[Hereditary disorders of the protein C system in central artery and branch arteriolar occlusions]

BACKGROUND

Resistance to activated protein C (APC) is the most common hereditary defect in patients with venous thrombosis. There are conflicting reports on the prevalence of APC resistance in patients with arterial thrombosis, e.g. coronary arteries, compared to the APC resistance prevalence among the normal population. The prevalence of APC resistance in branch retinal artery occlusion (BRAO) and central retinal artery occlusion (CRAO) is unknown.

PATIENTS AND METHODS

29 consecutive patients with arterial retinal occlusions (BRAO, n = 12; CRAO, n = 17) were included in this prospective study over a 23-months-period. We searched for APC resistance, protein C or S deficiencies, as well as for acquired vascular risk factors. Factor-V-deficient plasma and genetic analysis with a PCR method were employed for APC resistance determination. Protein C and protein S activity were determined with functional tests.

RESULTS

APC resistance was found in 3 of 29 patients (10.3%). Two of these patients had BRAO and one patient CRAO. Comparing this prevalence to the APC resistance prevalence within the normal population (9%), the difference was not statistically significant. 27 patients (93.1%) had one or more vascular risk factors (arterial hypertension = 19 [65.5%], hyperlipidaemia = 14 [48.2%], smoking = 7 [24.1%], diabetes mellitus = 5 [17.2%], carotid artery stenosis = 5 [17.2%]).

CONCLUSIONS

We could not find an increased prevalence of APC resistance in patients with CRAO or BRAO when compared to the normal population.

Retinal vascular occlusion and deficiencies in the protein C pathway

PURPOSE

To report abnormalities in the protein C pathway and other vascular occlusion risk factors in patients with retinal vascular occlusion.

METHODS

In a study, we investigated 76 consecutive patients who had in-patient evaluation of venous or arterial retinal vascular occlusion. All patients underwent comprehensive tests for coagulation disorders including determinations of protein C, protein S, lupus anticoagulants, and resistance to activated protein C and were screened for vascular disease risk factors. Resistance to activated protein C was confirmed by a polymerase chain reaction method to detect the specific factor V R506Q mutation. For comparative purposes, we also screened 209 consecutive inpatients with deep vein thrombosis from the same geographic region for resistance to activated protein C as well as protein C and protein S deficiencies.

RESULTS

Ten (29%) of 35 patients with central retinal vein occlusion (CRVO) had factor V R506Q mutation. The factor V R506Q mutation was detected in four (19%) of 21 patients with branch retinal vein occlusion. The higher frequency in factor V R506Q mutation compared with the expected 9% mutation prevalence in a white population was highly significant for the central retinal vein occlusion group but not for the branch retinal vein occlusion group. In all patients with resistance to activated protein C, the factor V R506Q mutation was detected; 16 were heterozygous, one homozygous. No cases of lupus anticoagulants, protein C, or protein S deficiencies were detected. Forty (19%) of 209 patients with deep vein thrombosis were carriers of the factor V R506Q mutation.

CONCLUSIONS

The prevalence of the factor V R506Q mutation is similar in patients with central retinal vein occlusion and patients with deep vein thrombosis and represents a relevant risk factor. Screening for this mutation is therefore recommended in all patients with central retinal vein occlusion.

Long-term management of homozygous protein C deficiency: replacement therapy with subcutaneous purified protein C concentrate

We present the case of a full-term newborn in whom purpura fulminans developed shortly after birth. A diagnosis of homozygous protein C deficiency was established based upon undetectable plasma protein C activity and antigenemia in the newborn infant, and was later confirmed by protein C gene analysis. Specific replacement therapy with intravenous protein C concentrate was started 9 days after birth. This rapidly led to the complete regression of cutaneous lesions and consumption coagulopathy. After stabilization, oral anticoagulation was initiated in association with prophylactic treatment with intravenous protein C concentrate. However, oral anticoagulation was finally abandoned as the patient presented several thrombotic and hemorrhagic episodes clearly related to difficulties with anticoagulation. Due to the hazards related to prolonged venous access, we are currently using subcutaneous infusion of protein C concentrate for the long-term management of this condition, with satisfactory results.

