Early onset IBD: What's the difference

[Guest guest]



doi:10.1016/j.dld.2007.07.166 Copyright © 2007 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd.

Mini-Symposium

Early onset IBD: What's the difference

E.E.S. Nieuwenhuis1, a and J.C. Escher1, , a, aDepartment of Pediatric Gastroenterology, Sophia Children's Hospital-Erasmus Medical Center, Rotterdam, The Netherlands Received 23 July 2007; accepted 26 July 2007. Available online 7 November 2007.

Abstract

In this paper we describe an array of differences between paediatric and adult inflammatory bowel diseases. Specifically, patient specifics such as genetics, disease location, immune responses and drug responsiveness are addressed. Given the distinct disease phenotype in children, it seems warranted that early onset inflammatory bowel diseases will be denoted as a specific disease entity.

Keywords: Children; Disease phenotype; Epidemiology; Genetics; IBD; Immunology

Article Outline

1. Introduction 2. Epidemiology 3. Genetics 4. Early immune responses 5. Disease phenotype: location of disease 6. Disease phenotype: disease behaviour 7. Conclusion Conflict of interest statement References

1. Introduction

Inflammatory bowel diseases (IBD) result from aberrant mucosal immune responses to intestinal bacteria. Environmental triggers and genetic susceptibility are regarded as crucial contributors to the IBD pathogenesis. In children both the mucosal immune system and the intestinal microflora are still developing. Taken together it seems likely that paediatric IBD represents a specific group of patients with particular gene defects, phenotypic appearance, drug responsiveness and immune pathology. In this paper, we will focus on the differences between paediatric and adult IBD. 2. Epidemiology

About 10–15% of IBD patients are diagnosed before the age of 18 years [1]. Consistent with a peak around the age of 30 years, the incidence is 7 per 100,000 per year during puberty, and increases further during adolescence to 12 per 100,000 years in 20–29 year olds [2]. In children, most cohort studies show a predominance of incident cases of Crohn's disease (CD) over ulcerative colitis (UC) [3], with CD incidence clearly increasing over the past decade. By contrast, UC incidence is found to be stable in some studies [4], [5] and [6] but increasing in other cohorts [7], [8] and [9]. In most paediatric studies, the median age of onset of symptoms in UC is 12 years [2], [10] and [11], and the diagnostic delay is considerably shorter compared to CD. The clinical presentation of UC is often more severe in children compared to adults, which may be explained by the predominant finding of pancolitis (in 70–80% of children) already at the time of diagnosis [11] and [12]. In addition to the lower incidence number in children as compared to adults, and the predominance of CD over UC in children, another interesting difference exists between early onset and late onset IBD: a male preponderance is reported in paediatric CD [1], [11] and [13], while female preponderance is only seen among patients diagnosed in adolescence (13–19 years) [14], in accordance with the overall higher incidence of CD in females. 3. Genetics

IBD results from aberrant mucosal immune responses to environmental factors such as commensal bacteria. Based on the relatively short exposure time to environmental factors in children, genetic mutations that either enhance the susceptibility for or protect from these pathogenic responses are thought to play an increasing role in early onset disease. At least two reports support this hypothesis [15] and [16]. As such, it was recently shown that in comparison with adults, paediatric CD is associated with a higher frequency of mutation in the NOD2/CARD 15 gene in comparison to adult IBD patients. 4. Early immune responses

Traditionally, aberrant adaptive mucosal immune responses by (NK)T and B cells have been regarded as the main contributors to the pathogenesis of IBD [17]. Recent discoveries of defects in genes that mainly regulate interactions with the innate immune system have (re)focused the attention on the earliest phases of the immune response [18] and [19]. As such, both hypo- as well as hyper-responsiveness of these innate immune-cells have been put forward. For example, a loss of innate function in IBD has been established by showing a diminished expression of the antimicrobial defensins in Paneth cells (PC) of adult CD patients. Loss of function has also been described in another innate cell, the macrophage. Macrophages derived from CD patients with a mutation in NOD2/CARD-15 produced less of the pro-inflammatory chemo-attractant interleukine-8 on stimulation. These defects could therefore lead to suboptimal clearance and colonization control of intestinal bacteria resulting in chronic inflammation [20] and [21]. As loss of function mechanisms have not been identified yet in paediatric IBD patients, it is quite surprising that recent papers describe the opposite phenomenon, i.e. innate hyper-responsiveness. A group of paediatric CD patients showed enhanced epithelial chemokine production and responsiveness in comparison to adult CD patients. Whether this state of hyper-responsiveness will sustain into adulthood and would therefore represent a specific feature of early onset CD remains to be elucidated [22]. Of particular interest is the subset of patients with a very early onset IBD (onset before the age of 1 year). These patients presented with rectal bleeding and all seem to have colonic involvement. Intriguingly, there is evidence of an association with neonatal or early onset bacterial infections and use of antibiotics prior to the onset of IBD [23]. Taken together with the notion that both the intestinal microbiota as well as the mucosal immune system are still under development in children we speculate that the contributions of innate immune defects to the pathogenesis of IBD are inversely related to the age of disease onset. 5. Disease phenotype: location of disease

