A novel gene insertion combined with a missense mutation causing factor VII deficiency in two unrelated Chinese families

A novel homozygous missense mutation (Met527Ile) in a consanguineous marriage family with inherited factor XII deficiency

OBJECTIVE

To identify potential mutations of the FXII gene (F12) in a consanguineous marriage family with hereditary coagulation factor XII (FXII) deficiency, and it will improve the understanding of the pathogenesis involved in the disease.

CLINICAL PRESENTATION

The proband was a 58-year-old male who had chronic gastritis. He was found to have a significantly prolonged activated partial thromboplastin time (APTT) at 101.0s (reference range, 29.0-43.0 s) before stomachendoscopy.

TECHNIQUES

The coagulation factor XII activity (FXII:C) and FXII antigen (FXII:Ag) were measured by one-stage clotting assay and enzyme-linked immunosorbent assay, respectively. The F12 gene was amplified by polymerase chain reaction and sequenced. Mutation sites were further confirmed by reverse sequencing. The conservatism and possible impact of the amino acid substitution were analyzed by multiple bioinformatics tools, as well as 3D protein model analysis.

RESULTS

The proband had a prolonged APTT (101.0 s), whose FXII:C and FXII:Ag were obviously reduced, both at 1.0% (normal range, 72-113%). Gene sequencing revealed that he carried a homozygous missense mutation of Met527Ile. Family study showed that his mother, son and daughter carried a heterozygous Met527Ile. Bioinformatics and model analysis of the mutation indicated that Met527Ile may be detrimental and potentially alters the structure and the function of the protein.

CONCLUSION

The novel mutation Met527Ile could potentially account for the reduced activity of FXII in this family.