Congenital Factor XI deficiency in an elderly Japanese male accompanied by nonsense mutation p.Trp519* and novel missense mutation p.Ile618Phe.

OBJECTIVE

In the present study, we identified a genetic mutation in a patient with asymptomatic congenital Factor XI (FXI) deficiency, with an FXI activity of <1%. The mutation was accidentally discovered when the patient was 80 years old.

METHODS

We performed genome sequencing (GS) on using a whole blood sample from the patient. The nucleotide sequences obtained were compared to the FXI reference GS and mutations were assessed using BioEdit.

RESULTS

Notably, exon 14 was not amplified;therefore, all other exons were analyzed. Four heterozygous nucleotide mutations were noted:c.1556G>A, c.1812G>T, c.1839G>A, and c.1852A>T;c.1556G>A and c.1852A>T were associated with amino acid substitutions p.Trp519* and p. Ile618Phe, respectively. Some cases of the amino acid substitution p.Trp519* have been registered in the database;however, to the best of our knowledge, p.Ile618Phe was likely discovered for the first time in this study.

CONCLUSION

Because both gene mutations were heterozygous, the patient had compound heterozygous mutations that decreased FXI activity. J. Med. Invest. 73 : 281-285, February, 2026.