Snps In The D-loop Region Of Mitochondrial DNA In Patients With Ibs

Background and Objective: Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal diseases (FGID), of which the pathogenesis remains unclear. It has been noted that FGID may be related with mitochondrial DNA single nucleotide polymorphism (SNP), therefore more attention has been paid to the association between IBS and mitochondrial DNA. D-loop region, especially hypervariable region ? and ?, became the "hot spot" of mitochondrial genome regarding mtDNA SNP. Researchers have found that SNPs of D-loop region play important roles in the occurrence and prognosis of various diseases such as tumors,infertility, ulcerative colitis and so on. But there is few reports concerning the effects of mtDNA SNPs on IBS. We divided patients with IBS into two groups: IBS with diarrhea (IBS-D) and IBS with constipation (IBS-C). We aim to find specific SNPs in mitochondrial DNA D-loop region in IBS.Methods: 40 cases were included in this study, of which 20 with IBS-D, 10 with IBS-C (who fulfilled with Rome ? criteria for IBS) and 10 as control group.Biopsies were obtained from the colon during the colonoscopy. Mitochondrial DNA D-loop region was sequenced and compared with standard mtDNA sequence(NC-012920) and checked in MITOMAP (www.mitomap.org).Results: 1. There are no significant difference regarding sex, age and BMI between IBS and control. 2. We have found a total of 108 SNPs in three groups, of which the major type of variation is base replacement (92.6%). SNPs mainly occur in hypervariable region ( ?, ? ) and no significant difference is found among three groups in this region (P=0.23). 17 SNPs occur in all groups, and 44 SNPs was found only in IBS-D group. 3. The average number of SNPs in IBS-D group, IBS-C group and control group is 12.2 ±2.7, 9.8 ± 1.8 and 9.9 ±2.1 respectively. The frequency of SNP in IBS-D group is significantly higher than IBS-C group as well as control group(P =0.01). However, no significant difference is found between the latter two groups(P=0.91) . 4. We analyzed each SNP between IBS and control and found that the frequency of 199C is significantly higher in control group compared with IBS-D group (P=0.03) , but no significant difference is found between IBS-C group and control group.Conclusions: SNP frequency of mitochondrial DNA D-loop region in patients with IBS-D is significantly higher, which suggests that SNPs of D-loop region may play some role in the pathogenesis of IBS-D. Genotype of 199C may decrease the risk of IBS-D.