Polymorphisms of Folate Pathway Enzymes (Methylenetetrahydrofolate Reductase and Thymidylate Synthase) and Their Relationship with Thymidylate Synthase Expression in Human Astrocytic Tumors

Two important polymorphisms of folate cycle enzymes, methylenetetrahydrofolate reductase (MTHFR) C677T and thymidylate synthase (TS) enhancer region (TSER) 28-bp tandem repeat, are related to risk of various types of cancer, including brain tumors, although there are few studies on this subject. A case-control study of these two polymorphisms in astrocytomas of different grades was carried out using polymerase chain reaction-restriction fragment length polymorphism, also determining the immunohistochemical expression of TS. The MTHFR 677 TT genotype was less associated with astrocytic tumors (odds ratio [OR] = 0.00; p = 0.0238), but the TSER polymorphism did not show any significant association. Combined genotype TT-double repeats/triple repeats (2R/3R) had a protective effect against astrocytomas (OR = 0.00; p = 0.0388). Expression of TS protein was observed in the majority of cases, with grade IV tumors being the exception. Moreover, the median H-score for the pilocytic astrocytomas was significantly higher when compared with that for diffuse tumors. There was an inverse correlation between the 2R/2R genotype and the highest TS-expressing tumors, and 3R/3R was relatively more frequent among the tumors grouped in the third and fourth quartiles. Our results provide support for the role of MTHFR and TS polymorphism in gliomagenesis, possibly because of the alteration of DNA methylation and repair status. Moreover, high levels of TS expression were detected in these tumors.