the c957t gene polymorphism is a synonymous mutation located within the 957th base pair of the drd2 gene. this base pair is located in exon 7. most synonymous mutations are silent. however, the c957t mutation is an exception to this rule. while the 957c allele codes for the same polypeptide as the 957t allele, the conformation of 957t messenger rna differs from the conformation of 957c messenger rna. 957t messenger rna is less stable and more prone to degradation. as a result, dopamine d2 receptor expression is decreased among individuals who carry the 957t allele compared to individuals who carry the 957c allele.