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Mutations and common polymorphisms in ADAMTS13 gene responsible for von Willebrand factor-cleaving protease activity
Koichi Kokame1, Masanori Matsumoto, Kenji Soejima
1Research Institute, National Cardiovascular Center, Suita, Osaka 565-8565, Japan.
Abstract:
von Willebrand factor (VWF) is synthesized primarily in vascular endothelial cells and secreted into the plasma as unusually large VWF multimers. Normally, these multimers are quickly degraded into smaller forms by a plasma metalloproteinase, VWF-cleaving protease (VWF-CP). Decreases in the activity of this enzyme result in congenital and acquired thrombotic thrombocytopenic purpura (TTP). The human VWF-CP has recently been purified. Cloning of the corresponding cDNA revealed that the 1,427-aa polypeptide is a member of the ADAMTS gene family, termed ADAMTS13. Twelve rare mutations in this gene have been identified in patients with congenital TTP. Here, we report missense and nonsense mutations in two Japanese families with Upshaw-Schulman syndrome, congenital TTP with neonatal onset and frequent relapses. The comparison of individual ADAMTS13 genotypes and plasma VWF-CP activities indicated that the R268P, Q449stop, and C508Y mutations abrogated activity of the enzyme, whereas the P475S mutant retained low but significant activity. The effects of these mutations were further confirmed by expression analysis in HeLa cells. Recombinant VWF-CP containing either the R268P or C508Y mutations was not secreted from cells. In contrast, Q449stop and P475S mutants were normally secreted but demonstrated minimal activity. Genotype analysis of 364 Japanese subjects revealed that P475S is heterozygous in 9.6% of individuals, suggesting that approximately 10% of the Japanese population possesses reduced VWF-CP activity. We report on a single-nucleotide polymorphism associated with alterations in VWF-CP activity; it will be important to assess this single-nucleotide polymorphism as a risk factor for thrombotic disorders.
Insights
Mutations in the ADAMTS13 gene cause Upshaw-Schulman syndrome, a form of thrombotic thrombocytopenic purpura (TTP). Certain mutations reduce VWF-cleaving protease (VWF-CP) activity, impacting VWF multimer degradation and potentially increasing thrombotic risk.
Area of Science:
- Genetics
- Hematology
- Molecular Biology
Background:
- Von Willebrand factor (VWF) is crucial for hemostasis, normally regulated by VWF-cleaving protease (VWF-CP).
- Deficiency or dysfunction of VWF-CP leads to thrombotic thrombocytopenic purpura (TTP), a serious bleeding and clotting disorder.
- The human VWF-CP is encoded by the ADAMTS13 gene, with known mutations causing congenital TTP.
Purpose of the Study:
- To investigate novel mutations in the ADAMTS13 gene in Japanese families with congenital TTP (Upshaw-Schulman syndrome).
- To characterize the functional impact of identified ADAMTS13 mutations on VWF-CP activity and secretion.
- To assess the prevalence of a specific ADAMTS13 single nucleotide polymorphism (SNP) in the Japanese population and its potential association with altered VWF-CP activity.
Main Methods:
- Genetic analysis of patients with congenital TTP to identify mutations in the ADAMTS13 gene.
- Functional assays using recombinant VWF-CP expressed in HeLa cells to evaluate the activity and secretion of mutant proteins.
- Genotyping of a large Japanese cohort to determine the frequency of a specific ADAMTS13 SNP.
Main Results:
- Identified missense and nonsense mutations (R268P, Q449stop, C508Y, P475S) in ADAMTS13 in two Japanese families with congenital TTP.
- Mutations R268P and C508Y abrogated VWF-CP secretion, while Q449stop and P475S mutants were secreted but showed minimal activity.
- The P475S mutation was found in 9.6% of the 364 Japanese subjects, suggesting approximately 10% of the population may have reduced VWF-CP activity.
Conclusions:
- Specific ADAMTS13 mutations identified in Japanese families lead to severe VWF-CP deficiency and congenital TTP.
- The P475S mutation is a common variant in the Japanese population, potentially contributing to reduced VWF-CP activity.
- Further investigation of this ADAMTS13 SNP as a risk factor for thrombotic disorders is warranted.