Summary
We describe a previously unreported defect of protein S characterized by low levels
of cofactor activity for activated protein C contrasting with low normal levels of
total and free protein S antigen. The distribution of protein S between the free form
and the form complexed with the complement component C4b-binding protein was normal
on two-dimensional immunoelectrophoresis. The proband developed juvenile deep-vein
thrombosis while taking oral contraceptives. Her defect was transmitted in an autosomal
dominant fashion from her asymptomatic mother. Other relatives carrying the same laboratory
abnormality (mother, maternal uncle, two sisters and one brother) were also asymptomatic.
We postulate that the defect is due to a dysfunctional protein S present in plasma
in normal amounts and with normal proportions of the free and complexed forms of the
protein.
Keywords
Protein S - Protein C - Inherited thrombosis - Deep-vein thrombosis
