Two common, functional polymorphisms in the promoter region of the beta-fibrinogen gene contribute to regulation of plasma fibrinogen concentration

Plasma fibrinogen is a major risk factor for coronary heart disease, stroke , and peripheral artery disease. There is evidence that genetic variation i n the beta-fibrinogen gene contributes to the rate of synthesis of fibrinog en, but the molecular mechanism underlying the genetic heritability of the plasma fibrinogen concentration is largely unknown. We evaluated the physio logical roles of 5 common nucleotide substitutions in the promoter region o f the beta-fibrinogen gene at positions -148, -249, -455, -854, and -993 fr om the transcriptional start site. Electrophoretic mobility shift assays re vealed distinct differences in the binding characteristics of nuclear prote ins between wild-type and mutant fragments of both the -455G/A and -854G/A polymorphisms, whereas no clear differences were observed for the -148C/T, -249C/T, and -993C/T sites. Transfection studies in HepG2 cells showed incr eased basal rates of transcription for both the G-to-A substitution at posi tion -455 (+50%, P<0.05) and the G-to-A substitution at -854 (+51%, P<0.05) . Additional transfection studies using proximal promoter constructs confir med that both the -455A and -854A alleles independently enhance the basal r ate of transcription of the beta-fibrinogen gene. The rare alleles of the n onrelated -455G/A and -854G/A polymorphisms were also associated with signi ficantly increased plasma fibrinogen levels in healthy middle-aged men. Ove rall, the 2 polymorphisms together explained approximate to 11% of the vari ation in plasma fibrinogen concentration. It is concluded that the -455G/A and -854G/A polymorphisms of the beta-fibrinogen gene are physiologically r elevant mutations with a significant impact on the plasma fibrinogen concen tration.