What are the phenotypes of protein S deficiency?

Updated: Jan 03, 2021
  • Author: Mohammad Muhsin Chisti, MD, FACP; Chief Editor: Perumal Thiagarajan, MD  more...
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Based on the measurement of free and total protein S antigen and functional protein S activity, scientists classify protein S deficiency into the following three phenotypes, using the classification proposed at the 1991 meeting of the Scientific Subcommittee of the International Society on Thrombosis and Haemostasis in Munich, Germany:

  • Type I deficiency is characterized by a decrease in the total protein S antigen and free protein S antigen together (quantitative deficiency)

  • Type II deficiency is characterized by normal total and free antigen levels but reduced protein S activity (functional deficiency, qualitative defect)

  • Type III deficiency is characterized by low free protein S levels, whereas the total plasma concentration of protein S is normal

Type II deficiencies are rare. The most common types are I and III. The distinction between type I and type III has no clinical implications, as free protein S levels are reduced in both.

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