Hemostasis in Crohn's disease: low factor XIII levels in active disease

Factor XIII-A in Diseases: Role Beyond Blood Coagulation

Multidisciplinary research from the last few decades has revealed that Factor XIII subunit A (FXIII-A) is not only involved in blood coagulation, but may have roles in various diseases. Here, we aim to summarize data from studies involving patients with mutations in the F13A1 gene, performed in FXIII-A knock-out mice models, clinical and histological studies assessing correlations between diseases severity and FXIII-A levels, as well as from in vitro experiments. By providing a complex overview on its possible role in wound healing, chronic inflammatory bowel diseases, athe-rosclerosis, rheumatoid arthritis, chronic inflammatory lung diseases, chronic rhinosinusitis, solid tumors, hematological malignancies, and obesity, we also demonstrate how the field evolved from using FXIII-A as a marker to accept and understand its active role in inflammatory and malignant diseases.

Factor-XIII activity in patients with mild to moderate ulcerative colitis and active bleeding: a prospective observational study

OBJECTIVE

Coagulation factor XIII plays a key role in fibrin clot stabilization and epithelial healing. Under chronic inflammatory conditions involving bleeding and an activation of the coagulation cascade, the FXIIIa inversely correlate with disease activity. We assumed that FXIIIa could be a predictor of severity in patients with ulcerative colitis (UC). Here, we evaluated the course of plasma activity of FXIIIa in 49 patients with mild to moderate UC and active rectal bleeding. Patients with a partial Mayo bleeding subscore > 2 were eligible to participate in our prospective observational study in an outpatient setting. FXIIIa was investigated during acute flare conditions, after bleeding had stopped and later on in quiescent UC.

RESULTS

Plasma activity of FXIIIa did not show any significant differences during the UC course. FXIIIa was measured below normal range < 70% in only 8 patients during the flare and increased to normal values during follow-up in 7 of these patients. Low FXIIIa during the flare was not associated with an increased bleeding activity. In patients with a mild to moderate UC flare and prolonged bleeding, FXIIIa activity is neither predictive of UC severity nor of any bleeding activity in an outpatient setting. Trial registration This non interventional, non pharmacological prospective study was not obligated to receive a unique identifying number. This trial is registered with the Ethics Committee of the State Medical Chamber of Saxony, Dresden, Germany (Clinical Trials Registry number EK-BR-03/14-1).

Tissue-regenerating functions of coagulation factor XIII

The protransglutaminase factor XIII (FXIII) has recently attracted attention within the field of tissue regeneration, as it has been found that FXIII significantly influences wound healing by exerting a multitude of functions. It supports hemostasis by enhancing platelet adhesion to damaged endothelium, and by its cross-linking activity it stabilizes the formed fibrin clot. Furthermore, FXIII limits bacterial dissemination from the wound and incorporates macromolecules of importance for cellular infiltration, supporting cell migration and survival. FXIII-mediated complex formation of the vascular endothelial growth factor receptor 2 and αV β3 integrin is important for angiogenesis, supporting the formation of granulation tissue. Chronic inflammatory conditions involving bleeding and activation of the coagulation cascade have been shown to lead to reduced FXIII levels in plasma. Of particular importance for this review is the fact that patients suffering from inflammatory bowel disease (IBD) have reduced FXIII antigen levels and activity. Furthermore, these patients show impaired mucosal healing, which supports the inflammatory state of the disease. This review summarizes the role of FXIII in the healing of wounds, and briefly summarizes the previous use of FXIII in clinical settings. Moreover, it addresses the potential role for FXIII as a therapeutic agent in the healing of persistent wounds during chronic conditions, with an emphasis on IBD.

The usefulness of factor XIII levels in Crohn's disease

BACKGROUND AND AIMS

The assessment of inflammatory activity in Crohn's disease (CD) is challenging, and no specific laboratory marker is currently available. Several studies have reported decreased serum factor XIII levels in CD patients as a function of disease activity. We aimed to determine whether the factor XIII level could be a marker for the evolution of CD.

METHODS

In this prospective, single-centre trial, 129 patients were included and categorised into two groups: functional bowel disorders (FBDs, n=42) and CD (n=86). The CD group was divided into two subgroups depending on disease activity, as defined by the Crohn's Disease Activity Index score: active disease (CDa, n=41) and disease remission (CDb, n=45). The factor XIII levels were evaluated for each patient. Serial factor XIII levels were evaluated in the patients within the CDa subgroup.

