Objective: To study the prevalence of Activated Protein C (APC) resistance due to Factor V Leiden (FV Leiden) mutation among the first generation immigrants from India and Pakistan with venous thromboembolism (VTE).
Introduction: APC resistance due to the substitution of Arginine 506 by Glutamine in coagulation Factor V is caused by G1691A mutation in exon 10 of Factor V gene. This is the commonest cause of inherited thrombophilia in Caucasians, but the frequency of this mutation is low in non-Caucasians. Among subjects in the Physician Health Study, the frequency of FV Leiden was found to be 5.27% in Caucasian Americans vs. 0.45% in Asian Americans. Another study found no mutation in 191 Asian Americans tested. In non-Caucasians with VTE, it is generally considered not cost effective to screen for this mutation. However Asians are a heterogeneous group and the Leiden gene frequency varies among different ethnic populations. While the frequency of FV Leiden gene has been documented to be low in China, Korea, Japan, Thailand, Indonesia etc, the frequency in India and Pakistan is not well studied. Two studies found a carrier frequency of 2% (Rees et al) and 4.2 % (Gou et al) among the general population from India and Pakistan. This is similar to the frequency found in Middle Eastern and European population. We did not come across any study of FV Leiden gene frequency in patients with VTE from India and Pakistan.
Patients and Methods: A retrospective chart review of patients of Indian or Pakistani origin seen at Coney Island Hospital, from July 1996 to June 2003, who had a work up for inherited thrombophilia after an episode of VTE. During the chart review age, sex, first or recurrent episode and any predisposing factors such as immobilization, malignancy, hormonal therapy, surgery, pregnancy, and the presence of SLE or MPD were noted. Thrombophilia work up included functional assays for Protein C, S and Antithrombin III, Lupus anticoagulant, ACA and Homocysteine levels. APC resistance was measured by a clotting assay using Factor V depleted plasma and all patients who were borderline or resistant were tested for the presence of FV Leiden mutation by PCR.
Results: A total of 18 patients were studied. All had an episode of VTE documented by a Doppler ultrasonography or a Ventilation Perfusion lung scan or a CT angiogram. 3 out of 18 patients (16.6%) had APC resistance. All the three patients were confirmed to be heterozygous for FV Leiden mutation. Two were male and one was a female with a median age of 36 yrs (27, 36 and 57 yrs). The female patient had a recurrent episode, first one occurred during pregnancy, but the second episode had no precipitating events. One male patient had trauma to the leg and was immobilized at the time of the VTE, another male patient was a cab driver by occupation. None of the patients had any other concurrent inherited thrombophilic state.
Conclusions: The prevalence of the FV Leiden mutation is significantly high among South Asians with VTE in our study. If the findings are confirmed by a larger study, screening for this mutation for thrombophilia would be relevant in patients of South Asian origin and screening recommendations for family members would be identical to Caucasian population. The high prevalance as in Caucasians suggests a founder effect and possible spread of the mutation by the migration of Neolithic farmers from the Middle East towards Europe and India, ten thousand years ago. This has been confirmed by haplotype analysis.