SEARCH FOR MUTATIONS IN THE GENES FOR COAGULATION-FACTOR-V AND COAGULATION-FACTOR-VIII WITH A POSSIBLE PREDISPOSITION TO ACTIVATED PROTEIN-C RESISTANCE

A total of 74 non-pregnant women with a previous episode of thrombosis were investigated for activated protein C (APC) resistance in the aPT T-based and factor Ma-X-based assays and for the presence of mutations in all APC-cleavage sites in the heavy chains of factor V and factor VIII. DNA fragments were amplified with the polymerase chain reaction (PCR) and those encoding for the Arg-306 and Arg-506 (factor V) and fo r Arg-740 (factor VIII) cleavage sites were subjected to restriction e nzyme analysis. DNA fragments of 29 selected patients corresponding to the Arg-306 and Arg-679 cleavage sites in factor V, and to the Arg-33 6 and Arg-562 cleavage sites in factor Vm were sequenced. APC resistan ce was found in 40 cases, using the aPTT-based assay and in 35, using the factor Ma-X-based assay (23 patients were APC resistant in both as says), whereas 22 individuals had a normal response to APC. Forty-thre e patients carried Arg-506 to Gin mutation in factor V. No other polym orphism or mutation was found in the genes for factors V or Vm in the vicinity of the APC cleavage sites. It was concluded that the differen ce in response to APC in the two assays may not be explained by the pr esence of mutations in the APC cleavage sites of factor V and factor V m in this group of patients. The data do not exclude the presence of m utations elsewhere in the factor V or factor VIII genes.