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Polymorphisms in clotting factors
By Sharon Guynup

Some polymorphisms of genes that affect blood-clotting factors may lower the risk of brain hemorrhage, according to a Spanish research team.

Changes in certain elements of the hemostatic system, such as platelets and coagulation factors, can trigger bleeding or create life-threatening blood clots. Javier Corral and colleagues at the Hospital General Universitario in Murcia, Spain, sought to characterize genetic alterations that could increase or decrease the risk of intracranial bleeding.

The Spanish team studied genomic DNA from blood samples of 201 patients who had suffered an episode of intracranial hemorrhage and compared it to the DNA obtained from 201 controls. Using genomic polymerase chain reaction (PCR), they genotyped four polymorphisms: factor V Leiden (FV Leiden), prothrombin 20210A, factor VII (-323) deletion/insertion of 10 nucleotides, and factor XIII V34L. Each of these polymorphisms affects clotting factors and influences levels and/or the function of proteins that alter the coagulation response.

The team made two important discoveries. Carriers of FV Leiden had "almost a 5-fold decreased risk for intracranial hemorrhage than those lacking the genetic variant." This is the first report to characterize FV Leiden in a protective role in acquired bleeding disorders.

Moreover, the researchers found that carriers of the FVII -323 Ins allele, which is associated with lower levels of FVII in plasma, had an increased risk for brain hemorrhage. "This genetic change could be involved in the etiology of this disease," the researchers concluded. A larger study group will be needed to confirm these findings.

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Corral, J. et al. Polymorphisms of clotting factors modify the risk for primary intracranial hemorrhage. Blood 97, 2979-2982 (May 15, 2001).

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