Inherited protein C deficiency, protein S deficiency and hyperhomocysteinaemia in a patient with hereditary spherocytosis

We report a family with hereditary spherocytosis in whom there is, in addition, a cluster of genetic predispositions to thrombosis. Although inherited prothrombotic abnormalities are prevalent in the general population, the likelihood of this combination of abnormalities being found in a single family is extremely low. The management of such high risk individuals is discussed.

Analysis of 45 episodes of arterial occlusive disease in Japanese patients with congenital protein C deficiency

Hereditary protein C deficiency is associated with a predisposition to venous thrombosis. It is not clear whether the deficiency is involved in arterial occlusion. In the present study, we screened for protein C amidolytic activity in patients admitted to the National Cardiovascular Center Hospital, and we identified among them 43 probands and 51 relatives with heterozygous protein C deficiency. Among them, 34 patients with heterozygous protein C deficiency had manifested 45 episodes of arterial occlusive disease. Venous thrombotic diseases were less common. In the examination of whether protein C deficiency hastens arterial occlusion, we found a significant difference (p =0.02) in the age at onset of acute myocardial infarction between the patients with protein C deficiency (n=10; 49.4+/-14.8 years) and a group of patients with normal protein C levels (n=42; 60.5+/-10.6 years). Acute myocardial infarction occurred before 40 years of age in a significantly greater proportion of the patients with protein C deficiency (3:10, 30%) as compared with the controls (2:42, 5%) (chi2=5.9, p=0.015). At the onset of atherothrombotic cerebral infarction the patients with protein C deficiency were significantly (p=0.022) younger (n= 11; 57.4+/-12.8 years) than those with normal protein C levels (n=48; 64.6+/-10.1 years). Venous thrombosis was the most frequent clinical manifestation (21 of 31 episodes) in the patients with antithrombin III deficiency (n=26; 68% of the total), who were admitted to our hospital. Thus, our study suggests that congenital protein C deficiency contributes to earlier onset of arterial occlusive diseases, especially acute myocardial infarction, in Japanese subjects.

Type-I protein-C deficiency caused by disruption of a hepatocyte nuclear factor (HNF)-6/HNF-1 binding site in the human protein-C gene promoter

The level and tissue specificity of eukaryotic gene transcription is determined by the binding of specific transcription factors to DNA sequence elements located around the transcription start site. The availability and activity of specific transcription factors depends on a variety of developmental and environmental cues and, therefore, varies from cell type to cell type. For instance, liver tissue, the principal site of expression of the coagulation inhibitor protein C, expresses a heterogeneous group of transcription factors called hepatocyte nuclear factors (HNFs). Some of these HNFs are essential players in protein-C gene expression. This review discusses the significance of HNF-1 and HNF-6 in regulating the transcription of the protein-C gene and gives directions for future research.

Risk of venous thromboembolism and clinical manifestations in carriers of antithrombin, protein C, protein S deficiency, or activated protein C resistance: a multicenter collaborative family study

Deficiencies of antithrombin (AT), protein C (PC) or protein S (PS), and activated protein C resistance (APCR) are very well-established coagulation defects predisposing to venous thromboembolism (VTE). We performed a retrospective cohort family study to assess the risk for VTE in individuals with AT, PC, or PS deficiency, or APCR. Five hundred thirteen relatives from 9 Italian centers were selected from 233 families in which the proband had had at least 1 episode of VTE. We calculated the incidence of VTE in the whole cohort and in the subgroups after stratification by age, sex, and defect. The overall incidence of VTE (per 100 patient-years) in the group of relatives was 0.52. It was 1.07 for AT, 0.54 for PC, 0.50 for PS, 0.30 for APCR, and 0.67 in the group with a double defect. The incidence was associated with age, but not with sex. The mean age at onset was between 30 and 40 years for all the coagulation defects. Women had the peak of incidence in the age range of 21 to 40 years, earlier than men. The lifetime risk for VTE was 4.4 for AT versus APCR, 2.6 for AT versus PS, 2.2 for AT versus PC, 1.9 for PC versus APCR, and 1.6 for PS versus APCR. AT deficiency seems to have a higher risk for VTE than the other genetic defects. There is a relation between age and occurrence of thrombosis for both men and women. The latter had the peak of incidence earlier than the former.

