A Graves' disease-associated Kozak sequence single-nucleotide polymorphism enhances the efficiency of CD40 gene translation:: A case for translational pathophysiology

We analyzed the mechanism by which a Graves' disease-associated C/T polymorphism in the Kozak sequence of CD40 affects CD40 expression. CD40 expression levels on B cells in individuals with CT and TT genotypes were decreased by 13.3 and 39.4%, respectively, compared with the levels in CC genotypes ( P = 0.012). Similarly, Rat-2 fibroblasts transfected with T-allele cDNA expressed 32.2% less CD40 compared with their C-allele-transfected counterparts ( P = 0.004). Additionally, an in vitro transcription/translation system showed that the T-allele makes 15.5% less CD40 than the C-allele ( P< 0.001), demonstrating that the effect of the single-nucleotide polymorphism ( SNP) on CD40 expression is at the level of translation. However, the SNP did not affect transcription, because the mRNA levels of CD40, as measured by quantitative RTPCR, were independent of genotype. Therefore, our results may suggest that the C allele of the CD40 Kozak SNP, which is associated with Graves' disease, could predispose to disease by increasing the efficiency of translation of CD40 mRNA.