Eaton Allison M, Sandler Robert, Carethers John M, Millikan Robert C, Galanko Joseph, Keku Temitope O
Department of Epidemiology, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7555, USA.
Cancer Epidemiol Biomarkers Prev. 2005 Aug;14(8):2023-9. doi: 10.1158/1055-9965.EPI-05-0131.
The 5,10-methylenetetrahydrofolate reductase (MTHFR) gene plays a critical role in folate metabolism. Studies on the association between MTHFR polymorphisms and length changes in short tandem repeat DNA sequences [microsatellite instability (MSI)] are inconsistent. Using data from colon cancer cases (n=503) enrolled as part of an existing population-based case-control study, we investigated the association between MTHFR 677 and MTHFR 1298 polymorphisms and MSI. We also examined whether the association was modified by folate intake. Participants were case subjects enrolled as part of the North Carolina Colon Cancer Study. Consenting cases provided information about lifestyle and diet during in-home interviews as well as blood specimens and permission to obtain tumor blocks. DNA from normal and tumor tissue sections was used to determine microsatellite status (MSI). Tumors were classified as MSI if two or more microsatellite markers (BAT25, BAT26, D5S346, D2S123, and D17S250) had changes in the number of DNA sequence repeats compared with matched nontumor tissue. Tumors with one positive marker (MSI-low) or no positive markers (microsatellite stable) were grouped together as non-MSI tumors (microsatellite stable). MTHFR 677 and MTHFR 1298 genotypes were determined by real-time PCR using the 5' exonuclease (Taqman) assay. Logistic regression was used to calculate odds ratio (OR) and 95% confidence intervals (95% CI). MSI was more common in proximal tumors (OR, 3.8; 95% CI, 1.7-8.4) and in current smokers (OR, 4.0; 95% CI, 1.6-9.7). Compared with MTHFR 677 CC referent, MTHFR 677 CT/TT genotype was inversely associated with MSI among White cases (OR, 0.36; 95% CI, 0.16-0.81) but not significant among African Americans. Although not statistically significant, a similar inverse association was observed between MTHFR 677 CT/TT genotype and MSI among the entire case subjects (OR, 0.54; 95% CI, 0.26-1.10). Among those with adequate folate intake (>400 microg total folate), we found strong inverse associations between combined MTHFR genotypes and MSI (677 CC+1298 AC/CC, OR, 0.09; 95% CI, 0.01-0.59; 677 CT/TT+1298 AA, OR, 0.13; 95% CI, 0.02-0.85) compared with the combined wild-type genotypes (677 CC+1298 AA). This protective effect was not evident among those with low folate (<400 microg total folate) intake. Our results suggest that MTHFR variant genotypes are associated with reduced risk of MSI tumors under conditions of adequate folate intake, although the data are imprecise due to small numbers. These results indicate that the relationship between MTHFR genotypes and MSI is influenced by folate status.
5,10-亚甲基四氢叶酸还原酶（MTHFR）基因在叶酸代谢中起关键作用。关于MTHFR基因多态性与短串联重复DNA序列长度变化[微卫星不稳定性（MSI）]之间关联的研究结果并不一致。利用作为现有基于人群的病例对照研究一部分纳入的结肠癌病例（n = 503）的数据，我们调查了MTHFR 677和MTHFR 1298基因多态性与MSI之间的关联。我们还研究了这种关联是否会因叶酸摄入量而改变。参与者是作为北卡罗来纳州结肠癌研究一部分纳入的病例受试者。同意参与的病例在家庭访谈中提供了有关生活方式和饮食的信息，以及血液样本并允许获取肿瘤组织块。来自正常和肿瘤组织切片的DNA用于确定微卫星状态（MSI）。如果与匹配的非肿瘤组织相比，两个或更多微卫星标记（BAT25、BAT26、D5S346、D2S123和D17S250）的DNA序列重复数发生变化，则肿瘤被分类为MSI。具有一个阳性标记（低MSI）或无阳性标记（微卫星稳定）的肿瘤被归为非MSI肿瘤（微卫星稳定）。MTHFR 677和MTHFR 1298基因型通过使用5'核酸外切酶（Taqman）测定法的实时PCR确定。采用逻辑回归计算比值比（OR）和95%置信区间（95%CI）。MSI在近端肿瘤（OR，3.8；95%CI，1.7 - 8.4）和当前吸烟者中更常见（OR，4.0；95%CI，1.6 - 9.7）。与MTHFR 677 CC参照组相比，MTHFR 677 CT/TT基因型在白人病例中与MSI呈负相关（OR，0.36；95%CI，0.16 - 0.81），但在非裔美国人中不显著。尽管无统计学意义，但在整个病例受试者中，MTHFR 677 CT/TT基因型与MSI之间也观察到类似的负相关（OR，0.54；95%CI，0.26 - 1.10）。在叶酸摄入量充足（总叶酸>400微克）的人群中，我们发现与联合野生型基因型（677 CC + 1298 AA）相比，联合MTHFR基因型与MSI之间存在强负相关（677 CC + 1298 AC/CC，OR，0.09；95%CI，0.01 - 0.59；677 CT/TT + 1298 AA，OR，0.13；95%CI，0.02 - 0.85）。在叶酸摄入量低（总叶酸<400微克）的人群中，这种保护作用不明显。我们的结果表明，在叶酸摄入量充足的情况下，MTHFR变异基因型与MSI肿瘤风险降低相关，尽管由于样本量小数据不太精确。这些结果表明MTHFR基因型与MSI之间的关系受叶酸状态影响。