A molecular model of a point mutation (Val297Met) in the serine protease domain of protein C

A heterozygous GTG to ATG (Val297Met) mutation was detected in a patient with inherited protein C deficiency and deep vein thrombosis. Cosegregation of the mutation with protein C deficiency was observed through a family pedigree study. Molecular models of the serine protease domains of wild type and mutant protein C were constructed by standard comparative method. Val 297 was found to be located in the hydrophobic core of the protein. Although the substitution of Met for Val does not greatly alter the hydrophobicity of the protein, it introduces a bulkier side chain, which yields steric hindrance between this residue and adjacent residues, such as Met364, Tyr393, Ile321, Ile323, and Val378. It seems that the Met can not fit into the tight packing into which it is trapped, thereby probably inducing misfolding and/or greater instability of the protein. Such misfolding and/or instability thereby eventually disturbs the catalytic triad, in consistent with the observed type I deficiency state.

[Antithrombin deficiency and thrombosis in a young child]

BACKGROUND

Thromboses represent a rare event in children and may be due to a deficiency of antithrombin.

CASE REPORT

A 10-year-old boy developed thrombosis due to a congenital quantitative deficiency in antithrombin, confirmed by molecular biology. His father was diagnosed with the same deficiency. The child was first treated with heparin and is now on antivitamin K. He is well 26 months after diagnosis.

CONCLUSION

When a young patient presents with a thrombotic event, a congenital deficiency in one of the inhibitors of coagulation, one of which is antithrombin, should be looked for and the condition treated as soon as possible.

Incidence of venous thromboembolism in families with inherited thrombophilia

The risk of spontaneous or risk-period related venous thromboembolism in family members of symptomatic carriers of antithrombin (AT), protein C (PC) or protein S (PS) defects, as well as of the Factor V Leiden mutation is still undefined. We performed a retrospective cohort study in family members (n = 793) of unselected patients with a documented venous thromboembolism and one of these deficiencies to make an estimate of this risk. The annual incidences of total and spontaneous venous thromboembolic events in carriers of AT, PC or PS defects (n = 181) were 1.01% and 0.40%, respectively, as compared to 0.10% and 0.04% in non-carriers, respectively (relative risks both 10.6). In carriers of Factor V Leiden (n = 224), the annual incidences of total and spontaneous venous thromboembolism were 0.28% and 0.11%, respectively, as compared to 0.09% and 0.04% in non-carriers, respectively (relative risks 2.8 and 2.5). Additional risk factors (immobilisation, surgery and trauma: oral contraceptive use; and pregnancy/ post-partum) increased the risk of thrombosis in carriers of AT, PC and PS defects as compared to non-carriers (relative risks 8.3, 6.4 and 8.2, respectively). Oral contraceptive use and pregnancy/ post-partum period increased the risk of thrombosis in carriers of Factor V Leiden to 3.3-fold and 4.2-fold, respectively, whereas other risk factors had only a minor effect. These data lend some support to the practice of screening family members of symptomatic carriers of a AT, PC and PS deficiency. For family members of symptomatic carriers of Factor V Leiden, screening does not seem to be justified except for women in fertile age.

