Prevalence of FACTOR IX-R338L (FACTOR IX PADUA) IN A COHORT of PATIENTS with Venous Thromboembolism and Mild Elevation of FACTOR IX LEVELS.

Elevated plasma levels of blood coagulation factor IX (FIX) have been associated with increased risk of venous thromboembolism (VTE) in humans. However, the molecular mechanisms underlying elevated FIX have not been elucidated. Recently, a mutation in the FIX gene resulting in a FIX molecule with Arginine Leucine substitution at position 338 (FIX-R338L or Factor IX Padua) has been associated with very high levels of FIX (776%) in a patient with spontaneous VTE. Recombinant expression of FIX-R338L confirmed the gain-of-function mutation.

Here we evaluated the levels of FIX and the prevalence of Factor IX Padua in a cohort of patients with VTE followed at our center. The prevalence of FIX Padua was evaluated by using a PCR-RFLP strategy by which PCR with specific primers was followed by digestion with the enzyme TaqI.

The prevalence of FIX Padua was evaluated in a population of 192 patients with spontaneous VTE (69 males and 123 females; median age 36-yo). A population of 192 healthy individuals matched for age, sex and ethnicity was used as a control group for the determination of FIX levels. Median FIX levels was 128.0% (61.0-207.0%) in patients with VTE. Twenty-nine patients presented FIX levels above the 90th percentile (160.2%). Factor IX Padua was not identified in any patients or controls, even in those with elevated FIX levels.

in the present study FIX Padua was not identified in any of our patients, indicating that this mutation is not associated with mild elevations of FIX levels frequently observed in patients with VTE.

No relevant conflicts of interest to declare.