Protein C deficiency.

Protein C deficiency is a rare genetic trait that predisposes to thrombotic disease. It was first described in 1981. The disease belongs to a group of genetic disorders know as thrombophilias.
The prevalence of protein C deficiency has been estimated to about 0,2% of the general population.

Protein C deficiency is associated with an increased incidence of venous thromboembolism (relative risk 7), whereas no association with arterial thrombotic disease has been found.(more...)

Other sites

http://omim.org/entry/176860

http://medinfo.ufl.edu/year2/coag/cdef.html

http://www.nlm.nih.gov/medlineplus/ency/article/000559.htm

http://www.uptodate.com/contents/protein-c-deficiency?source=search_result&search=Protein+C+Deficiency&selectedTitle=1~53

http://www.medterms.com/script/main/art.asp?articlekey=5082