Susceptibility to refractory ulcerative colitis is associated with polymorphism in the hMLH1 mismatch repair gene

The hMLH1 gene lies in the linkage susceptibility region to inflammatory bowel disease (IBD) on 3p21. A single nucleotide polymorphism, 655A>G, in exon 8 of the gene causes an 1219V change in the MLH1 protein. To test whether hMLH1 may confer susceptibility to ulcerative colitis (UC), we investigated an association between the 655A>G polymorphism and the disease. DNA-based technologies were used to analyze the 655A>G polymorphism in 201 UC patients and 126 healthy ethnically matched controls. The comparison of the allelic frequencies of the 655A>G polymorphism in UC patients and healthy controls did not show significant differences. However, genotype frequencies at the hMLH1 655 position were found to be significantly different when patients with and without refractory UC were compared. This was mainly attributable to a higher level of homozygosity for the G allele in refractory UC patients. Almost 5 times as many (4.9 times) refractory UC patients carried the GG genotype compared with nonrefractory patients (P < 0.0001). The present study provides evidence that the hMLH1 gene is involved in genetic susceptibility to refractory UC. If confirmed by other studies, the GG genotype at position 655 of the hMLH1 gene may represent a useful predictive factor for the clinical management of UC patients.