Coagulation factor XII deficiency is a rare autosomal recessive disorder, which could be found in a consanguineous family. We studied a Chinese family in which the activated partial thromboplastin time (APTT) of the proband had clearly prolonged up to 101.7 s, associated with low FXII activity of 3% and FXII antigen < 1%. To analyze the gene mutation in this FXII-deficient patient, we performed FXII mutation screening, and analyzed the DNA sequence of the F12 gene. A ClustalX-2.1-win and four online bioinformatics software services were used to study the conservatism and effects of the mutation. A transient in vitro expression study was performed to elucidate the possible pathological mechanism. Sequence analysis revealed a homozygous c.1681 G > A point mutation in exon 14, causing a novel Gly542Ser mutation in the catalytic domain. The results of the conservatism and bioinformatics analyses both indicated that the mutation likely affects the function of the protein. Additional expression studies in COS-7 cells showed that the antigen level of mutant FXII (FXII-Gly542Ser) was lower than wild type in culture medium, whereas the corresponding level of FXII antigen in cell lysates was equivalent. These results suggest that the Gly542Ser mutation causes FXII deficiency through intracellular degradation.

No abstract

: The objective is to study a gene mutation (Tyr503Cys) found in a Chinese consanguineous marriage family with inherited factor XI (FXI) deficiency (cross-reacting material positive, type II). The FXI activity and FXI antigen were tested with clotting assay and ELISA, respectively. The FXI gene was amplified by PCR with direct sequencing. ClustalX-2.1-win and three online bioinformatics softwares were used to study the conservatism and harm of the mutation. The proband had reduced FXI: activity at 13%; three members had decreased to about 35%, all of whom had nomal FXI: antigen. DNA sequencing analysis showed the proband carried a homozygous c.1562A>G point mutation of F11, resulting in Tyr503Cys. Tyr503 was highly conserved among the homologous species. The three bioinformatics softwares indicated that the mutation had affected the function of the protein. The Tyr503Cys mutation was responsible for the decrease of FXI: activity, which is cross-reacting material positive deficiency and the first reported in the world.

This was the first report of such a mutation in the position which was associated with dysprothrombinemia.

No abstract