In the patients diagnosed with IBD at young age (before 5 years), anatomic distribution is clearly different with less isolated ileal disease in CD and more large bowel involvement in all types of IBD [24], [25] and [26]. The most commonly affected sites in CD are the terminal ileum (in 71% of patients at diagnosis) and right colon (71%) [11]. Upper gastrointestinal involvement is commonly seen in paediatric CD [22], [27] and [28], but this finding may be due to routine upper gastrointestinal endoscopy with biopsies at diagnosis (in addition to ileocolonoscopy) as dictated by consensus guidelines [29]. In ulcerative colitis, the disease is more widespread in children compared to adults at diagnosis: pancolitis in up to 90% [1], [11] and [12], and proctitis in only a minority of 4–13%. The more extensive localisation and the occurrence of rectal sparing in up to 30% of paediatric patients with UC [30] warrant a thorough complete diagnostic work-up in children with bloody diarrhoea. Evidence from the literature supporting the colonoscopy with ileal intubation (and multiple biopsies) is provided by retrospective cohort studies [30], [31] and [32]. In conclusion, sigmoidoscopy may be sufficient in adults, but certainly not in children or adolescents with suspected UC. Follow-up studies in paediatric IBD have shown that the extent of disease may change over time. As Crohn's disease progresses, anatomic distribution of macroscopic disease is probably similar in early and late onset disease [12], [14] and [33]. In ulcerative colitis, proximal extension of proctosigmoiditis is estimated to occur in 25% of young patients within 3 years of initial diagnosis and in 29–70% over the course of follow-up [33], [34] and [35]. 6. Disease phenotype: disease behaviour

