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Glucocorticoids (GCs) are immunosuppressive drugs used for the acute treatment of patients with moderate to severe inflammatory bowel disease (IBD),1 but interindividual variability in the response to these agents is frequently observed.2 GCs diffuse freely into cells and bind to an intracellular receptor (hGR/NR3C1), so the sensitivity to these drugs may depend on the receptor number and affinity or on their availability to the receptors, and transport proteins (including P‐glycoprotein (Pgp) encoded by the MDR1/ABCB1 gene) can modify their intracellular concentration.3,4 Polymorphisms in the hGR and MDR1 genes have been described in different populations and may contribute to the variability in sensitivity to GCs observed in the clinical setting.3,4
A study was conducted to estimate the impact of genetic variations in hGR and MDR1 genes on the efficacy and individual response to GCs in young patients with IBD. Polymorphisms of the hGR gene (BclI and N363S which are related to GC hypersensitivity and ER22/23EK which is associated with relative resistance to GCs5) and the MDR1 gene (C3435T and G2677T which are associated with changes in Pgp expression and activity6) were studied in 119 young patients (58 female) with IBD (64 with Crohn's disease and 55 with ulcerative colitis) of mean (SD) age 11.7 (5.94) years at the onset of the disease and 100 consecutive healthy blood donors from the same geographical area using PCR‐RFLP.6,7,8 Patients were enrolled between July 2000 and March 2005 in the gastroenterology units of the Children's Hospitals of Trieste, Firenze and Genoa, Italy. The study included all consecutive patients with IBD who had been treated with GCs for at least 30 days (prednisone 1–2 mg/kg/day for 2–4 weeks and subsequent dose tapering by 5 mg/week to a dose of 20 mg and then by 2.5 mg/week below 20 mg) and had a minimum follow‐up period of 1 year. They were divided into two groups based on their response to GC treatment: GC‐dependence (n=45 patients) was defined by an initial response to prednisone with relapse on dose reduction, not allowing steroid discontinuation,9 and GC‐responsiveness (n=67 patients), equivalent to therapeutic success, was defined as GC withdrawal without the need for steroids for at least 1 year.10 Six patients (5.0%) initially had a partial response to GCs but steroid treatment was continued with the addition of azathioprine and aminosalicylates, so these patients were included in the study. Seven patients (5.9%) exhibited complete resistance to GCs and required colectomy; genetic analysis was also performed on this group and is reported in table 11.. These patients were not considered in the statistical analysis; however, their number was very low, similar to that described by other authors in children,11 and, in addition, they did not complete the scheduled observation period.
The genotype frequencies for all tested polymorphisms were consistent with the Hardy‐Weinberg equilibrium in both the study and control groups. A significantly higher frequency of BclI mutated genotype, associated with GC hypersensitivity, was observed in the GC‐responsive patients than in the GC‐dependent group (OR 0.15, 95% CI 0.03 to 0.68, p=0.0075/multiple testing corrected p=0.0375) or controls (OR 3.61, 95% CI 1.44 to 9.01, p=0.006/0.030). The significance was lost when the association was studied separately in patients with Crohn's disease (OR 0.23, 95% CI 0.045 to 1.13, p=0.10/0.5) and ulcerative colitis (OR 0.10, 95% CI 0.005 to 1.97, p=0.065/0.33) because of the small patient sample. No differences were observed for the other polymorphisms considered (table 11).). A significantly higher frequency of the BclI polymorphism was also evident in patients with Crohn's disease than in healthy volunteers (OR 2.93, 95% CI 1.14 to 7.54, p=0.03/0.06), confirming a previous observation in a smaller number of subjects (table 11).12
A logistic regression model, in which the response to GCs was the dependent variable and patients' age, sex, type of IBD and the considered genotypes were the independent variables, confirmed an independent significant association between the response to GCs and the variable BclI genotype (table 22).
This study shows that patients with mutated BclI genotype, which is associated with GC hypersensitivity, respond better to GC treatment and are less likely to need additional courses of steroid treatment. The mechanism of this effect is unclear at present. This polymorphism is intronic and not located in a coding, regulatory or splicing region of the hGR gene, but it may be linked to variations in the promoter region or 3′ untranslated region of the gene, or could act as a marker of other functionally important polymorphisms in the vicinity.13 Although this is the first study of the effects of hGR polymorphisms on sensitivity to GCs in IBD, previous work with the polymorphic hGR and MDR1 genotypes in other diseases has produced conflicting results, suggesting that the influence of these polymorphisms may vary depending on tissue type, disease and ethnicity.14
Given the high incidence of a suboptimal response to GCs in the treatment of IBD and the frequency of side effects, the identification of subjects who are likely to respond poorly to these agents would be very useful, and these patients should be treated earlier with steroid‐sparing drugs. The BclI polymorphism could therefore be a useful molecular marker to identify patients responsive to GC treatment.
This research was supported by grants from the Italian Ministry of University and Scientific Research (PRIN project 2005065797). SDI, GS and ID are recipients of a research fellowship from IRCCS Burlo Garofolo, Trieste.
Competing interests: None.