[Screening methods in genetic diagnosis of hereditary protein C deficiency]

Genomic analysis and detailed blood coagulation examinations of 22 family members of 18 families with repeatedly low protein C activity have been performed. Blood coagulation examinations: INR, fibrinogen, plasminogen, alpha-2-antiplasmin, lupus anticoagulant, APC resistance test, protein C activity and antigen, protein S activity and antithrombin activity. Genetic examinations: the presence of FII G20210A alle and FV:Q506 Leiden mutation were examined and for the mutation screening in the protein C gene combination of polymerase chain reaction (PCR) with denaturing gradient gelelectrophoresis (DGGE) or with single-strand conformation polymorphism (SSCP) analysis has been performed. The amplified DNA fragments with aberrant migration during DGGE and SSCP analysis were sequenced. Nine family members of seven families were identified carrying mutations in the protein C gene: one nonsense mutation in exon VII (Arg 157-Stop), two types of missense mutations in four patients in exon IXA (230 Arg-Lys, 254 Thr-Ile, the latter is a new mutation, Protein C Pécs), one missense mutation in two patients in exon IXB (325 Val-Ala), one missense mutation in exon IXC (359 Asp-Asn) and a rare frameshift deletion in exon IXC (364 Met-Trp, 378 Stop). Nine families were evaluated carrying no mutation in their protein C gene, but other genetic or blood coagulation disturbances have been identified, eight of them had borderline decrease in their protein C activity (60-70%). The presence of FV:Q506 mutation could be diagnosed in eight families (in 3 cases homozygous, in 5 cases heterozygous form), among them combination of the defects could be proved in three of the eight families: FV:Q506 Leiden mutation with antiphospholipoid antibodies in 2 families and the presence of Leiden mutation with prothrombin gene mutation in 1 family. Protein S deficiency in combination with prothrombin gene mutation has been identified in 1 family. There were 2 families where no genetic or blood coagulation alterations could be detected in the background of the repeatedly low protein C activity. Large deletions or insertions which are not detectable by our screening methods could not be excluded in these families and therefore sequencing of the total protein C gene had been performed with negative results. According to the literature and our experience the screening methods that were administered in this study are suitable for the detection of mutations in the protein C gene.

Thrombophilia as a multigenic disease

BACKGROUND AND OBJECTIVE

Venous thrombosis is a common disease annually affecting 1 in 1000 individuals. The multifactorial nature of the disease is illustrated by the frequent identification of one or more predisposing genetic and/or environmental risk factors in thrombosis patients. Most of the genetic defects known today affect the function of the natural anticoagulant pathways and in particular the protein C system. This presentation focuses on the importance of the genetic factors in the pathogenesis of inherited thrombophilia with particular emphasis on those defects which affect the protein C system.

INFORMATION SOURCES

Published results in articles covered by the Medline database have been integrated with our original studies in the field of thrombophilia.

STATE OF THE ART AND PERSPECTIVES

The risk of venous thrombosis is increased when the hemostatic balance between pro- and anti-coagulant forces is shifted in favor of coagulation. When this is caused by an inherited defect, the resulting hypercoagulable state is a lifelong risk factor for thrombosis. Resistance to activated protein C (APC resistance) is the most common inherited hypercoagulable state found to be associated with venous thrombosis. It is caused by a single point mutation in the factor V (FV) gene, which predicts the substitution of Arg506 with a Gln. Arg506 is one of three APC-cleavage sites and the mutation results in the loss of this APC-cleavage site. The mutation is only found in Caucasians but the prevalence of the mutant FV allele (FV:Q506) varies between countries. It is found to be highly prevalent (up to 15%) in Scandinavian populations, in areas with high incidence of thrombosis. FV:Q506 is associated with a 5-10-fold increased risk of thrombosis and is found in 20-60% of Caucasian patients with thrombosis. The second most common inherited risk factor for thrombosis is a point mutation (G20210A) in the 3' untranslated region of the prothrombin gene. This mutation is present in approximately 2% of healthy individuals and in 6-7% of thrombosis patients, suggesting it to be a mild risk factor of thrombosis. Other less common genetic risk factors for thrombosis are the deficiencies of natural anticoagulant proteins such as antithrombin, protein C or protein S. Such defects are present in less than 1% of healthy individuals and together they account for 5-10% of genetic defects found in patients with venous thrombosis. Owing to the high prevalence of inherited APC resistance (FV:Q506) and of the G20210A mutation in the prothrombin gene, combinations of genetic defects are relatively common in the general population. As each genetic defect is an independent risk factor for thrombosis, individuals with multiple defects have a highly increased risk of thrombosis. As a consequence, multiple defects are often found in patients with thrombosis.