In paediatric CD, simple inflammatory disease is described to be predominant (90%) at diagnosis [1]. However, complex stricturing and penetrating behaviour become more common over time. In a retrospective cohort of 224 patients with early onset CD with a mean follow-up of 12.2 years, the incidence of strictures (29%) and penetrating behaviour (46%) were similar to adults followed for the same period of time [14]. In paediatric CD, only 25% of patients present with the “classic triad†of abdominal pain, weight loss and diarrhoea [11]. Non-classical features such as lethargy or anorexia may be present, and abdominal pain is present in 72% but may be mild. A family history of IBD, growth failure (present in up to 65% of CD patients at diagnosis depending on its definition), pubertal delay or abnormalities on peri-anal examination should prompt further investigation leading to a diagnosis of CD. Extra intestinal manifestations (in 8.4%) and growth failure (in 3.3%) may predominate during years in absence of gastrointestinal symptoms [12]. Growth failure is three times less common in UC, compared to CD. Symptoms of blood loss (84%), diarrhoea (74%) and abdominal pain (62%) are often present at diagnosis in paediatric UC [11]. The above-mentioned difference in anatomic distribution is the most probable reason for the more severe clinical presentation in children, as compared to adults. Osteopenia may be present in children or adolescents at diagnosis [36] and [37] and although no long-term data are present and no proven treatment strategy has been published, screening and careful follow-up of bone health is warranted in children and adolescents with IBD [38]. Follow-up studies in paediatric IBD are now emerging and will yield important data on the clinical course of early onset disease. Whether the course of disease is different in children, adolescents and adults is unknown at present. Only a few studies however have compared patients with early onset and late-onset disease [14] and [33]. Langholz and co-workers reported on the course of clinical disease activity in patients with disease onset below and above age 14 [33]. In this retrospective study, no significant differences in disease activity at the time of diagnosis were found between young (≤14 years) patients and older (>14 years) patients. Disease activity was moderate to high in 74% of younger patients with UC, and in 83% of the young CD patients at diagnosis. After a year and continuing over a 10-year follow-up, about 50% of young CD patients were in clinical remission, none of the patients being treated with azathioprine at the time. Clinical remission was seen in 60–70% of young UC patients after a few years. A more recent study on the clinical course of CD in children and adolescents shows that the spectrum of disease severity during 5-years of follow-up has remained constant during the decades 1980–1988 and 1990–1999: one third has mild symptoms only, one third has occasional exacerbations returning to remission, while one third is chronically steroid-dependent or steroid-refractory [39]. The frequency of surgery in children with CD was reported to be 31.5% at 5-year follow-up, which is similar to the frequency in adults [3]. In this prospective study, the children who underwent surgery (mainly for ileal stenosis) were significantly younger (mean age 11 years) than those who did not (mean age 14.2 years). Retrospective data from the USA paediatric IBD consortium show a lower cumulative risk for surgery of 17% at 5 years and 28% at 10 years [40]. Recent data from the EPIMAD cohort, a population based cohort of IBD patients diagnosed from 1988 to 2002 in North-West France, show a cumulative risk of surgery in 10%, 22% and 36% of young (<17 years at diagnosis, n = 472) CD patients at 1 year, 3 years and 5 years after diagnosis [41]. The cumulative incidence of surgery ranges from 40% to 70% at 10 years from the time of diagnosis of CD in adults. In paediatric UC, 70% of patients enter remission within 3 months of initial diagnosis, irrespective of the severity at presentation (mild, moderate or severe) [42]. The severity of initial presentation correlated with long-term likelihood of colectomy: by 1 year, 9% and by 5 years, 26% of those presenting with moderate to severe disease required colectomy. Data from the EPIMAD cohort demonstrate a cumulative risk of surgery in 9%, 15% and 20% of UC patients (aged <17 years) at 1 year, 3 years and 5 years after diagnosis [43]. 7. Conclusion

In this paper we have described an array of differences between paediatric and adult IBD. Initiatives need to be taken in order to revise the nomenclature of IBD based on patient specifics such as genetics, disease location and drug responsiveness. In the light of these plans it seems warranted that early onset IBD will be denoted as a specific disease entity.

Practice points

• Genetic mutations are thought to play an increasing role in early onset IBD.

• Contributions of innate immune defects to the pathogenesis of IBD seem to be inversely related to the age of disease onset.

• Disease location is different in early onset IBD compared to adult IBD:

- more upper GI involvement and less isolated terminal ileum involvement in CD.

- more pancolitis and less proctitis in UC.

• Early onset IBD may have a more severe clinical presentation as compared to adults.

• Sigmoidoscopy may be sufficient in adults, but certainly not in children or adolescents with suspected UC.

Research agenda

• Further geno-, immuno- and pheno-typing of early onset IBD.

• Denotation of early onset IBD as a specific disease entity.

Conflict of interest statement

None declared.

