Demographic characteristics, allelic frequencies, and CDKN2A methylation status
The characteristics and allele frequencies observed among the UC patients enrolled in this study are shown in Table 2. The allele distribution of MIF (rs755622) met the criteria for HWE (p = 1.00). We found no differences with respect to mean age, gender, clinical type, or extent of disease among those with methylated and unmethylated p14ARF or p16INK4a. The minor allele frequency of rs755622 was somewhat higher in the group with p14ARF methylation; of note, the frequency of the C allele carrier was significantly higher (p = 0.01). By contrast, no significant differences in the minor allele frequencies associated with rs755622 were observed when comparing the p16INK4a methylated and unmethylated groups. Similarly, the 7-repeat allele frequency of rs5844572 was significantly higher in the p16INK4a methylated group compared to unmethylated group (p=0.036), but no significant differences were observed when comparing the p14ARF methylated and unmethylated groups.
Association between MIF polymorphisms and methylation status of p14ARF or p16INK4a
The frequency of p14ARF methylation was significantly higher among subjects with the rs755622 C allele; a similar trend was observed after adjusting for confounding factors including age, gender, clinical type, and extent of disease. These results indicate that the presence of the rs755622 C allele was a significant risk factor associated with p14ARF methylation (Table 3; OR, 2.16; 95% CI, 1.08–4.32). By contrast, no significant relationship was found between p16INK4a methylation and the allele frequencies associated with rs755622.
We previously revealed that 7 CATT repeat allele of rs5844572 promotes inflammation. Thus, we assessed the influence of the 7-repeat allele. The 7-repeat allele of the rs5844572 polymorphism of p16INK4a was detected at higher frequency among those in the methylated group compared to any of the other alleles; this trend was even more prominent after adjustment for the aforementioned confounding factors. As such, our findings indicate that carrying the rs5844572 7-repeat allele was a significant risk factor for p16INK4a methylation (Table 4; OR, 2.57; 95% CI, 1.26–5.24). By contrast, there were no significant relationships between p14ARF methylation and rs5844572 allele frequencies.
Demographic characteristics and allele frequencies of subjects demonstrating no methylation or methylation of both p14ARF and p16INK4a
Comparisons among groups demonstrating methylation of both p14ARF and p16INK4a with those in which both were unmethylated are shown in Table 5. The allele distribution of MIF (rs755622) in both methylated and neither methylated groups met the criteria for HWE (p=0.73 and p=0.72, respectively). There were no significant differences with respect to clinicopathological backgrounds between these two groups.
The minor allele frequencies associated with rs755622 were significantly higher in the group in which both p14ARF and p16INK4a were methylated compared to the fully unmethylated group (p=0.029); the C allele carrier was detected at significantly higher frequency (p=0.020). Similarly, the frequency of the rs5844572 7-repeat allele was significantly higher in the group in which both p14ARF and p16INK4a were methylated compared to the fully unmethylated group (p=0.0090).
Association between MIF polymorphisms and CDKN2A methylation
The results of an analysis in which confounding factors were adjusted revealed that carrying the rs755622 C allele and the rs5844572 7-repeat allele was significantly associated with an increased methylation of both p14ARF and p16INK4a (OR, 2.70; 95% CI, 1.22–6.01 and OR, 2.87; 95% CI, 1.25–6.62, respectively; Table 6).
Association between MIF polymorphisms and CDKN2A methylation in phenotype of UC
Next, we investigated in what kind of UC phenotype the significant association of MIF polymorphisms with CIHM of CDKN2A was seen (Table 7). Carrying rs755622 C allele was significantly associated with CIHM chronic continuous of clinical type and total colitis (OR, 25.9; 95% CI, 2.55-262.6 and OR, 4.38; 95% CI, 1.12-17.2, respectively). Meanwhile, carrying 7 repeat allele of rs5844572 was significantly associated in chronic continuous type (OR, 14.5; 95%CI, 1.46-144.3).