A common genetic polymorphism (46 C to T substitution) in the 5'-untranslated region of the coagulation factor XII gene is associated with low translation efficiency and decrease in plasma factor XII level

We studied the Hga I polymorphism (46 C/T) in the 5'-untranslated region of the coagulation factor XII (FXII) gene corresponding to four bases upstream from the ATG translation initiation codon. By using allele-specific restriction analysis with restriction endonuclease Hga I, the allele frequency of 46C/T was estimated to be 0.27/0.73 in Orientals (allele number =152), and conversely, 0.8/0.2 in Caucasians (allele number =40). Because it has been reported that plasma levels of FXII were lower in Orientals than in Caucasians, we investigated the relationship between this polymorphism and plasma levels of FXII. As a result, there were significant differences in plasma FXII levels between these three allele types: C/C,170+/-38% (178+/-27%); C/T, 141+/-29% (123+/-34%); and T/T, 82+/-19% (61+/-11%) [FXII activity (FXII antigen levels)]. In heterozygotes of 46 C/T both alleles were equally transcribed in hepatocytes, as determined by reverse transcription polymerase chain reaction (RT-PCR), suggesting little influence of the polymorphism at the level of transcription or on the stability of mRNA. In in vitro transcription/translation analysis, less FXII was produced from cDNA containing 46 T than from that containing 46 C. Therefore, it is highly likely that the 46 T polymorphism in the FXII gene decreased the translation efficiency and led to low plasma levels of FXII activity and antigen, probably due to the creation of another ATG codon and/or impairment of the consensus sequence for the translation initiation scanning model.