Thrombosis in a patient with combined homozygosity for the factor V Leidenmutation and a mutation in the 3 '-untranslated region of the prothrombin gene

The factor V Leiden mutation and a guanine-to-adenine mutation at nucleotid e 20210 in the 3'-untranslated region of the prothrombin gene are the most prevalent genetic defects in patients with deep venous thrombosis. Heterozy gosity for the factor V Leiden and the prothrombin gene mutations is found in approximately 20 and 6% of unselected patients with deep venous thrombos is, respectively, whereas the prevalences of the two mutations in the gener al Caucasian population are approximately 6 and 2%, respectively. We evalua ted an 18-year-old man presenting with a spontaneous episode of superficial venous thrombosis for the presence of an inherited thrombotic disorder. Af ter excluding deficiencies of antithrombin, protein C, and protein S, genom ic DNA from the patient was tested for the presence of the factor V Leiden and prothrombin gene mutations. Consanguinity was not present in the family . Genotyping demonstrated that the patient was homozygous for the factor V Leiden and prothrombin gene mutations. The likelihood of identifying an ind ividual in the general population who is homozygous for both mutations simi lar to our patient is estimated to be less than 1 in 10 million. (C) 1999 L ippincote Williams & Wilkins.