Abstract
We identified a novel mutation in an asymptomatic 72-year old Japanese woman with severe factor XI (FXI) deficiency. Sequence analysis showed a homozygous missense mutation Trp599Arg (g.234T-->C according to Genbank accession number
M20218). This residue belongs to a region conserved in human FXI and the FXI of several animals. Molecular modeling showed that the Trp599 residue is positioned in an alpha helix in the C-terminal region of the FXI molecule.