RESULTS

The factor XIII levels were significantly different between the FBD (117.69%) and CD (101.89%) groups (p=0.009) but there was no significant difference between the CDa and CDb subgroups (99.04% vs 104.65%, p>0.05), and the levels did not vary during follow-up for the patients in the CDa subgroup. By multivariate analysis, factor XIII levels did not correlate with the time course of disease evolution, CRP, serum fibrin levels, platelet count, disease distribution within the bowel, or the presence of a fistulising form of CD.

CONCLUSIONS

Our results confirm that factor XIII levels are decreased in CD patients but cannot be recommended as a marker for the disease activity.

Biomarker discovery for inflammatory bowel disease, using proteomic serum profiling

Crohn's disease and ulcerative colitis known as inflammatory bowel diseases (IBD) are chronic immuno-inflammatory pathologies of the gastrointestinal tract. These diseases are multifactorial, polygenic and of unknown etiology. Clinical presentation is non-specific and diagnosis is based on clinical, endoscopic, radiological and histological criteria. Novel markers are needed to improve early diagnosis and classification of these pathologies. We performed a study with 120 serum samples collected from patients classified in 4 groups (30 Crohn, 30 ulcerative colitis, 30 inflammatory controls and 30 healthy controls) according to accredited criteria. We compared protein sera profiles obtained with a Surface Enhanced Laser Desorption Ionization-Time of Flight-Mass Spectrometer (SELDI-TOF-MS). Data analysis with univariate process and a multivariate statistical method based on multiple decision trees algorithms allowed us to select some potential biomarkers. Four of them were identified by mass spectrometry and antibody based methods. Multivariate analysis generated models that could classify samples with good sensitivity and specificity (minimum 80%) discriminating groups of patients. This analysis was used as a tool to classify peaks according to differences in level on spectra through the four categories of patients. Four biomarkers showing important diagnostic value were purified, identified (PF4, MRP8, FIBA and Hpalpha2) and two of these: PF4 and Hpalpha2 were detected in sera by classical methods. SELDI-TOF-MS technology and use of the multiple decision trees method led to protein biomarker patterns analysis and allowed the selection of potential individual biomarkers. Their downstream identification may reveal to be helpful for IBD classification and etiology understanding.

Clinical significance of measuring blood coagulation factor XIIIA regularly and continuously in patients with Crohn's disease

BACKGROUND

The aim of the present paper was to determine the mechanism by which the level of coagulation factor XIIIA declines during the active phase of Crohn's disease.

METHODS

The relationship between the activity of Crohn's disease and factor XIIIA was observed in 31 patients with Crohn's disease prospectively. The relationship between factor XIIIA and thrombin-antithrombin III complex (TAT), factor XIIIA expressed on the surface of peripheral monocytes, was also evaluated.

RESULTS

During the first year, there were 11 patients with Crohn's disease in the active phase and 20 patients who remained in remission. The average of the lowest level of factor XIIIA among the patients in the active phase was 60.1%. The average of the lowest level of factor XIIIA in patients who remained in remission was 78.1% (P = 0.049). Among the 20 patients who remained in remission for 1 year, eight patients had factor XIIIA levels below 70%. Six of them required surgical enterectomies, on average 2 years and 1 month later. However, none of the 12 patients who remained in remission for 1 year and who never had factor XIIIA levels <70% had a surgical enterectomy during follow up of 4 years and 6 months (P = 0.002). The decline of factor XIIIA was not due to increased consumption secondary to blood coagulation (TAT), nor was it due to a decline in the function of monocytes that produce factor XIIIA.

CONCLUSION

Factor XIIIA declines during the active phase of Crohn's disease because it might be consumed in the repair of injured tissue.

Coagulation factor XIII and markers of thrombin generation and fibrinolysis in patients with inflammatory bowel disease

OBJECTIVE

To relate factor XIII levels and other prothrombotic markers to inflammatory bowel disease and investigate the frequency of valine34leucine and its effect on factor XIII cross-linking activity in patients with inflammatory bowel disease.

