Definite diagnosis in Japanese patients with protein C deficiency by identification of causative PROC mutations

Protein C is a vitamin K-dependent plasma glycoprotein that functions as an important regulator of blood coagulation, and its deficiency is known to be a risk factor for thrombosis [1]. Congenital protein C deficiency is an autosomally inherited disorder, and has been classified into 2 types: a quantitative deficiency (type I), and qualitative deficiency (type II) [2]. Heterozygous patients with inherited protein C deficiency are mildly affected, and are either symptomatic (1 in 16,000 of the general population [3]) or asymptomatic (1 in 500 of the healthy population [4]). Thus, protein C deficiency in itself is thought to be a relatively mild risk factor for thromboembolism, and it is suggested that thrombosis-prone protein C deficient families might carry additional genetic factors that increase the risk, such as FV Leiden mutation and prothrombin 20210G [ A mutation in Caucasian populations [5]. Severe congenital protein C deficiency is a much rarer disease, most often caused by a homozygous (or compound heterozygous) protein C gene (PROC) mutation(s). Some homozygous subjects develop purpura fulminans or skin necrosis and intravascular disseminated coagulation at birth [6–8], while heterozygous deficiency predisposes to venous thrombosis in adulthood. This clinical heterogeneity could reflect a variety of molecular mechanisms. The prevalence of protein C deficiency in the general Japanese population was also estimated similarly to be approximately 1 in 500 [9]. In this study, we investigated the molecular defects of protein C deficiency in 6 Japanese patients, and defined respective causative mutations in the PROC. All patients were diagnosed as having protein C deficiency (Table 1) [10]. After informed consents were obtained, genomic DNAs were isolated from peripheral blood leukocytes of the patients and studied under approval of the study from the Ethics Committee of the Nagoya University School of Medicine. We amplified each of the 8 exons including the exon/intron boundaries of the PROC by polymerase chain reaction (PCR), and directly sequenced them as described previously [7]. We identified 6 distinct heterozygous PROC mutations in the 6 Japanese patients with protein C deficiency: 5 missense mutations (p.Arg42Ser [c.124C [ A], p.Met406Ile [c.1218G [ A], p.Cys147Tyr [c.439G [ A], p.Arg211Trp [c.631C [ T], A. Takagi R. Tanaka D. Nakashima Y. Fujimori T. Yamada K. Okumura T. Murate T. Kojima Department of Pathophysiological Laboratory Sciences, Nagoya University Graduate School of Medicine, Nagoya, Japan