Plasminogen and tissue-type plasminogen activator deficiency as risk factors for thromboembolic disease

Plasminogen Deficiency: A Case Report and Review

Plasminogen deficiency, a rare disorder characterized by impaired fibrinolysis, frequently results in ligneous conjunctivitis. In this report, we report a case of a Saudi girl manifesting both conjunctivitis and hydrocephalus. Her initial symptoms at 1 month of age were recurring eye redness, which was inaccurately diagnosed as simple conjunctivitis. Surgical intervention for her ocular lesions revealed underlying membrane deposition. She later exhibited signs of increased intracranial pressure, resulting in a hydrocephalus diagnosis and subsequent surgery. Genetic analysis confirmed the presence of plasminogen deficiency. Clinical evaluations highlighted ligneous conjunctivitis, variations in visual acuity, and facial acne. Laboratory assessments demonstrated diminished plasminogen levels. The therapeutic approach encompassed plasminogen replacement, administered intravenously (1000 units, thrice weekly) and as eye drops, with the potential addition of fresh frozen plasma. Notably, this replacement therapy led to a significant reduction in hospital admissions and the severity of her conjunctivitis. Given the challenges in procuring consistent plasminogen supplies, the viability of hepatic transplantation is currently under investigation.

Mechanisms of thrombosis in ANCA-associated vasculitis

Patients with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) have a two- to threefold greater risk of developing venous as well as arterial thrombotic events. Although such thrombotic events are more commonly seen during phases of active AAV, they are also recognized to occur during AAV in remission. Endothelial injury is a key pathogenic event in AAV. Endothelial injury can be caused by neutrophil activation and release of thrombogenic tissue factor into the circulation. Neutrophil activation further results in the formation of neutrophil extracellular traps (NETs). NETs contribute to thrombosis by expressing tissue factor. NETs have also been detected in cutaneous thrombi from patients with AAV induced by hydralazine. Activated neutrophils in AAV patients release thrombogenic microparticles loaded with tissue factor which further enhances clotting of blood. Antiphospholipid antibodies (APLs) have been detected in up to a third of AAV and might also be induced by drugs such as cocaine adulterated with levamisole and propylthiouracil, which are known to trigger AAV. Such APLs further drive the thrombosis in AAV. Once thrombogenesis occurs, the homeostatic mechanisms resulting in clot dissolution are further impaired in AAV due to anti-plasminogen antibodies. The ongoing pandemic of coronavirus disease 2019 (COVID-19) is associated with endothelial injury and NETosis, mechanisms which are in common with AAV. Reports of new-onset AAV following COVID-19 have been described in the literature, and there could be shared mechanisms driving these processes that require further evaluation.

Thrombin and plasmin generation in patients with plasminogen or plasminogen activator inhibitor type 1 deficiency

INTRODUCTION

Deficiencies of plasminogen and plasminogen activator inhibitor type 1 (PAI-1) are rare disorders of fibrinolysis. Current laboratory assays for analysis of activity of plasminogen and PAI-1 do not provide an accurate correlation with clinical phenotype.

METHODS

The Nijmegen Hemostasis Assay (NHA) was used to simultaneously measure thrombin and plasmin generation in 5 patients with plasminogen deficiency (PLGD) and 10 patients with complete PAI-1 deficiency. Parameters analysed included: lag time ratio, thrombin peak time ratio, thrombin peak height, thrombin potential (AUC), fibrin lysis time, plasmin peak height and plasmin potential. Parameters were expressed as a percentage compared to a reference value of 53 healthy normal controls.

RESULTS

Patients with PLGD demonstrated a short lag time and thrombin peak time, with normal thrombin peak height but an increased AUC. Plasmin generation was able to be detected in only one (23% plasminogen activity) of the five PLGD patients. All ten PAI-1 deficient patients demonstrated a short lag and thrombin peak time, low thrombin peak height with normal AUC. Plasmin generation revealed an increased plasmin peak and plasmin potential; interestingly, there was a large variation between individual patients despite all patients having the same homozygous defect.

CONCLUSION

Patients with either PLGD or PAI-1 deficiency show distinct abnormalities in plasmin and thrombin generation in the NHA. The differences observed in the propagation phase of thrombin generation may be explained by plasmin generation. These results suggest that disorders of fibrinolysis also influence coagulation and a global assay measuring both activities may better correlate with clinical outcome.

