Rapid detection of a protein C gene mutation present in the asymptomatic and not in the thrombosis‐prone lineage

The presence of mutations in the serine protease domain of protein C was investigated by temperature gradient gel electrophoresis of PCR products in five patients with protein C deficiency and thrombosis. Molecules with an altered melting behaviour were detected in one subject with a history of venous and arterial thrombosis. Direct sequencing showed that a G deletion, present in the heterozygous state, caused a reading frame shift at Trp 300 and subsequently a premature termination at the codon 335. The resulting suppression of the protein C catalytic function explains the reduction of protease activity to half. In addition the mutation caused a reduction of the antigen level in plasma. Temperature gradient gel electrophoresis enabled the rapid detection of the gene alteration in the family of the propositus. Several members of the paternal lineage had had severe thrombotic episodes. Unexpectedly the mutation was found to be inherited from the clinically asymptomatic maternal lineage, thus suggesting that an additional unknown defect from the paternal lineage is present in the thrombosis-prone propositus.