A novel NOD2/CARD15 haplotype conferring risk for Crohn disease in Ashkenazi Jews

Abstract

Crohn disease (CD) exhibits a 2-4-fold increased frequency in Jews as compared with other ethnic/racial groups. Three coding variants of the NOD2/CARD15 have been reported as independent disease-predisposing mutations (DPMs), but these were found in only 30%-40% of patients with CD and could not account for all the linkage between CD and the IBD1 locus. The aim of the present study was to explore whether additional DPMs at the IBD1 locus exist in the high-risk Jewish group. Sixty-four Ashkenazi Jewish and 147 non-Jewish white families were studied. Six microsatellite markers spanning IBD1 were genotyped for linkage analysis in subgroups stratified on NOD2/CARD15 DPM status. SNPs in NOD2/CARD15 (R702W, G908R, 1007fs, and S268P) were then genotyped in family and independent case-control samples. On the basis of initial results, sequencing was done on NOD2/CARD15-translated regions in 12 Jewish individuals. Subsequently, a new NOD2/CARD15 variant was genotyped and analyzed. After excluding the influence of the three DPMs, significant linkage of IBD1 to CD in Jews remained with two peaks at D16S403 (mean allele sharing [MAS] = 0.70] and D16S411 (MAS = 0.59). Further, we observed an increased frequency of a haplotype carrying only the 268S variant in Jewish patients (OR = 3.13, P=.0023) but not in non-Jews, suggesting the existence of a Jewish-specific additional disease-predisposing factor on this haplotype. Sequencing of this haplotype revealed a new variant (IVS8+158; JW1). The 268S-JW1 combination exhibited a further increased risk (OR = 5.75, P=.0005) and the highest population-attributable risk (15.1%) for CD among reported DPMs in Jews. In Ashkenazi Jews, unrecognized population-specific predisposing factor(s) exist on the 268S-JW1 haplotype at the IBD1 locus. This factor may contribute to the higher risk for CD in Ashkenazi Jews as compared with non-Jews.

Figure 1

MAS in multiplex families with Crohn disease before and after stratification on presence or absence of three principal NOD2/CARD15 DPMs (702W, 908R, and 1007fs). Six microsatellite markers spanning NOD2/CARD15 locus on chromosome 16 were genotyped (from left to right, D16S403, D16S753, D16S409, D16S411, D16S419, and D16S408, respectively). Left panel, Jewish families. Right panel, non-Jewish families. Black circles represent the MAS from entire families (prestratification) in each ethnic group. White triangles represent the MASs in the families where there are no principal NOD2/CARD15 DPMs, and white squares represent the MASs in families with principal NOD2/CARD15 DPMs, after stratification.

Figure 2

NOD2/CARD15 polymorphisms observed in P268S-alone haplotypes in Ashkenazi Jewish patients with CD. CD1 and CD2 are homozygous patients with the P268S rare allele without known three DPMs (702W, 908R, and 1007fs). CD3–CD7 are heterozygous patients with 268S without the three DPMs. CD8–CD10 are patients and NC1 and NC2 are normal control individuals without any of four variants (268S and three DPMs). IVS = Intervening sequences; 1 = Common allele; 2 = Rare allele.

Figure 3

Haplotype structure of the five NOD2/CARD15 variants genotyped in this study. The letters in white squares indicate the variant (rare allele) of each SNP. The capital letters S, W, and R represent the amino acid variants serine, tryptophan, and arginine, respectively. The small letter t represents the nucleotide variant thymine at the JW1 SNP, and fs represents the frameshift mutation at the 1007fs SNP.

Figure 4

PAR of each CARD15-predisposing haplotype in Ashkenazi Jews and non-Jewish whites. The variant names in this figure represent each risk haplotype defined in table 3 and table 4.

Figure 5

The phylogenetic tree of five haplotypes generated by using CLUSTALW (a multiple alignments and tree-making program). This tree indicates the relationships between the CD-associated haplotypes in both Jewish and non-Jewish populations and a possible haplotype development consisting of five genotyped SNPs (P268S, R702W, G908R, 1007fs, and IVS8+158 [JW1]).