Characterization of antithrombin variants in thrombotic patients with normal and reduced activity.
R. Deshpande1, B. Kulkarni1, K. Ghosh2, S. Shetty1 (1Mumbai, India, 2Surat, India)
Time: 17:15 - 18:15
Objective: To characterize mutations in AT deficient and normal patient with arterial and venous thrombosis and correlate mutations with the laboratory and clinical phenotype. To analyse the feasibility of the most suitable technique for an accurate diagnosis of AT deficiency.
Methods: Patients with Arterial and venous thrombosis having low AT activity were screened for the presence of mutations in SERPINC1 gene by direct DNA sequencing. 500 (arterial 125; venous 375) patients with normal AT levels were screened for the presence of mutations in exon 5. AT activity was measured by chromogenic assay based on thrombin (IIa) and Xa inhibition. AT antigen was measured by ELISA and rocket immunoelectrophoresis. 100 normal healthy controls randomly selected to match with the cases by age; sex and geographical area and were sequenced for exon 5. Also 50 patients with borderline AT activity were sequenced for all seven exon and promoter region of SERPINC1 gene.
Results: 2 patients presented with heterozygous type I mutation, p.Ala126Asp and p.Arg164stop; 1 patient presented with type II mutation, a rare case with homozygous p.Met121Val. In Patients with normal AT activity, P305H mutation was seen to be more common and is present in much conserved region on AT gene. 10 out 11 patients with this mutation suffered from cerebral thrombosis and 1 patient had splenic infarct. H351P mutation was found to be deleterious by two of the three prediction softwares. 1 borderline patient presented with splice site variant in promoter region.
Conclusion: In this study, 2 type I and 1 type II mutations are detected. Type I is the most severe type of all AT mutations. Also 4 variants with normal AT activity of which mutations P305H and H351P were found to be deleterious in prediction softwares. Recent evidences show that some SERPINC1 mutations responsible for functional abnormality of AT often show slightly decreased or even normal activity and cannot be detected by currently available laboratory assays. The data strongly suggests that genetic screening for variants in SERPINC1 gene should be performed in all thrombosis cases. Also, genetic counseling and screening of family members is important to prevent further thrombotic episodes.