blood samples collected using EDTA as an anticoagulant were used for genotyping via Taqman probe technology. In the HapMap database, MTHFR is located from positions chr1:11768374 to 11788702, with C677T being located at position rs1801133. ABI (USA) synthesized the Taqman probe that was used for this genotyping experiment, and automated PCR reactions were conducted using a Roche Applied Science LightCycler 480 instrument.

| Patient baseline characteristics
In total, 185 patients of Zhuang nationality with hypertension were enrolled in this study and were divided into two groups based upon whether or not their plasma Hcy level was >15 μmol/L, with patients over this threshold being classified as having H-type hypertension and those below it being classified as having non-H-type hypertension.
The baseline characteristics of patients in both groups are compiled in Table 1. Patient body weight, SBP, DBP, LDL-C, HDL-C, coronary heart disease incidence, diabetes incidence, and cerebral infarction incidence did not differ significantly between groups (P > .05). Relative to the non-H-type group, the frequency of male patients, average age, and average urea nitrogen, creatinine, and uric acid levels were significantly higher among patients with H-type hypertension (P ≤ .05, Table 1).

| Comparison of cardiac ultrasound findings between patient groups
When echocardiographic findings were compared between these two patient groups, we found that there were no significant differences in any of the three measured indicators between patients with H-type and non-H-type hypertension (P > .05; Table 2).

| The relationship between the MTHFR C677T polymorphism and Hcy levels
Lastly, we analyzed the relationship between MTHFR C677T allele frequencies and Hcy levels in this hypertensive patient population (Table 3). In patients with H-type hypertension, MTHFR C677T genotype frequencies for the CC, CT, and TT genotypes were 67.11%, 25%, and 7.89%, respectively, while they were 66.06%, 29.36%, and 4.59% among patients with non-H-type hypertension, respectively, with no significant difference between these groups (χ 2 = 1.14, P = .57). Allele frequencies in the H-type group (C, 40.74%; T, 42.47%) and non-H-type group (C, 59.26%; T, 57.53%) did not differ significantly (χ 2 = 0.072, P = .79). These findings thus indicated that the MTHFR C677T polymorphism was not significantly related to elevated Hcy levels in this Guangxi Zhuang nationality population of hypertensive patients (both P > .05).

| D ISCUSS I ON
Herein, we found that elevated Hcy levels were associated with in-  In this study, we assessed the underlying clinical charac- found that C677T polymorphism was associated with hypertension (OR = 1.36, 95% CI = 1.20-1.53). 11 In addition, a separate study based on a Chinese population also found that the MTHFR C677T gene polymorphism was associated with a higher risk of H-type hypertension. 12 The different study populations in these analyses may Hyperhomocysteinemia is an independent risk factor associated with both cardiovascular disease and stroke incidence. [13][14][15] This condition results from elevated tHcy plasma levels and can impact arterial structure and function, thereby increasing the risk of cardiovascular disease, stroke, pre-eclampsia, and neurological disease. [16][17][18] Many studies have defined a clear link between HHcy and hypertension, and the underlying mechanism is thought to be linked to the disrupted function of vascular endothelial and smooth muscle cells. 19