Impaired plasminogen binding in patients with venous thromboembolism: Association with protein carbonylation

INTRODUCTION

Venous thromboembolism (VTE) is associated with hypofibrinolysis. Its mechanisms are poorly understood. We investigated plasminogen-fibrin interaction and its association with fibrinolytic capacity and protein oxidation/carbonylation in VTE patients.

MATERIALS AND METHODS

Plasma-purified plasminogen conversion to plasmin and surface plasmon resonance employed for plasminogen-fibrin interactions were individually evaluated in all healthy controls and non-anticoagulated patients following VTE, 10-23months since the event. We also assessed plasma fibrin clot permeability (K_s), clot lysis time (LT), activators and inhibitors of fibrinolysis together with oxidation/carbonylation markers.

RESULTS

VTE patients had impaired plasminogen binding to fibrin (apparent Kd, +290%, p=0.002), reduced rate of plasmin generation (-4.7%, p=0.001), and longer LT (+18.6%, p<0.001) compared with controls. Fibrinogen and K_s were similar in both groups. Apparent Kd correlated with LT (r=0.43, p=0.037), tissue plasminogen activator-plasminogen activator inhibitor 1 (tPA-PAI-1) complexes (r=0.63, p=0.012), and active PAI-1 (r=0.49, p=0.03). Compared with controls, VTE patients had higher thiobarbituric acid reactive substances (TBARS), total protein carbonyl content (PC), and lower total antioxidant capacity (all p<0.001), that all were associated with LT (r=0.61, r=0.56, and r=-0.47, respectively, all p<0.05). Impaired plasminogen binding to fibrin reflected by apparent Kd positively correlated with TBARS (r=0.48, p=0.032) and PC (r=0.54, p=0.013) in the whole group.

CONCLUSIONS

Plasminogen-fibrin interactions are altered in young and middle-aged VTE patients, without known thrombophilias, except increased factor VIII. The mechanisms underlying these phenomena remain to be established.

Structure-based antigenic epitope and PEGylation improve the efficacy of staphylokinase

Staphylokinase (Sak) holds promise for use in thrombolytic therapy for acute myocardial infarction. However, its immunogenicity is a major disadvantage under clinical conditions. PEGylation has become a sophisticated method to decrease that immunogenicity. In this report, according predicted epitope from the active center, five residues, including Gly79, Leu82, Lys84, Ala97, and Arg104 have been mutant as cysteine for mono PEGylation, respectively. According to the relative immunogenicity of Sak or its PEGylation derivatives, the amount of specific anti-Sak IgG antibodies elicited by PEGylation proteins, including C79G, C82L, C84K, C97A, and C104R in BALB/c mice decreased by approximately 15–75% each. PEGylated Sak derivatives showed a decrease of up to 75% in the immune reactivity in PEG-Sak-C104R. Thrombelastography experiments showed that two PEG-conjugated derivatives, PEG-Sak-C97A (Ly30, 68.14 ± 2.51%) and PEG-Sak-C104R (Ly30, 66.49 ± 5.97%), the LY30 of PEG-Sak-C97A, and PEG-Sak-C104R produced values very similar to those of wild-type Sak. The fibrin plate assays showed the bioactivity of PEG-Sak-C104R to exhibit the most activity approximately as much as urokinase (diameter of halo pattern, 18.6 ± 1.06 mm) and tPA (diameter of halo pattern, 17.2 ± 0.49 mm). The Sak PEGylation derivative PEG-Sak-C104R was also selected for further in vivo activity experimentation. The thrombolytic ability of PEG-Sak-C104R is a little lower than wild-type Sak, whereas, this PEGylated protein retained high activity suitable for thrombolytic therapy. Collectively, with the in vivo and in vitro experiments, the present study suggests that site mutant PEGylation, PEG-Sak-C104R, is a suitable type of PEGylation for clinical applications. Further optimization would help maintain the bioactivity and decrease the immunogenicity of staphylokinase.

