A case-report of two patients with hereditary protein S deficiency treated by rivaroxaban.

: Hereditary protein S deficiency is an autosomal dominant disorder associated with a high risk of venous thromboembolism (VTE) and usually results from mutations of PROS1. Historically heparin and warfarin have been applied as recommended treatment of VTE. Recent researches showed that rivaroxaban provided more consistent and predictable anticoagulation than warfarin. However, it is unknown whether rivaroxaban is effective for the treatment of VTE in patients with thrombophilia, including protein S deficiency, due to lack of evidence. Here, we report two cases of recurrent VTE in two patients with hereditary protein S deficiency, owing to the same nonsense mutation in PROS1, which were successfully treated by rivaroxaban monotherapy.

New functional assays to selectively quantify the activated protein C- and tissue factor pathway inhibitor-cofactor activities of protein S in plasma.

Essentials Protein S is a cofactor of activated protein C (APC) and tissue factor pathway inhibitor (TFPI). There are no assays to quantify separate APC and TFPI cofactor activities of protein S in plasma. We developed assays to measure the APC- and TFPI-cofactor activities of protein S in plasma. The assays were sensitive to protein S deficiency, and not affected by the Factor V Leiden mutation. SUMMARY: Background Protein S plays an important role in the down-regulation of coagulation as cofactor for activated protein C (APC) and tissue factor pathway inhibitor (TFPI). Aim To develop functional assays to quantify the APC- and TFPI-cofactor activities of protein S in plasma. Methods APC- and TFPI-cofactor activities of protein S in plasma were measured using calibrated automated thrombography in protein S-depleted plasma supplemented with a small amount of sample plasma either in the presence of anti-TFPI antibodies and APC (APC-cofactor activity) or at excess full-length TFPI without APC (TFPI-cofactor activity). Total and free protein S levels in plasma were measured by ELISAs. Results Average APC-cofactor activities of protein S were 113%, 108% and 89% in plasma from normal individuals (n = 15), FV Leiden heterozygotes (n = 14) and FV Leiden homozygotes (n = 7), respectively, whereas the average APC-cofactor activity of protein S in plasma from heterozygous protein S-deficient individuals (n = 21) was significantly lower (55%). Similar trends were observed for the TFPI-cofactor activity of protein S, with averages of 109%, 115% and 124% in plasma from individuals with normal protein S levels and different FV Leiden genotypes, and 64% in plasma from protein S-deficient patients. APC-cofactor activities of protein S correlated significantly with free and total protein S antigen levels, whereas TFPI-cofactor activities correlated less with protein S antigen levels. Conclusion We have developed functional protein S assays that measure both the APC- and TFPI-cofactor activities of protein S in plasma, which are hardly if at all affected by the FV Leiden mutation.

Thrombin generation and other coagulation parameters in a patient with homozygous congenital protein S deficiency on treatment with rivaroxaban.

Rivaroxaban, which targets factor Xa and does not reduce proteins C/S, was chosen to treat a 6-year-old girl with homozygous protein S (PS) deficiency who developed skin necrosis while on warfarin. Owing to the lack of experience with rivaroxaban in children, the girl was started with 5 mg once-daily, which was gradually increased to 40 mg daily. The increasing dosage was driven by the need to avoid recurrence of skin necrosis. During dose-escalation, four pharmacokinetics assays were carried out measuring drug plasma concentrations and their effect on hemostatic parameters. We report the laboratory work-up, with special reference to parameters of thrombin-generation. Rivaroxaban concentrations by HPLC were correlated with those by the anti-factor Xa assay (r(2) = 0.92, p < 0.01), but there was an overestimation by HPLC. Thrombin-generation parameters, such as the area under the curve (referred to as ETP), peak-thrombin, and velocity-index, when measured after addition of thrombomodulin, showed unexpected changes: ETP decreased, but peak-thrombin and velocity-index increased. Similar patterns were obtained in a PS-depleted plasma and in plasma from patients with heterozygous PS deficiency, but not in plasma from controls. In conclusion, these preliminary results suggest that PS may be a determinant of velocity and peak-thrombin, but not of the total amount of thrombin generated.

One novel and one recurrent mutation in the PROS1 gene cause type I protein S deficiency in patients with pulmonary embolism associated with deep vein thrombosis.

We investigated the molecular basis of type I protein S (PS) deficiency in two unrelated Japanese families, in which both probands developed pulmonary embolism associated with deep vein thrombosis. Nucleotide sequencing of amplified DNA revealed distinct point mutations in the PROS1 gene of the probands, which were designated protein S Sapporo 1 and protein S Sapporo 2. Additional mutations in the PROS1 gene were excluded by DNA sequencing of all exons and intron/exon boundaries. In the 25-year-old Japanese male patient who carried protein S Sapporo 1, we identified a heterozygous A-to-T change in the invariant ag dinucleotide of the acceptor splice site of intron f of the PROS1 gene. This mutation is a novel splice site mutation that impairs normal mRNA splicing, leading to exon 7 skipping, which was confirmed by platelet mRNA analysis. Translation of this mutant transcript would result in a truncated protein that lacks the entire epidermal growth factor-like domain 3 of the PS molecule. In a 31-year-old Japanese male and his younger brother who each carried protein S Sapporo 2, we detected a previously described heterozygous T-to-C transition at nucleotide position 1147 in exon 10 of the PROS1 gene, which predicts an amino acid substitution of tryptophan by arginine at residue 342 in the laminin G1 domain of the PS molecule. Both mutations would cause misfolding of the PS protein, resulting in the impairment of secretion, which is consistent with the type I PS deficiency phenotype.

