Severe factor XI deficiency caused by compound heterozygosity for the type III mutation and a novel insertion in exon 9 (codons 324/325+G)

We investigated a 42-year-old Caucasian woman with severe factor XI deficiency and her family members. Restriction enzyme analysis and DNA sequencing revealed compound heterozygosity in the patient for the known type III mutation, which is a Phe283Leu amino acid substitution in the fourth apple domain causing impaired dimerization and secretion, and for a novel frameshift mutation in exon 9 (codons 324/325 +G), leading to premature termination with lack of parts of the fourth apple domain and the downstream serine protease domain.