Activation-resistant homozygous protein C R229W mutation causing familial perinatal intracranial hemorrhage and delayed onset of thrombosis

- Protein C is a natural anticoagulant and its deficiency increases risk of thrombosis.
- Homozygous protein C gene (PROC) c.811 C > T mutation (R229W) was identified in one family.
- Protein C R229W mutation was linked to perinatal intracranial bleeding and delayed onset of thrombosis.
- Recombinant protein C mutant R229W is resistant to thrombin:thrombomodulin activation.

IntroductionWe describe a family with two first-degree cousins who presented with similar phenotypes characterized by neonatal intracranial hemorrhage and subsequent onset of thrombosis.Patients/methodsWe enrolled the two affected patients, five unaffected family members and fifty-five normal controls. Clinical, laboratory, and radiological characteristics of patients were obtained. Exome sequencing was performed for the older affected child. PROC c.811 C > T was genotyped by PCR in patients, family members, and controls. Protein C amidolytic activity and antigen were measured using the STACHROM® protein C kit and ELISAs. To define functional abnormalities caused by the patients' mutation, recombinant wildtype protein C and its mutants R229W, R229Q and R229A were studied.ResultsFor the two cousins, protein C amidolytic activity was 61% and 59% and antigen was 57% and 73% (nl 70-140%), respectively. Exome sequencing revealed a homozygous variant in exon 9 of the protein C (PROC) gene c.811 C > T (R229W). The R229W mutation is located in the calcium binding loop of protein C's protease domain that mediates thrombomodulin interactions. Recombinant R229W-protein C mutant was strikingly defective in rate of activation by thrombin: thrombomodulin, suggesting an in vivo deficit in these children for generation of activated protein C.ConclusionsThese cases emphasize that protein C and activated protein C are important in maintaining the integrity of the brain vascular endothelium in humans. Moreover, routine protein C assays utilizing snake venom protease fail to detect protein C mutants that are resistant to thrombin:thrombomodulin activation.