Venous Thrombotic Risk in Family Members of Unselected Individuals with Factor V Leiden
R. P. M. Lensen (1) , R. M. Bertina (2) , H. de Ronde (2) , J. P. Vandenbroucke (1) , F. R. Rosendaal (1),(2)
From the (1) Department of Clinical Epidemiology, Leiden University Medical Center, (2) Hemostasis and Thrombosis Research Center, Department of Haematology, Leiden University Medical Center, The Netherlands
The factor V Leiden mutation (FVL) leads to a seven-fold increased
risk of venous thromboembolism (VTE). In thrombophilic families,
25% of carriers have experienced thrombosis before the age of
40 years. Aim of our study was to assess the association of FVL with
VTE in first-degree family members of unselected symptomatic and
asymptomatic carriers of FVL.
We tested 197 relatives of consecutive thrombosis patients with
FVL and 36 relatives of asymptomatic carriers on the presence of FVL
and the occurrence of VTE.
The incidence of VTE in relatives with FVL of symptomatic carriers
was 0.34%/year. This was similar to the incidence in relatives with
FVL of asymptomatic carriers. Kaplan Meier analysis in relatives of
symptomatic propositi showed that at the age of 58 years, thrombosisfree
survival was reduced to 75% in carriers and 93% in non-carriers
(P < 0.05). Carriers of FVL had a three times higher thrombotic risk
than non-carriers. In combination with environmental risk factors, FVL
clearly adds to the risk of VTE. The thrombotic incidence rate in these
unselected relatives with FVL, however, is considerably lower than was
seen in carriers of thrombophilic families (1.7%/year). Therefore,
special care should be paid to individuals with a positive family history
of venous thrombosis while exposed to these risk factors.