Ethnic differences in allelic associations of the interleukin-1 gene cluster in South African patients with inflammatory bowel disease (IBD) and in control individuals.

The allelic frequencies of TaqI, PstI, and variable number of tandem repeat (VNTR) polymorphisms of the IL-1beta, IL-1 receptor (IL-1Re), and IL-1 receptor antagonist (IL-1Ra) respectively, were investigated in black and white patients with inflammatory bowel diseases (IBD) and compared with control individuals. Plasma concentrations of IL-1beta and IL-1Ra were also determined in these individuals. The IL-1beta TaqI(-) allele was significantly more frequent in 50 white IBD patients (60%) compared with 47 white controls (17%), and 20 black patients (20%) (P=0.00001 and P=0.0001, respectively). The IL-1Re PstI(-) allele was significantly more frequent in 20 black patients (75%) compared with 50 white patients (44%) (P=0.0001). The frequency of the IL-1Ra 240-bp allele was lower in black (12%) compared with white controls (25%), (P=0.0151), and the 410-bp allele was more frequent in black (87%) compared with white (73%) controls (P=0.0096). Linkage disequilibrium was found in black individuals homozygous for the 410-bp allele of IL-1Ra, and the PstI(-) allele of IL-1Re (84%) (P=0.0032). There was a significantly increased level of IL-1Ra in black patients compared with white patients and black controls (P=0.0006 and P=0.0008, respectively). The population differences in allelic frequencies of the IL-1 gene cluster and IL-1Ra concentrations suggest that genetic and environmental factors play an important role in susceptibility to IBD.