Abstract

Defensins are endogenous antimicrobial peptides that protect the intestinal mucosa against bacterial invasion. It has been suggested that deficient defensin expression may underlie the chronic inflammation of Crohn disease (CD). The DNA copy number of the beta-defensin gene cluster on chromosome 8p23.1 is highly polymorphic within the healthy population, which suggests that the defective beta-defensin induction in colonic CD could be due to low beta-defensin–gene copy number. Here, we tested this hypothesis, using genomewide DNA copy number profiling by array-based comparative genomic hybridization and quantitative polymerase-chain-reaction analysis of the human beta-defensin 2 (HBD-2) gene. We showed that healthy individuals, as well as patients with ulcerative colitis, have a median of 4 (range 2–10) HBD-2 gene copies per genome. In a surgical cohort with ileal or colonic CD and in a second large cohort with inflammatory bowel diseases, those with ileal resections/disease exhibited a normal median HBD-2 copy number of 4, whereas those with colonic CD had a median of only 3 copies per genome (P=.008 for the surgical cohort; P=.032 for the second cohort). Overall, the copy number distribution in colonic CD was shifted to lower numbers compared with controls (P=.002 for both the surgical cohort and the cohort with inflammatory bowel diseases). Individuals with ≤3 copies have a significantly higher risk of developing colonic CD than did individuals with ⩾4 copies (odds ratio 3.06; 95% confidence interval 1.46–6.45). An HBD-2 gene copy number of 3; mean/median intensity 4) number of copies were about equal. Details of the copy number frequencies of all cohorts and subgroups are given in table 2.Table 2HBD-2 Gene Copy Number FrequenciesPercentage of Cohort with HBD-2 Gene Copy Number ofCohort2345678910Control: Cleveland5.015.045.025.05.05.0 Europe2.723.538.323.510.1.7.7.7Cleveland: Ileal1.736.735.020.06.7 Colonic12.060.016.08.04.0European: L15.023.343.321.71.75.0 L22.250.032.610.92.22.2 L38.532.235.615.35.13.4 UC5.333.333.314.79.32.71.3Note.—For the number of patients in these subgroups, see table 1. Open table in a new tab Note.— For the number of patients in these subgroups, see table 1. The U.S. patient cohort from the Cleveland Clinic consisted of 85 surgical patients with CD who had indications for ileal versus colonic resection. In patients with ileal resections (fig. 2B), the median number of copies was identical to that of the control group (4 copies); also, the frequency distribution of the three subgroups (with 4 gene copy numbers) was not significantly different from that of the control group. In contrast, the majority (72%) of patients with colonic resections had a copy number .05), with a majority in the group with 4 gene copies (fig. 3). The median was 4 copies in L1 and controls compared with 3 in L2 (P=.032 and P=.001, respectively [Mann-Whitney]). Analysis of variance and post hoc test identified a significant difference between L2 and controls only (P<.05). Colonic CD only (L2) was characterized by a shift to lower copy numbers, with the majority (52%) carrying <4 copies of HBD-2 (P=.002 vs. controls; P=.037 vs. L1 [Pearson χ2]). Individuals with ≤3 copies have a significantly higher risk of developing colonic CD than do individuals with ⩾4 copies (odds ratio 3.06; 95% CI 1.46–6.45). Patients with L3 showed an intermediate distribution pattern between controls and L2, and, although the median was the normal 4 copies, the shift in distribution was significant (P=.034 [Mann-Whitney]