Haplotype structure of the fibrinogen gene cluster. (A) Haplotypes and typed htSNPs of the fibrinogen gene cluster. Numbering is according to Seattle-SNPs.⁸  The numbering of the haplotypes in the 3 genes is arbitrary. (B) Alternative mRNA processing of γ chain mRNA. The γA chain is translated from mRNA in which all 9 introns of the pre-mRNA were removed and polyadenylation occurred downstream of exon 10 at polyadenylation site 2 (pA2). In contrast, the γ′ chain arises from alternative processing of the FGG pre-mRNA. Intron 9 is not removed, and polyadenylation occurs at an alternative site located in this intron at polyadenylation site 1 (pA1). This leads to the translation of a polypeptide with a unique 20-amino acid extension encoded by intron 9 substituted for the carboxyl terminal 4 amino acids of the γ chain encoded by exon 10.^21,22  This variant chain comprises approximately 7% to 15% of the fibrinogen γ chain found in plasma.¹⁰  Nearly all the γ′ protein occurs in vivo as a heterodimer with the γA variant in which one D region contains a γ′ carboxyl terminus and the other a γA carboxyl terminus (γA/γ′ fibrinogen).²³  SNPs 9615C>T and 10034C>T are specific for haplotype 2 of FGG.