Changes to fibrinolysis in patients with systemic lupus erythematosus are associated with endothelial cell damage and inflammation, but not antiphospholipid antibodies

We investigated whether changes to fibrinolysis were associated with other manifestations of systemic lupus erythematosus (SLE), including antiphospholipid (APL) antibody status, endothelial damage, and inflammation. Ninety-four patients (36 SLE patients, 58 healthy controls) were recruited from Tasmania, Australia. Circulating levels of plasminogen, α2-antiplasmin, tissue-type plasminogen activator, plasminogen activator inhibitor-1, and thrombin-activatable fibrinolysis inhibitor (TAFI) were measured, as well as APL antibodies (including lupus anticoagulant, anticardiolipin, and antibeta-2 glycoprotein-1 antibodies), soluble E-selectin, and interleukin-6. Whereas there was a significant decrease in plasminogen (patient vs. control; median) (210 vs. 444 ng/ml; P < 0.0001) and increase in α2-antiplasmin (0.53 vs. 0.09 μg/ml; P = 0.0007), there was increased t-PA (0.65 vs. 0.40 ng/ml; P = 0.0001) and decreased TAFI (8.8 vs. 10.0 ng/ml; P = 0.002) in SLE patients compared to healthy controls. Plasminogen was significantly associated with α2-antiplasmin (rho = -0.563, P < 0.001); TAFI (rho = 0.410, P = 0.011); soluble E-selectin (rho = 0.531, P = 0.001); and interleukin-6 (rho = 0.489, P = 0.002) in SLE patients; however, APL antibody status was not associated with any of the markers measured. This study has demonstrated that fibrinolysis is significantly altered in patients with SLE compared to controls, and associated with endothelial cell damage and inflammation, but not APL antibody status.

Cardiometabolic biomarkers are predictors of readmission and death in patients hospitalized for acute dyspnea

Background

Acute dyspnea affects a large heterogeneous patient group with high mortality and readmission rates.

Purpose

To investigate if cardiometabolic biomarkers and clinical characteristics predict readmission and death in patients hospitalized for acute dyspnea.

Methods

65 dyspnea patients at a general internal medicine ward were followed for six months. The combined endpoint was readmission or death.

Measurements and results

Cardiometabolic biomarkers at admission were related to the endpoint in Cox proportional hazard models (adjusted for sex, age, oxygen saturation, respiratory rate and C-reactive protein (CRP)). The biomarkers tissue-type plasminogen activator (tPA), prolactin (PRL), tumor necrosis factor receptor superfamily member 6 (FAS) and C-C motif chemokine 3 (CCL3) were independently and significantly related to the endpoint and combined into a biomarker risk score (BRS). Each SD increment of the BRS conferred a hazard ratio (HR) of 2.13 (1.39–3.27) P = 0.001. The top vs bottom tertile of the BRS conferred a HR of 4.75 (1.93–11.68) P = 0.001. Dyspnea severity was also associated with worse outcome, HR = 3.43 (1.28–9.20) P = 0.014. However, when mutually adjusted the BRS remained significant (P = 0.004) whereas dyspnea severity was not. The BRS was related to the endpoint among patients with mild to moderate dyspnea (P = 0.016) but not among those with severe dyspnea.

Conclusion

A score of tPA, PRL, FAS and CCL3 predicts 6-month death and readmission in patients hospitalized for acute dyspnea and may prove useful to optimize length of stay and follow-up. Although the BRS outweighs dyspnea severity in prediction of the endpoint, its prognostic role is strongest in mild-moderate dyspnea.

The fibrinolytic system-more than fibrinolysis?

The fibrinolytic system, known for its ability to regulate the activation of the zymogen plasminogen into active plasmin, has been primarily associated with the removal of fibrin and blood clots. Tissue-type plasminogen activator, the most well-recognized plasminogen activator, was harnessed for therapeutic benefit against thromboembolic disorders more than 30 years ago, whereas inhibition of this system has been proven effective for certain bleeding disorders. However, in recent years, new and unexpected functional roles for this system have been identified mostly in relation to the central nervous system that are both unrelated and independent of fibrin degradation and clot removal. Hence, it seems reasonable to ask whether agents used to modify components or activities of the fibrinolytic system have any clinical consequences unrelated to their intended use in hemostasis. This review will provide an overview of these new features of the fibrinolytic system and will also focus on prospective considerations in the use of fibrinolytic and antifibrinolytic agents.

The association between thrombophilic gene mutations and recurrent pregnancy loss

PURPOSE

To determine whether the Factor V (1691G/A), Factor V HR2 (4070A/G), Prothrombin (20210G/A), PAI-1 (-675 I/D, 5G/4G), ACE (intron 16 I/D), Factor VII (Gln353Arg), Factor XIII (Val34Leu), β-fibrinogen (-455G/A), Glycoprotein Ia (807C/T), tPA (intron 8 D/I) gene mutations could be risk factors for recurrent pregnancy loss (RPL).

