NEW YORK (Reuters Health) – The risk for venous thromboembolism (VTE) is significantly higher for those whose sibling also had VTE, researchers from Sweden report in the August 8th online issue of Circulation.

“Until all genetic risk factors are elucidated, family history remains an important risk factor for venous thromboembolism at least between the ages of 10 to 69 years,” Dr. Bengt Zöller from Lund University, Malmö, Sweden told Reuters Health in an email.

VTE affects about 1 in 1000 individuals annually, and heritability of VTE has been estimated to be around 50% to 60%. Little research, however, has addressed the association of family history and risk of VTE or the influence of age and sex on the heritability of VTE.

Dr. Zöller and colleagues used the Swedish Multigeneration Register to analyze the familial risks of hospitalization for VTE among siblings according to age and gender. Total follow-up included 130,659,134 person-years for individuals without a sibling history of VTE and 1,563,505 person-years for individuals with a sibling history of VTE.

There was an increased risk of VTE among siblings that was similar for males (2.52-fold increase) and females (2.37-fold increase).

Between ages 10 and 69 years, the risk of VTE among siblings was higher than the risk among nonsiblings in all age intervals. The increased risk was greatest among siblings aged 10 to 19 years (4.77-fold) and decreased with age to just over 2-fold at age 60 to 69 years.

The risk increase was substantially higher when 2 siblings were affected (51.87-fold) or when at least 3 siblings were affected (53.69-fold) than when only 1 sibling was affected (2.45-fold).

“I was surprised of the high familial risks when two or more siblings were affected,” Dr. Zöller said. “This suggests strong genetic risks factors segregating in these families.”

“It was also interesting that familial non-genetic factors (spouse effect) was so limited, indicating mainly genetic factors contributing to the increased familial risk,” Dr. Zöller noted. “Moreover, we also saw higher risk for thrombosis in younger women than men (especially for those with family history of VTE), while the risk was higher for men compared to women at older age.”

“Half of the thrombotic events are usually provoked by circumstantial factors, such as estrogen containing oral contraceptives, pregnancy, surgery, trauma, and immobilization,” Dr. Zöller added. “Moreover, overweight, smoking, and inactivity might be avoided. Thus, there are possibilities for prevention and prophylaxis in risk situations.”

Age- and Gender-Specific Familial Risks for Venous Thromboembolism
Circulation 8 August 2011.