What is the pathophysiology of type I protein C deficiency?

Updated: Jan 04, 2019
  • Author: Shamudheen Rafiyath, MD; Chief Editor: Perumal Thiagarajan, MD  more...
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Type I protein C deficiency refers to a quantitative deficiency in the plasma protein C concentration. Heterozygous individuals typically demonstrate protein C antigen and activity levels that are approximately one half that of normal patient plasma. A range of causative genetic alterations within the protein C promoter region and splice sites as well as in the coding sequence of the protein C gene itself have been reported. [7]

There is marked phenotypic variation among families with heterozygous type I protein C deficiency. Some families exhibit a severe thrombotic tendency, whereas others remain asymptomatic. [8, 9, 10] Interestingly, this variability is seen even among different pedigrees that harbor the same protein C mutation, suggesting that the mutation itself does not fully explain the phenotypic variability. [11] The presence of a second thrombophilic mutation such as factor V Leiden has been associated with a more severe phenotype in some protein C–deficient kindreds. [12]

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