DESIGN

Fifty patients with active inflammatory bowel disease but no venous thromboembolism (32 with ulcerative colitis, 18 with Crohn's disease), 50 patients with inactive inflammatory bowel disease but no venous thromboembolism (32 with ulcerative colitis, 18 with Crohn's disease), two age- and gender-matched healthy control groups of 100 subjects each were recruited. To further explore the relationship between valine34leucine and inflammatory bowel disease, 21 patients with the disease (13 with ulcerative colitis and eight with Crohn's disease) and venous thromoembolism (male to female ratio = 7 : 14, median age 59.5 years (range, 19-80 years)) were recruited. Two hundred and fifteen control subjects (M : F = 121 : 94, median age 62 years (28-74 years)), with venous thromboembolism (119 with deep venous thrombosis, and 96 with pulmonary embolism) were drawn from the same geographical area as the patients.

METHODS

Factor XIII A, B-subunit antigen and A2B2 tetramer levels were measured using an in-house sandwich enzyme-linked immunoassay method.

RESULTS

Factor XIII A2B2 tetramer and the A-subunit were significantly decreased in patients with active inflammatory bowel disease compared with controls (59% vs 95%, P < 0.0001 and 75% vs 102%, P < 0.0001, respectively), but not between the inactive inflammatory bowel disease group and controls. The D-dimer and prothrombin 1+2 fragment levels in patients with active inflammatory bowel disease were raised compared with controls (178 (152) vs 109 (84), P = 0.0007 and 82 (43) vs 55 (28), P = 0.0001, respectively). The factor XIII B-subunit and factor XIII cross-linking activity were not significantly different between patients with active or inactive inflammatory bowel disease and controls. There was no significant difference in genotype distribution in inflammatory bowel disease patients with or without venous thromboembolism and respective control subjects. Levels of tissue plasminogen activator antigen were significantly increased in patients with active inflammatory bowel disease when compared to inactive inflammatory bowel disease and controls (8.9 (3.7) vs 6.7 (3.4) vs 6.9 (3.4), P < 0.001).

CONCLUSIONS

Active inflammatory bowel disease is associated with activation of coagulation. Factor XIII A and A2B2 tetramer levels were markedly decreased in active inflammatory bowel disease. Variations in the level of factor XIII in patients with inflammatory bowel disease could be multifactorial and in part may result from the increased formation of microthrombi and accelerated turnover of the factor XIII. We found no evidence of association of factor XIII valine34leucine polymorphism and inflammatory bowel disease.

Acute lower gastrointestinal bleeding in Crohn's disease: characteristics of a unique series of 34 patients. Belgian IBD Research Group

OBJECTIVE

Acute lower gastrointestinal bleeding is a rare complication of Crohn's disease, which represents a diagnostic and therapeutic challenge. The aim of this study was to define epidemiological characteristics and therapeutic options of hemorrhagic forms of Crohn's disease.

METHODS

Thirty-four cases of hemorrhagic forms of Crohn's disease were studied retrospectively. Acute lower gastrointestinal hemorrhage was defined as acute rectal bleeding originating in diseased bowel and requiring a transfusion of at least 2 units of red blood cells within 24 h. Upper gastrointestinal tract hemorrhage or anal lesions and postoperative bleeding were excluded.

RESULTS

Mean age at time of hemorrhage was 34.2 +/- 14 yr. Mean duration of disease before the hemorrhage was 5.6 +/- 6 yr. The hemorrhage occurred during a flare up of the disease in 35% of cases. The hemorrhage revealed Crohn's disease in 23.5% of cases. The hemorrhage was more frequent in colonic disease (85%) than in isolated small bowel disease (15%) (p < 0.0001). The origin of bleeding was identified in 65% of cases, by colonoscopy (60%), by angiography (3 patients), or at surgery (1 patient). The bleeding lesion was an ulcer in 95% of cases, most often in the left colon. The treatment was surgical in 20.5% (colectomy in 36%), endoscopical (7 patients, including 5 successes), or medical. Hemorrhage recurred in 12 patients (35%) within a mean time of 3 yr (4 days-8 yr), requiring surgery in 3 cases. No death was observed.

CONCLUSIONS

This study performed in a series characterized by a nonsurgical recruitment, the largest to date, shows that hemorrhagic forms of Crohn's disease may reveal disease in 23.5%, occurs in quiescent Crohn's disease in two-thirds of cases. Given the potential efficacy of endoscopical or medical treatment, as well as the absence of mortality, a conservative approach may be suggested as first-line therapy in the majority of patients.

