Association of MTHFR C677T polymorphism with severity and localization of chronic atrophic gastritis patients without Helicobacter pylori infection: a case control study

Gastric cancer is the third primary cause of cancer-related death in the world [1]. According to the Correa’s theory, a series of precancerous lesions (atrophic gastritis [AG], intestinal metaplasia [IM], and dysplasia) is caused by chronic inflammation of the gastric mucosa, which leads to the evolution of stomach cancer [2]. AG is a chronic disorder losing the oxyntic glands, which is characterized by lamina propria fibrosis or their replacement with pseudo-pyloric or IM [3]. Therefore, early supervision of AG could reduce the incidence of gastric cancer [4].

Cancer development is a result of intricate interactions between genetic and environmental factors. Epigenetic changes like DNA methylation play an important part in cancer development [5]. 5,10-Methylenetetrahydrofolate reductase (MTHFR) has a role in folate metabolism and is associated with DNA, RNA, and protein methylation [6]. MTHFR C677T polymorphism is associated with various tumors, as this change in sequence reduces the activity of this enzyme [6, 7]. Indeed, individuals with the TT and CT genotypes have mildly higher homocysteine levels than CC homozygotes [8]. In addition, hyperhomocysteinemia is a growing risk for different precancerous lesions according to its observed effects on morbidity and mortality among patients [9, 10]. Previous studies have shown that gastric diseases might cause hyperhomocysteinemia through nutrient malabsorption [11]. As a result, AG patients with TT genotype have a much higher risk of gastric cancer. Therefore, MTHFR C677T polymorphism might be useful in predicting the development and severity of gastrointestinal cancer, especially in Asian populations [12‐14]. However, the function of MTHFR C677T polymorphism in stomach precancerous lesions is still unclear. Therefore, based on the risk levels (0-IV) ranked by the Operative Link on Gastritis Assessment (OLGA) and Operative Link on Gastric Intestinal Metaplasia Assessment (OLGIM) grading systems [15], we investigated the relationship between MTHFR C677T polymorphism and AG in Helicobacter pylori-negative patients in this study.

DNA methylation is a pivotal epigenetic modification that can be altered in precancerous lesions [2]. As MTHFR is the key gene and metabolite in the one-carbon metabolism pathway that contributes to the provision of methyl groups and metabolism of homocysteine [22, 23], the MTHFR C677T polymorphism may be considered as a reliable factor for predicting the prognosis of gastric precancerous lesions [24, 25]. The reduced activity of the MTHFR enzyme resulting from TT mutation has been linked to aberrant DNA or RNA synthesis, repair, and chromosomal damage [6]. This study evaluated the degree of atrophy and IM in different biopsies to examine whether the TT genotype confers an increased risk for developing moderate-to-severe lesions (moderate-to-severe atrophy or IM in any one biopsy) in patients without H. pylori infection. In addition, patients with TT genotype were found to be at a higher risk of OLGA and OLGIM stages III-IV compared to patients with the CC + CT genotypes. It has been shown previously that OLGA stages I-II are associated with a lower risk while stages III-IV are associated with a higher risk of gastric cancer [26, 27]. Thus, in our study, the TT genotype was a risk factor for gastric precancerous lesions in patients without H. pylori infection. It is noteworthy to mention that conflicting results have been reported on the influence of the MTHFR C677T polymorphism on precancerous lesions or cancer. Some studies have shown an increased risk of gastric cancer development among Asians and Caucasians [12, 28], while others studies have reported a negative association [29, 30]. Conflicting results indicate that population-specific and geographical factors may account for this phenomenon. For example, the results in our study were based on the study group which included patients who were H. pylori negative. However, the study from Itou et al. was based on the study group which included both H. pylori negative and positive patients and did not examine the influence from the H. pylori infection [31]. In addition, the inconsistent results may be due to the methods of confirming the atrophic gastritis. In previous study, gastric atrophy was only evaluated with serum pepsinogens (PGI < 70 ng/dl and PGI/II < 3) while all pathological diagnoses were made by histological examination of gastric biopsy samples in our study [31]. It is well established that histological examination is still the gold standard. In studies using histological examination, MTHFR C677T genotypes can monitor stomach cancer risk among atrophic gastritis patients [32].

In addition, we should routinely include the incisura biopsies in sampling protocol for patients with TT genotype for further screening of gastric cancer risk. The incisura is the main lesion for the early-onset of atrophic-metaplastic evolution [33]. It may undergo more severe lesions than the antrum or corpus [34, 35].

A cross-sectional study showed an age-related trend with a growing prevalence of AG in people aged 35–44 years compared to those older than 44 years in Sweden [36]. The morbidity age for AG patients without H. pylori infection seems to be younger than previously thought. Previous studies suggested that the growing prevalence of overweight and obese patients resulted in this unexpected trend [36, 37]. In our AG population, we did not find such an association between the severity of AG and overweight or obesity (BMI shown in Table 1, P > 0.05). These observations in our study may be due to the fact that we did not establish a control group in the general population for comparison with AG patients, as was done in the study by Song et al. [36]. However, when we divided patients into two age groups (27–44 years and 45–80 years), the frequency of the TT genotype was much higher in the younger age group than in the older age group, indicating that AG patients with TT genotype might have a younger morbidity age and a longer duration of illness. As a result, AG patients with TT genotype may suffer from more severe gastric diseases. Previous studies have confirmed that aging is an independent risk factor for AG progression to gastric cancer [38]. In general population, the prevalence of AG in persons over 40 years is double that in those under 40 years [39]. In our study, however, the frequency of the TT genotype was lower in patients over 44 years of age. This may be due to some important transition of the dominant mechanism. Further research on the difference in MTHFR C677T genotype frequency in these two AG age groups is warranted.

Folate deficiencies may cause uracil misincorporation during DNA synthesis, which increases cancer risk [40]. The data from our study suggest that AG patients with TT genotype have a higher rate of folate deficiency compared with those with the CC + CT genotypes (P = 0.001), which will theoretically bring a higher rate of hyperhomocysteinemia. However, in our study, this was not the case. No significant difference was observed (P = 0.819), indicating that the AG may be more of a direct cause of hyperhomocysteinemia, which is in good agreement with previous research [11]. This phenomenon suggests that the AG factor may play a more important role in the presence of hyperhomocysteinemia than the MTHFR C677Tgenotype. As a result, AG patients are suggested to receive folic acid supplementation to reduce the risk of gastric cancer.

Although not statistically significant, patients with TT genotype in our study showed a trend towards a higher frequency of more severe lesions according to the Kimura-Takemoto endoscopic classification. In addition, some studies have reported that the severity of gastric atrophy assessed by the Kimura-Takemoto endoscopic classification is correlated with OLGA and OLGIM stages [21, 41]. In our study, however, the correlation was weak with a kappa value of 0.29.

To our knowledge, our study provides the first observation of an association between the MTHFR C677T polymorphism and gastric precancerous lesions in patients without H. pylori infection. We suggest that the TT genotype is associated with more severe lesions in H. pylori -negative patients. The biopsy of the incisura in AG patients with TT genotype will be useful for further screening of gastric cancer risk, especially for patients younger than 44 years. AG itself may be a contributing factor towards hyperhomocysteinemia. In addition, patients should be cautious about the potential risk of cardiovascular diseases in view of the association between hyperhomocysteinemia and vascular injury [42].