P53 germ line haplotypes associated with increased risk for colorectal cancer

Three p53 DNA polymorphisms (BstU I and Msp I restriction fragment length polymorphisms (RFLPs) in exon 4 and intron 6 respectively, and a 16 bp duplication in intron 3) and their haplotype combinations were studied in patients with colorectal cancer and compared with patients with ulcerative colitis and healthy controls. There were only minor differences between patients with ulcerative colitis and controls, the only significant difference was observed in the distribution of BstU I-Msp I haplotypes. When single polymorphisms were studied, a significantly lower frequency of the 16 bp duplication was found in patients with colorectal cancer. The protective effect of the 16 bp duplication was more pronounced in haplotype combinations with the BstU I A1 and Msp I A1 alleles, whereas these alleles in combination with the 16 bp A1 allele (no duplication) were associated with an increased risk for colorectal cancer. The genotypic combination BstU I 2-1, 16 bp 1-I, Msp I 2-1 was found in 8.4% of cases among patients with colorectal cancer and 0.5% of cases in the controls (odds ratio = 18.8). The extended haplotype responsible for the high cancer risk of this genotype appears to be BstU I A1-16 bp A1-Msp I A1. The results of this study indicate that the haplotype approach to the identification of p53 germ line alleles associated with increased susceptibility to cancer is far more powerful than the analysis of single polymorphisms, since the capacity to identify germ line alleles predisposing to cancer should increase with the number of polymorphic sites included in the analysis.