Factor XIII modulates intestinal epithelial wound healing in vitro

BACKGROUND

An acquired deficiency of blood coagulation factor XIII has been proposed to cause an impairment of intestinal wound healing and hemostasis in patients with inflammatory bowel diseases. Substitution of factor XIII seems to result in a rapid improvement of intestinal wound healing. Our aim was therefore to characterize the role of factor XIII in the modulation of intestinal wound healing in vitro.

METHODS

Factor XIII was added to subconfluent cultures of two non-transformed small-intestinal epithelial cell lines (IEC-6, IEC-18) and three human colon cancer-derived epithelial cell lines (T84, CaCo-2, HT-29) with subsequent assessment of cell proliferation with a colorimetric 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenylformazan (MTT) assay. The effects on epithelial cell migration in vitro were assessed with an in vitro wounding model of confluent IEC-6 cell monolayers.

RESULTS

Factor XIII caused a modest inhibition of proliferation of IEC-6 and IEC-18 cells. However, factor XIII significantly stimulated proliferation of T84, CaCo-2. and HT-29 cell lines. In addition, thrombin-activated factor Xill promoted intestinal epithelial cell restitution in vitro on average 2.5-fold. The modulatory effects of factor XIII could not be significantly blocked by anti-transforming growth factor beta (TGFbeta).

CONCLUSIONS

Factor XIII may promote intestinal epithelial wound healing by enhancement of epithelial cell restitution through a TGFbeta-independent pathway. This may explain previously described beneficial effects of factor XIII in the treatment of active ulcerative colitis.

Genotype/Phenotype Correlations for Coagulation Factor XIII: Specific Normal Polymorphisms Are Associated With High or Low Factor XIII Specific Activity

Factor XIII is a transglutaminase essential for normal hemostasis. We have studied the plasma FXIII levels and FXIII activity in 71 individuals and found these to be normally distributed. FXIII specific activity is also normally distributed. However, we show that FXIII activity is not directly dependent on FXIII levels, and individuals with low FXIII levels may have high FXIII activity and vice versa. We have determined the FXIIIA genotype in these individuals to assess whether the variation observed in FXIII specific activity is dependent on specific polymorphisms in the FXIIIA gene. Our data show that the Leu34 and Leu564 variants give rise to increased FXIII specific activity, while the Phe204 variant results in lower FXIII specific activity. We also report preliminary evidence that the Phe204 polymorphism may be associated with recurrent miscarriage. Overall, we have identified 23 unique FXIIIA genotypes. Certain specific FXIIIA genotypes consistently give rise to high, low, or median FXIII specific activity levels, while others appear to have little or no consistent influence on the FXIII phenotype. These genotype to phenotype relationships are discussed in light of the growing interest in the role of FXIII in clinical problems involving an increased thrombotic tendency.

Genotype/Phenotype Correlations for Coagulation Factor XIII: Specific Normal Polymorphisms Are Associated With High or Low Factor XIII Specific Activity

Factor XIII is a transglutaminase essential for normal hemostasis. We have studied the plasma FXIII levels and FXIII activity in 71 individuals and found these to be normally distributed. FXIII specific activity is also normally distributed. However, we show that FXIII activity is not directly dependent on FXIII levels, and individuals with low FXIII levels may have high FXIII activity and vice versa. We have determined the FXIIIA genotype in these individuals to assess whether the variation observed in FXIII specific activity is dependent on specific polymorphisms in the FXIIIA gene. Our data show that the Leu34 and Leu564 variants give rise to increased FXIII specific activity, while the Phe204 variant results in lower FXIII specific activity. We also report preliminary evidence that the Phe204 polymorphism may be associated with recurrent miscarriage. Overall, we have identified 23 unique FXIIIA genotypes. Certain specific FXIIIA genotypes consistently give rise to high, low, or median FXIII specific activity levels, while others appear to have little or no consistent influence on the FXIII phenotype. These genotype to phenotype relationships are discussed in light of the growing interest in the role of FXIII in clinical problems involving an increased thrombotic tendency.

