Possible Impact of RET Polymorphism and Its Haplotypic Association Modulates the Susceptibility to Thyroid Cancer

Rearranged during Transfection (RET) gene polymorphisms act to influence thyroid cancer in a polygenic and low-penetrance manner and no study regarding RET alterations in thyroid cancer has undergone from this part of the world (North India). We evaluated RET G691S (rs1799939), L769L (rs1800861), and S904S (rs1800863) polymorphisms to elucidate their possible role as risk factors in papillary thyroid cancer (PTC) and follicular thyroid cancer (FTC). Polymorphic analysis of RET gene was performed by polymerase chain reaction (PCR), followed by restriction fragment length polymorphism (RFLP). In RET G691S polymorphism, the overall distribution of variant alleles (GA + AA) in cases was 62.9% as against 44.5% in controls (P < 0.05) whereas frequency of RET L769L variant alleles (TG + GG) in cases was 70% versus 88% in controls (P < 0.05). In RET S904S, frequency of variant alleles (CG + GG) in cases was 56% versus 44% in controls (P < 0.05). Interestingly, G691S/L769L variant showed increased risk for the non-smokers (P < 0.05). RET S904S variant showed association with benign thyroid disease as against those with no history. The over-representation of homozygotes in G691S and L769L polymorphic variants was not observed, which suggest a "Dominant mode of inheritance." The S904S polymorphism heterozygote lies almost in the middle of the two homozygotes confirming an "Additive mode of inheritance." In conclusion, RET gene G691S/S904S polymorphisms were over-represented and L769L polymorphism was under-represented in PTC and FTC patients. RET polymorphic variants could act synergistically in the development or progression of PTC and FTC.