METHODS

Genotyping of thrombophilic gene mutations were carried out by amplification Refractory Mutation System-PCR (ARMS-PCR) method after DNA extraction.

RESULTS

We found that the mutant allele frequencies of Factor V (1691G/A), Factor V HR2 (4070A/G), Prothrombin (20210G/A), PAI-1 (-675 I/D, 5G/4G), Factor XIII (Val34Leu) and β-fibrinogen (-455G/A) were more seen in the case group compared with the healthy control; However, the difference between the two group is not statistically significant (p > 0.05). Whilst the mutant allele frequencies of other studied genes were lower in the case in comparison to the fertile control women (p > 0.05).

CONCLUSION

Taken together, our data has shown that the prevalence of thrombophilic gene mutations was similar in women with RPL and healthy controls. Therefore, it appears that further studies on large-scale population and other genetic variants will be needed to conclusively find candidate genes for RPL unknown etiology in the future.

Venous thrombosis risk associated with plasma hypofibrinolysis is explained by elevated plasma levels of TAFI and PAI-1

Elevated plasma clot lysis time (CLT) increases risk of venous and arterial thrombosis. It is unclear which fibrinolytic factors contribute to thrombosis risk. In 743 healthy control subjects we investigated determinants of CLT. By comparison with 770 thrombosis patients, we assessed plasma levels of fibrinolytic proteins as risk factors for a first thrombosis. Plasminogen activator inhibitor-1 (PAI-1) levels were the main determinants of CLT, followed by plasminogen, thrombin-activatable fibrinolysis inhibitor (TAFI), prothrombin, and α2-antiplasmin. Fibrinogen, factor VII, X, and XI contributed minimally. These proteins explained 77% of variation in CLT. Levels of the fibrinolytic factors were associated with thrombosis risk (odds ratios, highest quartile vs lowest, adjusted for age, sex, and body mass index: 1.6 for plasminogen, 1.2 for α2-antiplasmin, 1.6 for TAFI, 1.6 for PAI-1, and 1.8 for tissue plasminogen activator [t-PA]). Adjusting for acute-phase proteins attenuated the risk associated with elevated plasminogen levels. The risk associated with increased t-PA nearly disappeared after adjusting for acute-phase proteins and endothelial activation. TAFI and PAI-1 remained associated with thrombosis after extensive adjustment. In conclusion, CLT reflects levels of all fibrinolytic factors except t-PA. Plasminogen, TAFI, PAI-1, and t-PA are associated with venous thrombosis. However, plasminogen and t-PA levels may reflect underlying risk factors.

Plasminogen deficiency

Plasminogen (plg) deficiency has been classified as (i) hypoplasminogenemia or 'true' type I plg deficiency, and (ii) dysplasminogenemia, also called type II plg deficiency. Both forms, severe hypoplasminogenemia and dysplasminogenemia, are not causally linked to venous thrombosis. Dysplasminogenemia does not lead to a specific clinical manifestation and probably represents only a polymorphic variation in the general population, mainly in Asian countries. Severe hypoplasminogenemia is associated with compromised extracellular fibrin clearance during wound healing, leading to pseudomembraneous (ligneous) lesions on affected mucous membranes (eye, middle ear, mouth, pharynx, duodenum, upper and lower respiratory tract and female genital tract). Ligneous conjunctivitis is by far the most common clinical manifestation. More than 12% of patients with severe hypoplasminogenemia exhibit congenital occlusive hydrocephalus. In milder cases of ligneous conjunctivitis, topical application of plg-containing eye drops, fresh frozen plasma, heparin, corticosteroids or certain immunosuppressive agents (such as azathioprine) may be more or less effective. Oral treatment with sex hormones was successful in two female patients with ligneous conjunctivitis. In severe cases with possibly life-threatening multi-organ involvement, true therapeutic options are not available at present. The plg-knockout mouse is a useful tool to study the many different properties of plg in a variety of settings, such as wound healing, tissue repair and tissue remodeling, virulence and invasiveness of certain bacteria in the human host, tumor growth and dissemination, as well as arteriosclerosis.

