Three dominant‐negative mutations in factor XI‐deficient patients

Summary. Factor XI (FXI) deficiency results from genetic defects of the F11 gene and is generally considered to be inherited in an autosomal recessive manner. However, the homodimeric structure of FXI allows, in some cases, the dominant‐negative transmission of the disease. The aim of this study was to characterize novel missense mutations in three unrelated patients and verify the dominant‐negative effects of these mutations on the secretion of wild‐type FXI protein by expression studies. The F11 gene was PCR amplified, from genomic DNA extracted from peripheral blood, and sequenced on an ABI 3100 Genetic Analyzer. Human wild‐type FXI and FXI mutants were expressed in BHK570 cells using Lipofectamin transfection reagents. Conditioned media and cell lysates were collected for the measurement of luciferase activity, FXI antigen and Western blot analysis. DNA sequencing revealed three novel missense F11 mutations; c.127G>A in exon 3 (Ala43Thr), c.723C>G in exon 7 (Phe241Leu) and c.1207G>A in exon 11 (Val403Met). In vitro expression studies showed that the mutation Ala43Thr, Phe241Leu or Val403Met remarkably decreased the extracellular secretion of mutant FXI, rather than reducing synthesis of the mutant proteins. Cotransfection of wild‐type FXI with mutant FXI constructs indicated that the mutation Ala43Thr, Phe241Leu or Val403Met reduced the secretion of wild‐type FXI by 75.9%, 68.6% or 71.4%, respectively. Our study suggests that dominant‐negative mutations in FXI‐deficient patients of non‐Ashkenazi Jewish origin may be more prevalent than thought, resulting from FXI’s unique dimeric structure.