Homozygous protein C deficiency with moderately severe clinical symptoms.

We report a large family with two members homozygotes for protein C deficiency, with activity levels of 5% and 9%. Thirteen additional members were heterozygotes, with protein C activity ranging from 36-66% and equally low levels of protein C antigen. The homozygotes presented with recurrent deep-vein thromboses and pulmonary emboli, but have reached the ages of 26 and 37 years. Hence, protein C levels of 5% appear sufficient to avoid life-threatening clinical symptoms in the neonatal period.