Compound heterozygosity for two novel mutations in a severe factor XI deficiency.

We identified two novel mutations in an asymptomatic 25-year-old Japanese patient with severe factor XI deficiency. Direct sequencing analysis of PCR products from his factor XI gene revealed a G to T transversion in exon 12, resulting in the nonsense mutation (Glu447Stop) and a G insertion in five consecutive guanine nucleotides ((501)Trp(TGG)-(502)Gly(GGG)) in exon 13 that is expected to lead to the substitution of the last 105 amino acids ((503)Tyr-(607)Val) with 32 abnormal amino acid residues ((503)Val-(534)Thr) followed by stop codon. We also demonstrated that two mutations are associated with the separate alleles in this patient, indicating compound heterozygosity for these mutations. Both mutations lead to the disruption of the catalytic domain structure of the FXI molecule and thus are responsible for his deficiency of factor XI. Copyright 2003 Wiley-Liss, Inc.