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-1 beta, IL-1 receptor (IL-1Re), and IL-1 re ceptor antagonist (IL-1Ra) respectively, were investigated in black and whi te patients with inflammatory bowel diseases (IBD) and compared with contro l individuals. Plasma concentrations of IL-1 beta and IL-1Ra were also dete rmined in these individuals. The IL-1 beta TaqI(-) allele was significantly more frequent in 50 white IBD patients (60%) compared with 47 white contro ls (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 pa tients (75%) compared with 50 white patients (44%) (P=0.0001). The frequenc y 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 blac k (87%) compared with white (73%) controls (P=0.0096). Linkage disequilibri um was found in black individuals homozygous for the 410-bp allele of IL-1R a, and the PsrI(-) allele of IL-1Re (84%) (P=0.0032). There was a significa ntly increased level of IL-1Ra in black patients compared with white patien ts 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 con centrations suggest that genetic and environmental factors play an importan t role in susceptibility to IBD.