Arg506Gln factor V mutation and Val34Leu factor XIII polymorphism in Finnish patients with inflammatory bowel disease

BACKGROUND

Earlier studies have indicated that inflammatory bowel disease (IBD), including Crohn's disease (CD) and ulcerative colitis (UC), is associated with thromboembolic complications, whereas inherited disorders of coagulation occur less often than expected in IBD patients. The point mutation Arg506Gln of factor V (Factor V Leiden), resulting in resistance to activated protein C, is the commonest inherited form of thrombophilia. Alterations in circulating levels of factor XIII (FXIII) have been reported among IBD patients. We investigated whether Factor V Leiden or inherited Val34Leu polymorphism of FXIII would associate with IBD or its clinical outcome.

METHODS

Factor V Leiden mutation and FXIII Val34Leu polymorphism were assayed in 328 unrelated Finnish patients with UC and 235 patients with CD by solid-phase minisequencing techniques. The control groups comprised 142 apparently healthy Finnish subjects and 120 Finnish blood donors.

RESULTS

The frequency of Factor V Leiden mutation among IBD patients (4.5%) was not significantly different from that in subjects living in the same area (2.1%). No significant differences could be observed in the FXIII Val34Leu polymorphism allele frequencies between patients and controls. Clinical features of IBD, including the disease extent, requirement for immunosuppressive drugs, and occurrence of complications, seemed to be independent of these two clotting factor variants analyzed.

CONCLUSIONS

Our data do not support an aetiologic or disease-modifying role for the factor V mutation or factor XIII Val34Leu polymorphism in IBD.

Hemostatic abnormalities in inflammatory bowel disease

Patients affected by inflammatory bowel disease (IBD) frequently suffer from thromboembolic events. Aims of this study were to investigate hemostatic system and the presence of antiphospholipid antibodies (aPL) in IBD patients. Forty-one patients affected by Crohn's disease (CD) and 19 by ulcerative colitis (UC) were studied, compared to 40 healthy control subjects. Platelet count (PLT), PT, aPTT, fibrinogen (Fib), prothrombin fragment F1+2, antithrombin (AT), protein C (PC), protein S (PS), factor XIII (FXIII), plasminogen (PLG), plasminogen activator inhibitor (PA1), spontaneous platelet aggregation in platelet-rich plasma (PRP-SPA) and in whole blood (WB-SPA), and antiphospholipid antibodies (aPL) were evaluated. PLT, Fib, F1+2 and WB-SPA were significantly increased in IBD patients (p at least <0.05) both in active and inactive phases; aPL positivity was more frequent (p<0.05) and FXIII was significantly decreased (p<0.05) in comparison to control subjects. The thrombophilic state of IBD patients is not related to the degree of activity of the disease or to previous thrombotic events; aPL express the immunological alterations connected with IBD and are not the main cause of thrombotic events.

Fibrinolytic split products, fibrinolysis, and factor XIII activity in inflammatory bowel disease

BACKGROUND

Factor XIII (F XIII), the last coagulation factor in the clotting cascade, plays a role in mucosal repair. Beneficial effects of F XIII supplementation in severe ulcerative colitis (UC) have been observed. The aim of this study was to relate plasma F XIII activity to the severity of inflammatory bowel disease (IBD).

METHODS

A transversional and, in part, longitudinal study of F XIII activity and related clotting products was performed in 39 patients with UC, 31 patients with Crohn's disease (CD), and 20 controls. Disease activity was assessed with a combined activity score in UC and with the Dutch Activity Index in CD.

RESULTS

F XIII activity was decreased in active UC (p < 0.05) and active CD (p < 0.05) and was inversely correlated with severity in both UC (r = -0.30) and CD (r = -0.46). In six patients with UC (15%) and six patients with CD (19%) F XIII activity was below the lower range of normal. In these patients apparent rectal bleeding was only found in severe UC. Hyperfibrinolysis was indicated by elevated levels of D-dimer (p < 0.001) notwithstanding increased concentrations of alpha-2 antiplasmin (p < 0.05).

CONCLUSIONS

In active IBD we found decreased plasma F XIII activity and hyperfibrinolysis. Decreased F XIII activity was not associated with apparent rectal bleeding in IBD.