References

[1] S. Kugathasan, R.H. Judd, R.G. Hoffmann, J. Heikenen, G. Telega and F. Khan et al., Epidemiologic and clinical characteristics of children with newly diagnosed inflammatory bowel disease in Wisconsin: a statewide population-based study, J Pediatr 143 (2003), pp. 525–531. Abstract | Full Text + Links | PDF (368 K) | View Record in Scopus | Cited By in Scopus (82) [2] V. Binder, Epidemiology of IBD during the twentieth century: an integrated view, Best Pract Res Clin Gastroenterol 18 (2004), pp. 463–479. Abstract | Full Text + Links | PDF (363 K) | View Record in Scopus | Cited By in Scopus (19) [3] K. Stordal, J. Jahnsen, B.S. Bentsen and B. Moum, Pediatric inflammatory bowel disease in southeastern Norway: a five-year follow-up study, Digestion 70 (2004), pp. 226–230. View Record in Scopus | Cited By in Scopus (3) [4] F.U. Urne and A. Paerregaard, Chronic inflammatory bowel disease in children. An epidemiological study from eastern Denmark 1998–2000, Ugeskr Laeger 164 (2002), pp. 5810–5814. View Record in Scopus | Cited By in Scopus (5) [5] C.H. Tsai, H.L. Chen, Y.H. Ni, H.Y. Hsu, Y.M. Jeng and C.J. Chang et al., Characteristics and trends in incidence of inflammatory bowel disease in Taiwanese children, J Formos Med Assoc 103 (2004), pp. 685–691. View Record in Scopus | Cited By in Scopus (5) [6] S. Auvin, F. Molinie, C. Gower-Rousseau, F. Brazier, V. Merle and B. Grandbastien et al., Incidence, clinical presentation and location at diagnosis of pediatric inflammatory bowel disease: a prospective population-based study in northern France (1988–1999), J Pediatr Gastroenterol Nutr 41 (2005), pp. 49–55. View Record in Scopus | Cited By in Scopus (10) [7] E. Armitage, H.E. Drummond, D.C. and S. Ghosh, Increasing incidence of both juvenile-onset Crohn's disease and ulcerative colitis in Scotland, Eur J Gastroenterol Hepatol 13 (2001), pp. 1439–1447. View Record in Scopus | Cited By in Scopus (43) [8] E. Lindberg, B. Lindquist, L. Holmquist and H. Hildebrand, Inflammatory bowel disease in children and adolescents in Sweden, 1984–1995, J Pediatr Gastroenterol Nutr 30 (2000), pp. 259–264. View Record in Scopus | Cited By in Scopus (62) [9] P. Turunen, K.L. Kolho, A. Auvinen, S. Iltanen, H. Huhtala and M. Ashorn, Incidence of inflammatory bowel disease in Finnish children, 1987–2003, Inflamm Bowel Dis 12 (2006), pp. 677–683. View Record in Scopus | Cited By in Scopus (4) [10] H.J. van der Zaag-Loonen, M. Casparie, J.A. Taminiau, J.C. Escher, R.R. Pereira and H.H. Derkx, The incidence of pediatric inflammatory bowel disease in the Netherlands: 1999–2001, J Pediatr Gastroenterol Nutr 38 (2004), pp. 302–307. View Record in Scopus | Cited By in Scopus (14) [11] A. Sawczenko and B.K. Sandhu, Presenting features of inflammatory bowel disease in Great Britain and Ireland, Arch Dis Child 88 (2003), pp. 995–1000. [12] A.M. Griffiths, Specificities of inflammatory bowel disease in childhood, Best Pract Res Clin Gastroenterol 18 (2004), pp. 509–523. Abstract | Full Text + Links | PDF (512 K) | View Record in Scopus | Cited By in Scopus (24) [13] C.N. Bernstein, J.F. Blanchard, P. Rawsthorne and A. Wajda, Epidemiology of Crohn's disease and ulcerative colitis in a central Canadian province: a population-based study, Am J Epidemiol 149 (1999), pp. 916–924. View Record in Scopus | Cited By in Scopus (139) [14] H.J. Freeman, Comparison of longstanding pediatric-onset and adult-onset Crohn's disease, J Pediatr Gastroenterol Nutr 39 (2004), pp. 183–186. View Record in Scopus | Cited By in Scopus (9) [15] L.W.R. de Ridder, G. Dijkstra, G. van der Steege, M.A. Benninga, I.M. Nolte and J.A.H.D. Taminiau et al., Genetic susceptibility has a more important role in pediatric-onset Crohn's disease than in adult-onset Crohn's disease, Inflamm Bowel Dis 13 (9) (2007), pp. 1083–1092. View