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Molecular characterization of coagulation factor XII deficiency in a Japanese family
Hideo Wada1, Junji Nishioka, Yasunari Kasai
1Department of Laboratory Medicine, Mie University School of Medicine, Tsu, Mie, Japan. wadahide@clin.medic.mie-u.ac.jp
Abstract:
We report the identification in a Japanese family of a novel homozygous W486C mutation in the protease domain of coagulation factor XII (FXII), which was associated with the reduction of plasma FXII activity and antigen level to less than 5% of normal. Sequences of each exon for FXII gene was analysed in family members by polymerase chain reaction (PCR) amplification followed by a direct sequencing method. Sequence analysis showed a homozygous substitution of G to C at nucleotide position 10587 (cDNA position 1458) in proband's FXII gene, resulting in a Trp to Cys substitution in the catalytic domain of FXII. PCR-fragment length polymorphism analysis of 55 healthy volunteers showed no such mutation. Transient expression of FXII in HK-293T cells and analysis of FXII antigen in culture media and cell lysates showed reduced secretion of mutant protein by more than 84% relative to that of wild type protein although the intracellular contents were similar. Our results suggest that the reduced secretion of FXII protein was due to incorrect folding caused by the introduction of Cys486. We designated this mutation as FXII Mie-1.
Insights
Researchers identified a new mutation in the coagulation factor XII (FXII) gene in a Japanese family, leading to significantly reduced FXII activity and levels. This finding sheds light on FXII deficiency causes.
Area of Science:
- Genetics
- Hematology
- Molecular Biology
Background:
- Coagulation Factor XII (FXII) plays a crucial role in the intrinsic pathway of blood coagulation.
- FXII deficiency is a rare bleeding disorder, often asymptomatic, but can be associated with thrombosis or bleeding in some cases.
- Understanding the genetic basis of FXII deficiency is important for diagnosing and managing related hemostatic disorders.
Observation:
- A novel homozygous W486C mutation was identified in the protease domain of the FXII gene in a Japanese family.
- Proband's plasma FXII activity and antigen levels were reduced to less than 5% of normal.
- Sequence analysis revealed a specific G to C substitution (c.10587G>C) leading to a Tryptophan to Cysteine substitution (p.Trp486Cys) in the catalytic domain.
Findings:
- The identified W486C mutation was absent in 55 healthy volunteers, indicating it is a rare genetic variant.
- Transient expression studies showed that the mutant FXII protein was secreted at a rate over 84% lower than the wild-type protein.
- Intracellular levels of the mutant FXII protein were comparable to the wild-type, suggesting a defect in protein secretion rather than synthesis.
Implications:
- The W486C mutation likely causes FXII deficiency by inducing incorrect protein folding, leading to impaired secretion of FXII.
- This study identifies a specific genetic cause (FXII Mie-1) for severe FXII deficiency, contributing to the understanding of FXII's role in hemostasis.
- Further research may explore the clinical phenotype associated with this specific mutation and its impact on coagulation and thrombosis risk.