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Previous Volume 361:1671-1675 October 22, 2009 Number 17 Next

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SUMMARY

We report a case of juvenile thrombophilia associated with a substitution of leucine for arginine at position 338 (R338L) in the factor IX gene (factor IX–R338L). The level of the mutant factor IX protein in plasma was normal, but the clotting activity of factor IX from the proband was approximately eight times the normal level. In vitro, recombinant factor IX–R338L had a specific activity that was 5 to 10 times as high as that in the recombinant wild-type factor IX. The R338 substitution causes a gain-of-function mutation, resulting in factor IX that is hyperfunctional.

Source Information

From the Department of Cardiologic, Thoracic and Vascular Sciences, 2nd Chair of Internal Medicine, University of Padua Medical School, Padua, Italy (P.S., D.T., G.T., S.G., C.B., L.S., C.R.); and the Department of Pediatrics, Children's Hospital of Philadelphia (N.P.I., J.D.F., V.R.A.), and the University of Pennsylvania School of Medicine (V.R.A.) — both in Philadelphia.

Address reprint requests to Dr. Simioni at the Department of Cardiologic, Thoracic and Vascular Sciences, 2nd Chair of Internal Medicine, Via Giustiniani 2, 35100 Padua, Italy, or at paolo.simioni{at}unipd.it.

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