Record in Scopus | Cited By in Scopus (1) [16] L. Sun, J. Roesler, A. Rosen-Wolff, U. Winkler, R. Koch and A. Thurigen et al., CARD15 genotype and phenotype analysis in 55 pediatric patients with Crohn disease from Saxony, Germany, J Pediatr Gastroenterol Nutr 37 (2003), pp. 492–497. View Record in Scopus | Cited By in Scopus (26) [17] D. Franchimont, G. Bouma, J. Galon, G.W. Wolkersdorfer, A. Haidan and G.P. Chrousos et al., Adrenal cortical activation in murine colitis, Gastroenterology 119 (2000), pp. 1560–1568. Abstract | PDF (576 K) | View Record in Scopus | Cited By in Scopus (20) [18] M. Rescigno and E.E. Nieuwenhuis, The role of altered microbial signaling via mutant NODs in intestinal inflammation, Curr Opin Gastroenterol 23 (2007), pp. 21–26. View Record in Scopus | Cited By in Scopus (1) [19] E.E. Nieuwenhuis and R.S. Blumberg, The role of the epithelial barrier in inflammatory bowel disease, Adv Exp Med Biol 579 (2006), pp. 108–116. [20] J. Wehkamp, N.H. Salzman, E. Porter, S. Nuding, M. Weichenthal and R.E. Petras et al., Reduced Paneth cell alpha-defensins in ileal Crohn's disease, Proc Natl Acad Sci U S A 102 (2005), pp. 18129–18134. View Record in Scopus | Cited By in Scopus (80) [21] D.J. Marks, M.W. Harbord, R. MacAllister, F.Z. Rahman, J. Young and B. Al-Lazikani et al., Defective acute inflammation in Crohn's disease: a clinical investigation, Lancet 367 (2006), pp. 668–678. Abstract | Full Text + Links | PDF (807 K) | View Record in Scopus | Cited By in Scopus (41) [22] G.M. Damen, J. Hol, L. de Ruiter, J. Bouquet, M. Sinaasappel and J. van der Woude et al., Chemokine production by buccal epithelium as a distinctive feature of pediatric Crohn disease, J Pediatr Gastroenterol Nutr 42 (2006), pp. 142–149. View Record in Scopus | Cited By in Scopus (1) [23] F.M. Ruemmele, M.G. El Khoury, C. Talbotec, C. Maurage, J.F. Mougenot and J. Schmitz et al., Characteristics of inflammatory bowel disease with onset during the first year of life, J Pediatr Gastroenterol Nutr 43 (2006), pp. 603–609. View Record in Scopus | Cited By in Scopus (2) [24] P. Mamula, G.W. Telega, J.E. Markowitz, K.A. Brown, P.A. Russo and D.A. Piccoli et al., Inflammatory bowel disease in children 5 years of age and younger, Am J Gastroenterol 97 (2002), pp. 2005–2010. Abstract | View Record in Scopus | Cited By in Scopus (40) [25] A. Sawczenko, B.K. Sandhu, R.F. Logan, H. , C.J. and S. Mian et al., Prospective survey of childhood inflammatory bowel disease in the British Isles, Lancet 357 (2001), pp. 1093–1094. Abstract | Full Text + Links | PDF (59 K) | View Record in Scopus | Cited By in Scopus (95) [26] M.B. Heyman, B.S. Kirschner, B.D. Gold, G. Ferry, R. Baldassano and S.A. Cohen et al., Children with early-onset inflammatory bowel disease (IBD): analysis of a pediatric IBD consortium registry, J Pediatr 146 (2005), pp. 35–40. Abstract | Full Text + Links | PDF (191 K) | View Record in Scopus | Cited By in Scopus (25) [27] J.M. Tobin, B. Sinha, P. Ramani, A.R. Saleh and M.S. , Upper gastrointestinal mucosal disease in pediatric Crohn disease and ulcerative colitis: a blinded, controlled study, J Pediatr Gastroenterol Nutr 32 (2001), pp. 443–448. View Record in Scopus | Cited By in Scopus (23) [28] P.S. Kundhal, M.O. Stormon, M. Zachos, J.N. Critch, E. Cutz and A.M. Griffiths, Gastral antral biopsy in the differentiation of pediatric colitides, Am J Gastroenterol 98 (2003), pp. 557–561. Abstract | View Record in Scopus | Cited By in Scopus (24) [29] IBD Working Group of the European Society for Paediatric Gastroenterology, Hepatology and Nutrition. Inflammatory bowel disease in children and adolescents: recommendations for diagnosis—the Porto criteria. J Pediatr Gastroenterol Nutr 2005;41:1–7. [30] J.N. Glickman, A. Bousvaros, F.A. Farraye, A. Zholudev, S. Friedman and H.H. Wang et