Paris I dysfibrinogenemia: a point mutation in intron 8 results in insertion of a 15 amino acid sequence in the fibrinogen gamma-chain.

Paris I dysfibrinogenemia results in the production of a fibrinogen molecule containing a functionally abnormal gamma-chain. We determined the basis of the molecular defect using polymerase chain reaction (PCR) to amplify the gamma-chain region of the Paris I subject's genomic DNA. Comparative sequence analysis of cloned PCR segments of normal and Paris I genomic DNA revealed only an A-->G point mutation occurring at nucleotide position 6588 within intron 8 of the Paris I gamma-chain gene. We examined six normal individuals and found only normal sequence in this region, indicating that this change is not likely to represent a normal polymorphism. This nucleotide change leads to a 45 bp fragment being inserted between exons 8 and 9 in the mature gamma Paris I chain mRNA, and encodes a 15 amino acid insert after gamma 350 [M-C-G-E-A-L-P-M-L-K-D-P-C-Y]. Alternative splicing of this region from intron 8 into the mature Paris I gamma-chain mRNA also results after translation into a substitution of S for G at position gamma 351. Biochemical studies of 14C-iodoacetamide incorporation into disulfide-reduced Paris I and normal fibrinogen corroborated the molecular biologic predictions that two additional cysteine residues exist within the gamma Paris I chain. We conclude that the insertion of this amino acid sequence leads to a conformationally-altered, and dysfunctional gamma-chain in Paris I fibrinogen.