[Hereditary deficiency of antithrombin III, protein C, protein S and factor XII in 121 patients with venous or arterial thrombosis]

INTRODUCTION

Hereditary thrombophilia is caused by various inherited disorders which lead to familial tendency to recurrent venous thrombosis usually at an early age and with spontaneous onset. In the studies reported so far, the different prevalence of hereditary thrombophilia among patients with venous thrombosis was found, greatly depending on criteria for selection of patients. Arterial thrombosis is most often the consequence of arteriosclerosis but the prevalence of hereditary thrombophilia among young patients with arterial thrombosis and without recognized risk factors for arteriosclerosis is not known . In this study, the frequency of hereditary deficiencies of antithrombin III (AT III), protein C (PC), protein S (PS), plasminogen (PLMG), factor XII (F XII) and dysfibrinogenaemia was investigated over a 2-year period in 121 patients with venous or arterial thrombosis selected according to the recommendations of the British Committee for Standards in Haematology.

PATIENTS AND METHODS

The study included total a of 121 patients (58 males and 63 females) with documented venous or arterial thrombosis. Table 1 shows patient's characteristics regarding gender, age and clinical manifestation of thrombosis. Each patient fulfilled at least one of the following criteria: a) venous thrombosis prior to the age of 45; b) arterial thrombosis prior to the age of 30, without risk factors for arteriosclerosis; c) recurrent thrombosis; d) familial tendency to thrombosis; e) thrombosis of unusual localization. A detailed history was taken from each patient on earlier personal or familial occurrence of thrombosis. For the purpose of this study, thrombophilia was characterized as congenital when the deficient protein was constantly below normal value and when the same deficiency was confirmed in a close family member; acquired when the acquired disorder predisposing to thrombosis was present in absence of constant protein deficiency; and idiopathic when the cause of thrombosis was unknown. All tests were performed in plasma obtained after centrifugation of venous blood anticoagulated with 0.129 mol/1 sodium citrate. Concentrations of fibrinogen, PT, PTT and F XII were measured by standard clotting methods. At III, PC and plasminogen activity were determined by chromogenic methods using commercial reagents (Boehring, Marburg, Germany). AT III, PC and total PS antigen were assayed by Laurell immunoelectrophoresis. The presence of lupus anticoagulant was investigated by recommended tests.

RESULTS

A total of 15 patients (12.4%) fulfilled criteria for hereditary thrombophilia. Seven of them (5.8%) had AT III deficiency, five (4.1%) PC deficiency, two (1.6%) PS deficiency, and one patient had F XII deficiency. Secondary thrombophilia was found in 21.5% of patients and the cause of thrombosis in 66.1% of patients was not elucidated. A high frequency of hereditary thrombophilia has been found in patients with arterial thrombosis (40%). Among patients with hereditary thrombophilia thrombosis occurred at significantly younger age (29.9 vs. 42.2 and 40.9 yr.) compared to the patients with secondary and idiopathic thrombophilia, respectively. Patients with hereditary thrombophilia had also a higher occurrence of positive family history related to thrombosis (66.7% vs. 7.7% and 27.5%).

