We report a missense mutation of protein C (PC) gene in a family with type II congenital. PC deficiency. The proband was a 17-year-old high school student with deep venous thrombosis and pulmonary embolism. Hemostatic examinations revealed normal amidolytic activity and PC antigen level measured by a chromogenic snake venom assay and an EIA utilizing a polyclonal antibody, respectively. However, anticoagulant activity measured by the activated partial thromboplastin time method and immunological antigen level estimated by a monoclonal antibody recognizing the Ca2+-dependent conformational change were reduced. Two other members. of this family (father and paternal grand-mother) showed the identical defect, but they had been asymptomatic. The functional abnormalities were most likely to be due to alternation in the Gla domain. Subsequently, a polymerase chain reaction (PCR) strategy and an allele-specific oligonucleotide (ASO) hybridization were used to evaluate exon 3 of the PC gene. Sequence analysis following amplification of exon 3 and its flanking regions showed a single G to A transition, resulting in the conversion of Glu26 codon (GAG) to Lys26 codon (AAG). Since this missense mutation generated no new restriction site, the PCR-amplified exon 3 fragments from this family member were hybridized with ASOs corresponding to the normal and mutated sequences. An identical mutation was detected in the affected family members of the proband by the ASO hybridization. These data indicate that conversion of the Glu26 codon (GAG) to Lys26 codon (AAG) was responsible for the type II congenital PC deficiency inherited in this Japanese family.
