PB0559 - Novel Variants of PROS1 Gene Related to Protein S Deficiency

Background: Plasma Protein S (PS) exists in a free and bound form. We discovered that free PS functions as an anticoagulant by directly inhibiting Factor IXa, thereby limiting thrombin generation. Protein S deficiency increases the risks of life-threatening venous thromboembolism and disseminated intravascular coagulation. Protein S deficiency is usually an inherited autosomal dominant condition with variable penetrance. Here, we report a novel PS gene variant in two unrelated individuals who have children with PS deficiency. This variant may create a donor splice site, causing intron retention and altering PS structure and function.

Aims: To assess genetic and protein data related to Protein S deficiency.

Methods: Plasma assays: activated partial thromboplastin time (aPTT), thrombin generation assay (TGA) with addition of PS, immunoblotting, and enzyme linked immunosorbent assays (ELISA). The PROS1 gene was sequenced from whole blood of two control samples and the test samples.

Results: For individual 1, immunoblotting revealed an 18% decrease in total PS, and ELISA revealed a 46% decrease in free PS. The second individual was diagnosed with 49% PS (free) deficiency via ELISA. Functional tests (aPTT and TGA) showed decreased clotting time and increased thrombin generation, which indicated that the individuals had reduced levels of PS. There were five variations in individual 1’s PROS1 gene. Three changes were intron indels that could affect PROS1 splicing. Variant c.1061+62_1061+63 insA in intron 10 was found in both individuals. This insertion may create a donor site according to SSF, MaxEnt and NNSPLICE predictors. Donor site alteration may cause skipping of exon 10 and partial intron retention, a possibility that needs experimental confirmation.

Conclusion(s): Both individuals had reduced levels of PS and the same novel variant in intron 10 of PROS1. Future research should examine the individual’s family histories and assess family members for genetic variations in PROS1.