Ligneous conjunctivitis: a clinicopathological, immunohistochemical, and genetic study including the treatment of two sisters with multiorgan involvement

Ligneous conjunctivitis (LC) is a rare disease characterized by wood-like pseudomembranes developing on the ocular and extraocular mucosae secondary to plasminogen (PLG) deficiency. In this paper, we report two cases of LC in two sisters of 57 and 62 years of age that presented with recurrent, bilateral pseudomembranes on conjunctiva and a history of consanguinity and deafness. Pseudomembranes showed superficial and/or subepithelial deposits of eosinophilic amorphous hyaline, amyloid-like material with a variable proportion of granulation tissue, and inflammatory cells. The eosinophilic deposits were negative for Congo red stain, immunoreactive for fibrinogen, and consistently negative for amyloid A component, transthyretin, beta(2)-microglobulin, albumin, fibronectin, collagen type IV, vimentin, and cytokeratins. Among inflammatory cells, a percentage of positivity of roughly 60% for lymphocytes T (CD3+) and 40% for lymphocytes B (CD8+), with a relation of cytotoxic/helper (CD8/4) T cells of 3:2, was found. In one case, nasal polyps and recurrent gastric peptic ulcer were also characterized by the same subepithelial hyaline deposits. A novel homozygous point mutation c.1856 C>T was found in exon 15 of the PLG gene in both patients. Amniotic membrane transplantation was done in one case with promising results.

Fibrinolysis and the risk of venous and arterial thrombosis

PURPOSE OF REVIEW

The fibrinolytic system is often regarded as just an innocent bystander in the pathogenesis of venous and arterial thrombosis, while (hyper)coagulation as a risk factor has been studied extensively. In this review, we evaluated studies that investigated the association between fibrinolysis and thrombosis.

RECENT FINDINGS

There is some evidence for an association between impaired overall fibrinolytic activity and increased risk of venous or arterial thrombosis. Plasminogen levels were found not to be related to thrombosis. Plasma levels of tissue-type plasminogen activator were related to arterial thrombosis in a number of studies but not to venous thrombosis. Thrombin activatable fibrinolysis inhibitor levels appeared to be associated with venous thrombosis. Studies on the association between thrombin activatable fibrinolysis inhibitor or plasminogen activator inhibitor-1 and arterial thrombosis had conflicting results.

SUMMARY

Current evidence on an association between fibrinolysis and thrombosis is inconclusive. Although overall assays point to an association, not all individual factors have an association with thrombosis. Most importantly, plasminogen deficiency is not related to thrombosis, which suggests that the fibrinolytic system as a whole is unimportant in the occurrence of thrombosis. Certain components of the fibrinolytic system, however, appear to be involved in processes unrelated to fibrin degradation but related to other processes important in the development of thrombosis.

Molecular characterization of an Italian patient with plasminogen deficiency and ligneous conjunctivitis

Plasminogen deficiency is a rare disease characterized by ligneous conjunctivitis and infections. We observed a 3-year-old Italian boy presenting ligneous conjunctivitis and low plasma levels of plasminogen. Twenty-three different mutations on the PLG gene have been reported to date, but mutation analysis had been troublesome for the presence of highly homologous genes. The aim of the study was to identify the underlying mutation avoiding coamplification of unwanted genetic materials using a long polymerase chain reaction strategy, instead of the previously reported subcloning methods. By this simple strategy the complete sequence analysis of PLG gene was performed, and a previously reported missense homozygous mutation (K19E) was identified.

Hereditary thrombophilia

Thrombophilia can be defined as a predisposition to form clots inappropriately. Thrombotic events during infancy and childhood are increasingly recognized as a significant source of mortality and morbidity. The predisposition to form clots can arise from genetic factors, acquired changes in the clotting mechanism, or, more commonly, an interaction between genetic and acquired factors. Since the turn of the last century, there has been extensive research focusing on both the genetic and acquired causes of thrombophilia, with particular focus on clotting events in the venous circulation. This review describes clinically relevant aspects of genetic venous thrombophilia, which include well-established, lesser known, and suggested causes of inherited thrombophilias.

