Two Novel Mutations (G774A and A1685G) Causing Coagulation Factor XII Deficiency in a Patient with Acute Inferior...

To identify the gene mutation of the coagulation factor XII (FXII) in a patient with FXII deficiency and acute inferior myocardial infarction.

The proband was a 51-year-old Chinese man who was diagnosed with acute inferior myocardial infarction and had a history of FXII deficiency. The patient presented with a prolonged activated partial thromboplastin time (160 s) and decreased FXII activity (2.3%) and FXII antigen (1%). DNA sequence analysis of the FXII gene was performed by next generation sequencing. The mutant FXII cDNAs were constructed in an expression plasmid vector and transfected into 293T cells. The expression of FXII antigen was detected by western blot.

Sequencing of the FXII gene revealed two novel heterozygous mutations, one at exon 8 (G774A; p: W258X) and the other at exon 14 (A1685G; p: D562G). Western blot showed that the FXII antigens were detected only in the supernatant and whole cell lysate of the wild-type and A1685G mutant type, but not in G774A or G774A plus the A1685G mutant type. In addition, the results showed that secretion but not synthesis of A1685G mutant protein was markedly reduced compared to the wild type.

The present study indicated that the G774A mutation might impair the secretion and synthesis of FXII protein, while the A1685G mutation only influences the secretion of FXII protein. The definition of these new mutations could be useful tools for analyzing the intracellular protein transport and structure-function relationship of FXII protein transport in the future.