Hereditary protein C deficiency caused by compound heterozygous mutants in two independent Chinese families

We report two compound heterozygous mutants that caused severe type I protein C (PC) deficiency in two independent Chinese families.PC antigen was determined by enzyme-linked immunosorbent assay (ELISA), and PC activity was measured by chromogenic assay. Genetic mutations were screened with polymerase chain reaction (PCR) followed by direct sequencing. PC mutants were transiently expressed in COS-7 cells for the evaluation of PC secretory activity and function. The subcellular location was visualised by immunofluorescence assay. The structural analysis of mutation was performed as well.Compound heterozygous mutations of Arg178Trp and Asp255His with reduced PC activity and antigen levels were identified in Proband 1, a 28-year-old male with deep vein thrombosis (DVT) and pulmonary embolism. The other mutations of Leu-34Pro and Thr295Ile with reduced PC activity and antigen levels were identified in Proband 2, a 19-year-old male with DVT. The PC activities with Arg178Trp, Asp255His, Leu-34Pro and Thr295Ile mutations decreased significantly. Immunofluorescence assay demonstrated that only trace amount of PC with novel Thr295Ile mutation was transported to the Golgi apparatus. Subsequent structural analysis indicated severe impairments of intracellular folding and secretion.The two rare compound heterozygous mutations could cause type I PC deficiency via impairment of secretory activity of PC.