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Crohn’s disease shows significant variability in incidence between different world populations. For example, Kurata and colleagues1 studied the annual incidence of Crohn’s disease in Caucasian, African, Asian, and Hispanic individuals, with an observed range from 43.6 per 100 000 population for Caucasian, 29.8 for African, 5.6 for Asian, and 4.1 for Hispanics. Recently, a genetic basis for Crohn’s disease has been described.2 The CARD15 gene (NOD2; MIM 605956) acts as a sensor for bacterial products. When functioning correctly, this would lead to activation of nuclear factor κB1.3 Sixty seven variations in the CARD15 genomic sequence have been reported.4,5 Of these 67, three variations (2104 C>T [R702W]; 2722 G>C [G908R]; 3020ins [1007fs]) have been consistently correlated with increased susceptibility to Crohn’s disease.4,6–8
Currently, these three variants have only been extensively assessed in patients of European, French Canadian, or American Caucasian descent. Using Pyrosequencing, we analysed all three variants in genomic DNA from 95 European (American Caucasian), 95 African (Ghanaian), and 53 Asian (Chinese) unrelated healthy volunteers. Frequencies for the R702W variant allele were 2% and 0% in European and African samples, respectively, 3% and 1% for G908R, and 3% and 0% for 1007fs (p<0.05 in all cases). None of the variants was observed in the Asian population, consistent with a recent study of Japanese patients with Crohn’s disease.9 The ethnic variation seen here could, in part, contribute to the variations in the frequency of Crohn’s disease in different world populations. Attention should be paid to the discovery of novel geographically selective variants before evaluating association with Crohn’s disease in non-European populations.
This work was supported in part by UO1 GM63340.