Study group characteristics and distribution of MTHFR (C677T, A1298C) and MTRR (A66G) polymorphisms
Characteristics of the patients and controls are shown in Table 1. The HGB, vitamin B12, and plasma folate levels and the RBC count were significantly lower in patients than in controls (P<0.05). Conversely, the MCV and Hcy in patients were obviously higher than those in controls (P<0.01). However, the distribution of other clinical characteristics such as gender and age between patients and controls did not show significant differences (P>0.05).
The distribution of MTHFR (C677T, A1298C) and MTRR (A66G) alleles and genotypes in patients and controls did not deviate from the Hardy-Weinberg equilibrium. As shown in Table 2, TT genotype frequency of MTHFR (C677T) was higher in patients (31.7%) than in controls (10.0%, P<0.01), which was the susceptive genotype for MA occurrence (OR = 0.171, 95% CI = 0.044–0.667). The T allele of MTHFR (C677T) was more frequent in patients (53.7%) than in healthy subjects (32.5%, P<0.01) and it was closely related to MA (OR = 0.416, 95% CI = 0.220–0.787). Moreover, no statistically significant difference was observed in the distribution of the other genotypes, including CT (C677T), AC/CC (A1298C), and AG/GG (A66G) genotypes, between patients and controls (P>0.05). The distribution of C (A1298C) and G (A66G) alleles was not significantly different between patients and controls (P>0.05). However, in combined genotypes, which were grouped into wild type (CC+AA+AA), heterozygous mutation type (CC/CT+AA/AC+AA/AG), and homozygous mutation type (Table 2), the distribution of these three genotype groups showed significant differences between patients and controls (P<0.05). In addition, the proportion of homozygous mutations in patients was significantly higher and that of heterozygous mutations in patients was significantly lower than those in the normal controls (P<0.05). The frequencies of wild type, heterozygous type, and homozygous type in MA patients were 2.4% (1/41), 46.3% (19/41), and 51.2% (21/41), whereas those in controls were 7.5% (3/40), 70.0% (28/40), and 22.5% (9/40), respectively.
Comparison between clinical examination indices of MA and genotypes
The relationship between clinical features of MA, including vitamin B12, folic acid, MCV, RBC, HGB, and Hcy, and the MTHFR or MTRR genotypes are shown in Table 3. TT genotypes had lower vitamin B12 level, HGB level and RBC count than 677CC and 677CT genotypes of MTHFR (C677T) (P<0.05). In MTRR (A66G) mutations, patients with AG genotypes showed lower vitamin B12 and higher MCV levels than those with AA genotypes (P<0.05). Meanwhile, subjects with 66GG genotypes showed a higher MCV level than those with 66AA genotypes (P<0.05). However, no significant differences in folic acid levels were detected among 677CC, 677CT, and 677TT genotypes of MTHFR (C677T) (P>0.05). Furthermore, there were no significant differences among the above six clinical examination indices in MTHFR (A1298C) (P> 0.05).
Comparison of clinical examination indices of MA with polymorphism scoring system
The risk of MA was evaluated according to the clinical examination indices including MCV, vitamin B12, folic acid, Hcy, and HGB levels and RBC count. The data displayed that the scores were positively correlated with MCV and Hcy concentrations, but negatively correlated with HGB, folic acid, and vitamin B12 concentrations and RBC count (Fig. 1, P<0.05).
Then the cases were divided into two groups according to the scores—low-risk group and high-risk group. Higher MCV and Hcy levels (Table 4, P<0.05) and lower HGB, RBC, folic acid, and vitamin B12 levels were noted in the high-risk group than in the low-risk group (Table 4, P<0.05). Moreover, the high-risk group displayed a higher prevalence rate of MA than that did the low-risk group (36.6% vs 15.0%, Table 4, P<0.05).