DISCUSSION

The prevalence of hereditary thrombophilia in nonselected patients with venous thrombosis is relatively low, and for that reason the selection of patients, according recommended criteria, in whom the screening tests for congenital thrombophilia should be performed, is strongly suggested by many authors. In our study we used the generally accepted recommendations for investigation of patients with venous and arterial thrombosis. The presence of congenital thrombophilia was found in 15 (12.4%) of 121 studied patients, what is in accordance with results of other similarly designed studies. (ABSTRACT TRUNCATED)

Genetic analysis of protein C deficiency in nineteen Japanese families: five recurrent defects can explain half of the deficiencies

We have been studying the molecular basis of protein C deficiency. In this study, we determined the molecular defects of protein C deficiency in 19 Japanese families by using a strategy combining polymerase chain reaction (PCR) and single-strand conformational polymorphism (SSCP) analysis. We identified 10 missense mutations, 1 in-frame deletion, 1 frameshift deletion, 1 frameshift addition, and 1 splice site mutation, 5 of which were novel. From the results of genetic analysis of 67 Japanese families with protein C deficiency reported in this and previous studies, the recurrent defects including Phe139Val and Met365Ile substitutions and a Lys150 d letion, a G8857 deletion, and a splice site mutation of G3079A were only found in Japanese subjects and seemed to be a founder effect. In contrast, Arg169Trp, Arg286His, Val297Met, and Asp359Asn substitutions, all occurring at CG dinucleotides, were commonly observed in not only Japanese but also Western populations, indicating that these are hot spots for mutation in the protein C gene. These 9 recurrent molecular defects were found in 43 families in total, accounting 64% of Japanese families with protein C deficiency. In particular, the recurrent defects of Phe139Val, Arg169Trp, Va1297Met, and Met36-4Ile substitutions and a G8857 deletion were found in 33 families in total, accounting for 49% of Japanese families with protein C deficiency. For the identification of the genetic defect in Japanese patients with protein C deficiency, screening of these recurrent defects by using restriction enzyme cleavage is a rational method.

Hereditary thrombophilia and venous thromboembolism

The hereditary thrombophilias are a group of inherited conditions that predispose to thrombosis. Heritable deficiencies of the endogenous anticoagulants protein C, protein S, and antithrombin have been recognized for some years, but their prevalence, even among patients with familial thrombosis, is low. The recent discoveries of two relatively common thrombophilias, resistance to activated protein C associated with an abnormal factor V gene (factor V Leiden), and prothrombin gene variant 20210A, have substantially increased the likelihood of identifying a heritable predisposing factor in patients with thromboembolism. Modestly elevated levels of plasma homocysteine, which are in part genetically determined, have also recently been associated with an increased risk for venous thromboembolism. A predisposition to thrombosis can now be identified in a substantial minority of patients with venous thromboembolism, and in the majority of patients with familial thrombosis, and there is accumulating evidence that multiple coexisting defects are present in persons with the most marked tendency to thrombosis. The most common causes of hereditary thrombophilia are reviewed with an emphasis on resistance to activated protein C, prothrombin variant 20210A, and hyperhomocystinemia, and the current status of laboratory testing for thrombophilia is discussed.

Ischemic stroke in a young patient with protein C deficiency and prothrombin gene mutation G20210A

We report a patient who had an ischemic stroke aged 22 years, an inherited type I protein C deficiency and a heterozygous genotype of prothrombin gene 20210A. In view of recent reports of an increased risk for ischemic cerebral vascular disease in patients with the prothrombin 20210A mutation, we suggest that many of the reported cases of ischemic stroke and protein C deficiency may have had additional prothrombotic disorders such as the prothrombin mutation. The current data concerning the magnified risk for stroke in patients with the prothrombin 20210A mutation suggests the need to study all patients with premature stroke for this mutation and the other risk factors for thrombosis. This would include homocysteine, lupus inhibitor, anticardiolipin antibodies, and possibly the natural inhibitors of coagulation. It is possible that patients with the prothrombin 20210A mutation and ischemic cerebral vascular disease would benefit from long-term anticoagulation therapy in a similar way to patients with the antiphospholipid syndrome.