al., Pediatric patients with untreated ulcerative colitis may present initially with unusual morphologic findings, Am J Surg Pathol 28 (2004), pp. 190–197. View Record in Scopus | Cited By in Scopus (17) [31] K.G.J. Washington, E. Montgomery, Y. Shyr, K.D. Crissinger, D.B. Polk and J. Barnard et al., Histopathology of ulcerative colitis in initial rectal biopsy in children, Am J Surg Pathol 26 (2002), pp. 1441–1449. View Record in Scopus | Cited By in Scopus (17) [32] J.C. Escher, K.F. ten, K. Lichtenbelt, I. Schornagel, H. Buller and B. Derkx et al., Value of rectosigmoidoscopy with biopsies for diagnosis of inflammatory bowel disease in children, Inflamm Bowel Dis 8 (2002), pp. 16–22. View Record in Scopus | Cited By in Scopus (10) [33] P. Munkholm, E. Langholz, O.H. Nielsen, S. Kreiner and V. Binder, Incidence and prevalence of Crohn's disease in the county of Copenhagen, 1962–87: a sixfold increase in incidence, Scand J Gastroenterol 27 (1992), pp. 609–614. View Record in Scopus | Cited By in Scopus (138) [34] J. Hyams, P. , T. Lerer, R.B. Colletti, A. Bousvaros and A. Leichtner et al., Clinical outcome of ulcerative proctitis in children, J Pediatr Gastroenterol Nutr 25 (1997), pp. 149–152. View Record in Scopus | Cited By in Scopus (8) [35] S.H. Mir-Madjlessi, W.M. Michener and R.G. Farmer, Course and prognosis of idiopathic ulcerative proctosigmoiditis in young patients, J Pediatr Gastroenterol Nutr 5 (1986), pp. 571–575. [36] R. Gokhale, M.J. Favus, T. Karrison, M.M. Sutton, B. Rich and B.S. Kirschner, Bone mineral density assessment in children with inflammatory bowel disease, Gastroenterology 114 (1998), pp. 902–911. Abstract | Full Text + Links | PDF (120 K) | View Record in Scopus | Cited By in Scopus (97) [37] E.J. Semeao, A.F. Jawad, N.O. Stouffer, B.S. Zemel, D.A. Piccoli and V.A. Stallings, Risk factors for low bone mineral density in children and young adults with Crohn's disease, J Pediatr 135 (1999), pp. 593–600. Abstract | Full Text + Links | PDF (50 K) | View Record in Scopus | Cited By in Scopus (63) [38] E. Hait, A. Bousvaros and R. Grand, Pediatric inflammatory bowel disease: what children can teach adults, Inflamm Bowel Dis 11 (2005), pp. 519–527. [39] P. Hofley, J. Roarty, G. McGinnity, A.M. Griffiths, M. Marcon and S. Kraft et al., Asymptomatic uveitis in children with chronic inflammatory bowel diseases, J Pediatr Gastroenterol Nutr 17 (1993), pp. 397–400. View Record in Scopus | Cited By in Scopus (13) [40] N. Gupta, S.A. Cohen, A.G. Bostrom, B.S. Kirschner, R.N. Baldassano and H.S. Winter et al., Risk factors for initial surgery in pediatric patients with Crohn's disease, Gastroenterology 130 (2006), pp. 1069–1077. Abstract | Full Text + Links | PDF (155 K) | View Record in Scopus | Cited By in Scopus (8) [41] G.B.M. Vernier-Massouille and C. Gower-Rousseau et al., Risk factors for initial surgery in pediatric patients with Crohn's disease (CD): a population-based cohort study (EPIMAD), J Pediatr Gastroenterol Nutr 44 (2007), p. e253. [42] J.S. Hyams, P. , K. Grancher, T. Lerer, C.J. ich and J. Markowitz, Clinical outcome of ulcerative colitis in children, J Pediatr 129 (1996), pp. 81–88. Abstract | Full Text + Links | PDF (712 K) | View Record in Scopus | Cited By in Scopus (40) [43] D. Turck, C. Gower-Rousseau, G. Vernier-Massouille, E. Tilloy, M. Baldé and F. Brazier et al., Natural history of pediatric ulcerative colitis (UC): a population-based cohort study (EPIMAD), J Pediatr Gastroenterol Nutr 44 (2007), p. e249.

Corresponding author at: Department of Paediatric Gastroenterology, Erasmus Medical Center-Sophia Children's Hospital, POB 2060, 3000 CB Rotterdam, The Netherlands. Tel.: +31 10 4637093/6049; fax: +31 10 4636811.1 Both authors contributed equally to this work.

Digestive and Liver Disease Volume 40, Issue 1, January 2008, Pages 12-15