Characterization of endoplasmic reticulum-associated degradation of a protein S mutant identified in a family of quantitative protein S deficiency.

INTRODUCTION: Misfolded and unassembled glycoproteins are eliminated from the endoplasmic reticulum (ER) lumen by the ER-associated degradation (ERAD). We previously identified a Tyr595Cys (Y595C) mutation of protein S (PS) in a family of a quantitative PS deficiency. The mutation causes intracellular degradation and decreased secretion of the Y595C mutant PS. The aim of the present study was to further characterize the molecular basis of the intracellular degradation of the mutant. MATERIALS AND METHODS: We stably expressed the mutant in mammalian cells, and analyzed the intracellular localization of the protein. The intracellular degradation pathway was determined by pulse-chase analyses in the presence of various inhibitors of ERAD. RESULTS AND CONCLUSIONS: Endoglycosidase H digestion and immunofluorescence staining revealed the mutant being retained in the ER. Epoxomicin, a potent and specific proteasome inhibitor, and Ala-Ala-Phe-CH(2)Cl (AAF), an inhibitor of tripeptidyl peptidase II (TPPII), suppressed the intracellular degradation of the mutant by about 65% and 50%, respectively. When epoxomicin was combined with AAF, the inhibitory effect was substantially enhanced. Although castanospermine, an inhibitor of glucosidases I and II, did not affect the degradation, kifunensine, an inhibitor of ER mannosidase I, suppressed it. Thus, it appears that the Y595C mutant is degraded through more than one pathway of ERAD, including the proteasome-dependent pathway and an alternate proteasome-independent pathway where proteases such as TPPII may be involved. Production of the critical B isoform of Man(8)GlcNAc(2) targets the mutant for ERAD, however, the interaction with calnexin/calreticulin through monoglucosylated oligosaccharides may not be required for the degradation of the mutant.

Molecular basis of a hereditary type I protein S deficiency caused by a substitution of Cys for Arg474.

The molecular basis for a hereditary type I protein S (PS) deficiency was investigated. DNA sequence analysis in the proband showed a novel missense mutation substituting Cys (TGT) for Arg474 (CGT) that is a highly conserved amino acid residue among the related proteins. This missense mutation cosegregated with the type I PS deficiency in this family. Transient expression studies showed that the secretion of the recombinant Cys-mutant PS was markedly decreased compared with that of the recombinant wild-type PS, reproducing the observed phenotype of type I deficiency. Stable expression and pulse-chase experiments demonstrated an intracellular degradation and an impaired secretion of the recombinant Cys-mutant PS. Furthermore, the substitution of Arg474 by Ala or Glu, but not by Lys, markedly reduced the secretion of the recombinant PS mutants in transient expression studies, suggesting that a positively charged basic amino acid might be needed at residue 474 and might play a key role in the protein structure and conformation of the sex hormone binding globulin-homology domain of the PS molecule. We postulate that the loss of the highly conserved Arg474 might be responsible for the type I PS deficiency inherited in this family.

Detection and characterization of seven novel protein S (PROS) gene lesions: evaluation of reverse transcript-polymerase chain reaction as a mutation screening strategy.

The molecular genetic analysis of protein S deficiency has been hampered by the complexity of the protein S (PROS) gene and by the existence of a homologous pseudogene. In an attempt to overcome these problems, a reverse transcript-polymerase chain reaction (RT-PCR) mutation screening procedure was developed. However, the application of this mRNA-based strategy to the detection of gene lesions causing heterozygous type I protein S deficiency appears limited owing to the high proportion of patients exhibiting absence of mRNA derived from the mutation-bearing allele ("allelic exclusion"). Nevertheless, this strategy remains extremely effective for rapid mutation detection in type II/III protein S deficiency. Using the RT-PCR technique, a G-to-A transition was detected at position +1 of the exon IV donor splice site, which was associated with type I deficiency and resulted in both exon skipping and cryptic splice site utilization. No abnormal protein S was detected in plasma from this patient. A missense mutation (Asn 217 to Ser), which may interfere with calcium binding, was also detected in exon VIII in a patient with type III protein S deficiency. A further three PROS gene lesions were detected in three patients with type I deficiency by direct sequencing of exon-containing genomic PCR fragments: a single base-pair (bp) deletion in exon XIV, a 2-bp deletion in exon VIII, and a G0to-A transition at position -1 of the exon X donor splice site all resulted in the absence of mRNA expressed from the disease allele. Thus, the RT-PCR methodology proved effective for further analysis of the resulting protein S-deficient phenotypes. A missense mutation (Met570 to Thr) in exon XIV of a further type III-deficient proband was subsequently detected in this patient's cDNA. No PROS gene abnormalities were found in the remaining four subjects, three of whom exhibited allelic exclusion. However, the father of one such patient exhibiting allelic exclusion was subsequently shown to carry a nonsense mutation (Gly448 to Term) within exon XII.