Coagulation factor XIII in plasma of patients with benign and malignant gynaecological tumours

Fibrinogen and factor XIII were measured in sixty-four women with recently detected gynaecological tumours. Twenty-six of these tumours were benign and 32 were malignant: of the last group, nine patients had metastases. No patient showed clinical signs of bleeding or thrombosis. A reference group consisted of 31 age-matched healthy women. For fibrinogen, no significant deviation between the patient groups and the control group was found. The median values of factor XIII were higher in the benign tumour group than in the control group. In patients with a gynaecological tumour and metastases, factor XIII was significantly lower than in the non-metastasized malignancy group or in the benign tumour group.

Factor XIIIA subunit and Crohn's disease

Factor XIIIA is the active subunit of plasma factor XIII that is responsible for cross linking fibrin into a stable clot. Sixteen patients with Crohn's disease were studied prospectively from relapse (Crohn's disease activity index > 150) into remission. Plasma factor XIIIA concentrations were significantly lower in active disease (median 63 (95% CI 46-72) U/dl) than remission (median 90 (95% CI 60-112) U/dl; p = 0.002). Plasma factor XIIIA concentrations correlated positively with the activity index (p = 0.005) and platelet count (p = 0.003), and negatively with serum albumin (p = 0.006). In five patients with persistent aggressive disease, the factor XIIIA concentration remained below the lower range of normal despite apparent clinical improvement in response to medical treatment. Tissues from three patients who underwent surgical resection during the study were immunostained for factor XIIIA. Gut mucosal and submucosal macrophages stained strongly for factor XIIIA. In one patient, capillary thrombi near superficial mucosal erosions immunostained for factor XIIIA in macroscopically normal mucosa. Similar changes were identified in more severely inflamed sections of intestine from the other two patients. The demonstration of significantly low plasma factor XIIIA concentrations in active Crohn's disease, and the immunostaining of factor XIIIA in capillary thrombi in the bowel wall, suggest that activation of coagulation may be involved in the pathogenesis of Crohn's disease. The plasma factor XIIIA concentration may prove a useful laboratory marker of disease activity.

Development and evaluation of ELISAs for factor XIIIA and XIIIB subunits in plasma

Severe, congenital deficiency of factor XIII is extremely rare. However, a moderate reduction in the plasma level of the functional subunit (factor XIIIA) and also to a lesser extent of the carrier subunit (factor XIIIB), and a decrease in the XIIIA:B subunit ratio, have recently been reported in patients with the inflammatory bowel disorder Crohn's disease, particularly during clinical relapse. In order to accurately monitor patients, sensitive, reliable assays for the two subunits of factor XIII are required. We report here the development and validation of ELISAs for these components. The assays are identical except in respect of the specificity of the polyclonal antiserum used as starting material, both of which are commercially available. The antisera are purified by n-octanoic acid precipitation and portions of these purified immunoglobulins are used as coating antibodies. The remaining portions are biotinylated and used with streptavidin and horse-radish peroxidase as tracer antibodies. A normal range (n = 24) was established for factor XIIIA (mean 95 range 60-130 U/dl) and for factor XIIIB (mean 99 range 60-130 U/dl). There were no significant differences between the ELISA and electroimmunodiffusion assays either for factor XIIIA (means +/- 1 standard deviation 95 +/- 15.9 and 89 +/- 22.7 respectively) or for factor XIIIB (99 +/- 18.3 and 106 +/- 23.4 respectively). These assays have been in routine use for six months, during which time two further antisera purifications and biotinylations have been carried out without significant problems of reproducibility or stability.

Pathogenesis of Crohn's disease: multifocal gastrointestinal infarction

In a prospective study, specimens of resected small and large intestine from fifteen patients with Crohn's disease were prepared by heparin-saline vascular perfusion, followed by either resin casting of the mesenteric vascular supply and tissue maceration or glutaraldehyde perfusion-fixation, resin casting, and tissue clearance. The specimens were examined by macrophotography, histopathology, and either scanning or transmission electronmicroscopy. A pathogenetic sequence of events in Crohn's disease was seen--vascular injury, focal arteritis, fibrin deposition, arterial occlusion mainly at the level of the muscularis propria, followed by tissue infarction or neovascularisation. These features were confined to segments of intestine affected by Crohn's disease and did not occur in normal bowel. The findings suggest that Crohn's disease is mediated by multifocal gastrointestinal infarction. This pathogenetic process is compatible with many of the clinical features of Crohn's disease, and its recognition has important implications for the identification of the primary cause of the illness and advances in clinical management.