Platelet apheresis affects prothrombin time and plasminogen levels in healthy donors

There are few studies evaluating whether platelet apheresis has an effect on hemostasis parameters or not. The aim of this study was to define the effects of platelet apheresis on hemostasis screening tests and plasminogen levels. The study was performed on 40 healthy donors. We compared the values obtained before and after apheresis and observed that the prothombin time (PT) elongated, plasminogen levels decreased and the activated partial thromboplastin and thrombin times were not changed significantly. The differences were not high enough to cause any hemostasis problem. It can be hypothesized that platelet apheresis affects PT and plasminogen levels in healthy donors.

Reduced plasma fibrinolytic potential is a risk factor for venous thrombosis

The role of the fibrinolytic system in the development of deep vein thrombosis (DVT) is unclear. We determined the plasma fibrinolytic potential of patients enrolled in the Leiden Thrombophilia Study (LETS), a population-based case-control study on risk factors for DVT. Plasma fibrinolytic potential was determined in 421 patients and 469 control subjects by means of a tissue factor-induced and tissue-type plasminogen activator (tPA)-induced clot lysis assay. Using clot lysis times above the 70th, 80th, 90th, 95th, and 99th percentiles of the values found in control subjects as cut-off levels, we found a dose-dependent increase in risk for DVT in patients with hypofibrinolysis (odds ratios of 1.4, 1.6, 1.9, 2.1, and 2.2, respectively). This indicates a 2-fold increased risk of DVT in subjects with clot lysis times above the 90th percentile. The risk increase was not affected by age or sex (adjusted odds ratio for 90th percentile, 2.0), and after correction for all possible confounders (age, sex, and levels of procoagulant proteins shown to associate with clot lysis times in the control population), the risk estimate was marginally reduced (odds ratio, 1.6 for 90th percentile). Taken together, these results indicate that plasma hypofibrinolysis constitutes a risk factor for venous thrombosis, with a doubling of the risk at clot lysis times that are present in 10% of the population.

Poly-l-histidine downregulates fibrinolysis

The elevated level of histidine-rich glycoprotein was considered a risk factor of inherited thrombophilia. However, the mode of action remains largely unclear. In the current study, we employ poly-l-histidine (PLH) mimicking the histidine-rich region and determine whether PLH modulates urokinase (uPA)-dependent fibrinolysis. In an in vitro model, turbidity appearance and clearance monitored fibrin polymer formation and lysis, respectively. Fibrin polymer formed upon fibrinogen incubation with thrombin. In the presence of uPA or plasmin, fibrin polymer lysis took place in a dose-dependent manner as a function of time. We demonstrated that PLH significantly downregulated uPA-dependent fibrinolysis. PLH had no effect on plasminogen activation, as evidenced by no inhibitions on either uPA amidolytic activity or plasmin formation derived from its zymogen. Nor did PLH show any inhibition on plasmin amidolytic activity. PLH caused a profound delay of plasmin-dependent fibrinolysis upon pre-incubation of either plasmin or fibrinogen with PLH. The observations taken together suggest that the complex [plasmin-PLH-fibrin] formation significantly delayed plasmin-dependent fibrinolysis.

College of American Pathologists Consensus Conference XXXVI: Diagnostic Issues in Thrombophilia

OBJECTIVES

To review the state of the art relating to laboratory testing for thrombophilia, as reflected by the medical literature and the consensus opinion of recognized experts in the field, and to make recommendations regarding laboratory testing (whom to test, when to test, what tests to perform, rationale for testing, and other issues) in the assessment of thrombotic risk in individual patients and their family members.

DATA SOURCES

Review of the medical literature (primarily from the last 10 years) and the experience and opinions of experts in the field were used as data sources.

DATA EXTRACTION AND SYNTHESIS

Participating authors evaluated the medical literature and prepared manuscripts with specific proposed recommendations. Drafts of all of the manuscripts were prepared and circulated to every participant in the College of American Pathologists Conference XXXVI: Diagnostic Issues in Thrombophilia prior to the conference. Each of the conclusions and associated recommendations was then presented for discussion. Recommendations were accepted if a consensus of 70% or more of the 27 experts attending the conference was reached. The results of the discussion were then used to revise the manuscripts and recommendations into final form.

CONCLUSIONS

Consensus was reached on 179 recommendations, all of which are presented in articles in this issue of the Archives. Detailed discussion of the rationale for each of these recommendations is found in the text of the respective articles, along with citations to justify the level of evidence for the recommendations. This is an evolving area of research, and it is certain that further clinical studies will change many of the recommendations, cause some to be deleted, and add others in the future.