Risk of thrombosis in patients homozygous and heterozygous for factor V Leiden in the East Bohemian region.

A retrospective investigation on the frequency of thrombotic events in 227 heterozygous and 16 homozygous carriers for the factor V R506Q mutation (factor V Leiden) from 102 unrelated families in the East Bohemian region is reported. A majority of 130 of the 227 (57%) heterozygous and a minority of 5 of 16 (31%) homozygous carriers for the factor V R506Q mutation remained asymptomatic. Deep venous thrombosis without pulmonary embolism in a minority was the main and the most frequent clinical manifestation in 97 of 243 carriers for the factor V R506Q mutation. Deep venous thrombosis occurred in 92 of 227 (41%) heterozygous and in 11 of 16 (69%) homozygous carriers of the factor V R506Q. Spontaneous thrombosis prevailed in symptomatic men. Thrombosis in women usually occurs during risk situations well known to elicit venous thrombosis. Oral contraceptives and pregnancy were significantly the most frequent risk factors in female carriers of the factor V R506Q mutation, which in fact can readily explain the lower average age for the first thrombotic event of 30.6 years in women compared to 37.1 years in men.