[Thrombophilia caused by congenital disorders of blood coagulation]

Today, more than 40% of all patients who develop a thrombosis are found to have inherited thrombophilia. The most common cause of this is APC resistance, which can usually be traced back to factor V-Leiden. In the commonly heterozygous patients the risk of thrombosis is increased about 7-fold (life-long risk of thrombosis 10 to 15%). In most cases, however, additional thrombogenic stimuli are required (oral contraception, pregnancy, surgery, immobilization). In combination with oral contraceptives, the risk is increased roughly 30-fold. In contrast, APC resistance does not present an increased risk for thrombosis in the arterial system (myocardial infarction, stroke). Four further inherited or acquired disorders of the hemostatic system are known: prothrombin dimorphism, antithrombin, protein C and protein S deficiencies. Prothrombin dimorphism, the second most common form of inherited thrombophilia, has been known only for the past two years and elevates the risk of thrombosis only to a moderate degree. Today, a search for thrombophilic factors should be carried out not only in young patients with spontaneous development of thrombosis, but also in elderly patients, even when an additional risk for the occurrence of thrombosis such as traumatization or immobilization is present. Therapeutic consequences are discussed.

Inactivation of the gene for anticoagulant protein C causes lethal perinatal consumptive coagulopathy in mice

Matings of mice heterozygous for a protein C (PC) deficient allele, produced by targeted PC gene inactivation, yielded the expected Mendelian distribution of PC genotypes. Pups with a total deficiency of PC (PC-/-), obtained at embryonic day (E) 17.5 and at birth, appeared to develop normally macroscopically, but possessed obvious signs of bleeding and thrombosis and did not survive beyond 24 h after delivery. Microscopic examination of tissues and blood vessels of E17.5 PC-/- mice revealed their normal development, but scattered microvascular thrombosis in the brain combined with focal necrosis in the liver was observed. In addition, bleeding was noted in the brain near sites of fibrin deposition. The severity of these pathologies was exaggerated in PC-/- neonates. Plasma clottable fibrinogen was not detectable in coagulation assays in PC-/- neonatal mice, suggestive of fibrinogen depletion and secondary consumptive coagulopathy. Thus, while total PC deficiency did not affect the anatomic development of the embryo, severe perinatal consumptive coagulopathy occurred in the brain and liver of PC-/- mice, suggesting that a total PC deficiency is inconsistent with short-term survival.

Different risks of thrombosis in four coagulation defects associated with inherited thrombophilia: a study of 150 families

Deficiency of the naturally occurring anticoagulant proteins, such as antithrombin, protein C and protein S, and activated protein C resistance due to the factor V Leiden gene mutation is associated with inherited thrombophilia. So far, no direct comparison of the thrombotic risk associated with these genetic defects is available. In this study, we wish to compare the lifetime probability of developing thrombosis, the type of thrombotic symptoms, and the role of circumstantial triggering factors in 723 first- and second-degree relatives of 150 index patients with different thrombophilic defects. We found higher risks for thrombosis for subjects with antithrombin (risk ratio 8.1, 95% confidence interval [CI], 3.4 to 19.6), protein C (7.3, 95% CI, 2.9 to 18.4) or protein S deficiency (8.5, 95% CI, 3. 5 to 20.8), and factor V Leiden (2.2, 95% CI, 1.1 to 4.7) than for individuals with normal coagulation. The risk of thrombosis for subjects with factor V Leiden was lower than that for those with all three other coagulation defects (0.3, 95% CI, 0.1 to 1.6), even when arterial and superficial vein thromboses were excluded and the analysis was restricted to deep vein thrombosis (0.3, 95% CI, 0.2 to 0.5). No association between coagulation defects and arterial thrombosis was found. The most frequent venous thrombotic manifestation was deep vein thrombosis with or without pulmonary embolism (90% in antithrombin, 88% in protein C, 100% in protein S deficiency, and 57% in factor V Leiden), but a relatively mild manifestation such as superficial vein thrombosis was common in factor V Leiden (43%). There was a predisposing factor at the time of venous thromboembolism in approximately 50% of cases for each of the four defects. In conclusion, factor V Leiden is associated with a relatively small risk of thrombosis, lower than that for antithrombin, protein C, or protein S deficiency. In addition, individuals with factor V Leiden develop less severe thrombotic manifestations, such as superficial vein thrombosis.

