A factor XI deficiency associated with a nonsense mutation (Trp501stop) in the catalytic domain

We identified a novel mutation in an asymptomatic 65‐year‐old Japanese man with severe factor XI deficiency. Sequence analysis after polymerase chain reaction single‐stranded conformation polymorphism (PCR‐SSCP) analysis of his factor XI gene revealed a G→A transition in codon 501 of exon 13, resulting in a substitution of Trp501 (T G G) by a stop codon (T A G) in the catalytic domain. This mutation abolished a Fok I restriction site. The PCR product from normal subjects was digested with Fok I and yielded two fragments, one of 223 bp and one of 47 bp. The PCR product from the patient gave a single 270‐bp fragment, demonstrating possible homozygosity.