G691S, L769L and S836S ret proto-oncogene polymorphisms are not associated with higher risk to sporadic medullary thyroid carcinoma in Chilean patients

Medullary thyroid carcinoma (MTC) may occur either as sporadic or as hereditary. Even though the sporadic form corresponds to the majority of cases, the pathogenesis is still unclear. Several polymorphisms of the ret proto-oncogene, including those located in exon 11, 13, 14 and 15 have been described in the general population and some of them seem to be over-represented in sporadic MTC patients from European countries, especially G691S, L769L and S836S. To evaluate the allele frequencies of these variants in Chilean patients and controls and to determine if these polymorphisms would be associated with the development of sporadic MTC from a different genetic population base. Fifty sporadic MTC patients and 50 normal subjects were tested for G691S, L769L, S836S and S904S polymorphisms. The extracted genomic DNA was initially analyzed by direct sequencing of PCR products in patients. The presence or absence of each polymorphism was also assessed in patients and in control by restriction digestion. The allele frequencies showed a similar level of the G691S, L769L and S904S variants in both groups. Of interest, we found an under-representation of S836S polymorphism in the sporadic MTC group but this number was not statistically significant (p=0.141). We did not find an over representation of the G691S, L769 and S836S. These results argue against the validity of the association of these polymorphisms as contributing factors in the development of sporadic MTC based on a Chilean population and raise questions about the importance of these polymorphisms overall.