Inherited prothrombotic states and ischaemic stroke in childhood

OBJECTIVE

To investigate the prevalence of currently recognised inherited prothrombotic states in a population of children with arterial stroke.

METHODS

Children with arterial stroke presenting to a tertiary level paediatric neurology centre between 1990 and 1996 were investigated for inherited prothrombotic states.

RESULTS

Sixty seven children with arterial stroke were investigated. Abnormalities were initially identified in 16 patients; however, only eight children (12%) had an inherited prothrombotic state. This was type 1 protein S deficiency in one patient, the factor V Leiden mutation in six, and activated protein C resistance (without the factor V Leiden mutation) in one. The prevalence of the factor V Leiden mutation was not significantly higher in children with arterial stroke (12%) than in a control population of children without thrombosis attending the same institution (5.2%; Fisher's exact test, p=0.19; difference in prevalence between patients and controls (95% confidence interval)=6.8% (-2.78% to 16.8%)).

CONCLUSIONS

Currently recognised inherited prothrombotic tendencies were rarely associated with stroke in this group of children, although larger numbers of patients would be needed to confirm this. Age appropriate normal values should be used when interpreting the results of a prothrombotic screen. Prothrombotic abnormalities seen acutely are as often transient as inherited. Longitudinal assessment and family studies are required before low concentrations of an anticoagulant protein found acutely can be attributed to an inherited abnormality.

Type I protein C deficiency in French Canadians: evidence of a founder effect and association of specific protein C gene mutations with plasma protein C levels

Protein C (PROC) deficiency is one of the most common autosomal codominant diseases. Although more than 150 germline mutations in the PROC gene have been described around the world, the spectrum of mutations among French Canadians is unknown. We have identified one frameshift (3363 ins C) and two missense mutations (R178Q and T298M) in 7 French Canadian families with type I PROC deficiency. In order to demonstrate a possible founder effect for the 3363 ins C mutation, we have constructed a high-resolution genetic map to locate several highly polymorphic markers close to PROC locus. We have then genotyped five markers in 36 heterozygotes for the 3363 ins C mutation. Our data suggest that these patients carry a common haplotype at the PROC locus. Immunologic plasma PROC levels of heterozygotes and genetically normal relatives were also correlated with the nature of the mutation in the coding sequence and with the genotype of three polymorphisms in the PROC promoter. We found that the mean immunologic plasma PROC levels were lower in heterozygotes for the frameshift mutation 3363 ins C compared to heterozygotes for one of the two missense mutations R178Q and T298M (0.46 vs 0.61; P = 0.0004). Moreover, this difference cannot be explained by the genetic variation of the three polymorphisms in the PROC promoter which accounts for only 10.4% of the variation of immunologic PROC levels in non-deficient subjects. These results suggest that the nature of the mutation in the coding sequence of PROC gene may modulate immunologic plasma PROC levels.

Chilblains and Raynaud phenomenon are usually not a sign of hereditary protein C and S deficiencies

Hereditary protein C and S deficiencies are risk factors for thrombosis. They are associated with purpura fulminans and coumarin-induced skin necrosis. Recently, necrotic livedo of the extremities, severe chilblains and severe frostbite have been observed in protein C or S deficient patients. Our study was designed to evaluate the prevalence of cold-induced acral manifestations in patients with protein C or S deficiency. One-hundred-and-six patients with protein C or S deficiency and controls matched for sex and age were studied by questionnaire. Data included any history of acral manifestation possibly related to cold exposure, i.e. chilblains, Raynaud phenomenon, acrocyanosis and possible associated factors. Assessment of the diagnosis by a dermatologist was recorded. No difference was found in the prevalence of acral manifestations between patients and controls. This study suggests that protein C and S deficiencies are not risk factors for cold-induced acral manifestations.