Low risk of thrombosis in family members of patients with hyperhomocysteinaemia.

Mild to moderate hyperhomocysteinaemia, a metabolic disorder due to genetic and/or acquired factors, is associated with an increased risk of venous and arterial thrombosis. To establish whether measuring homocysteine in members of families of hyperhomocysteinaemic patients is warranted, we investigated 169 relatives of patients diagnosed with hyperhomocysteinaemia after they developed arterial or venous thrombosis. The prevalence of hyperhomocysteinaemia was 16.6%; the relative risk of thrombosis in relatives with hyperhomocysteinaemia compared to those without was 1.2 (odds ratio; 95% CI 0.24-4.2), with similarly low absolute annual incidences of thrombosis (0.28% and 0.24%). The low prevalence of hyperhomocysteinaemia among relatives of patients with this metabolic disorder, and their low risk of thrombosis, do not justify family screening.