Gly972Arg variant of insulin receptor substrate 1 gene and colorectal cancer risk in overweight/obese subjects.

BACKGROUND: Given the major role of obesity and insulin resistance (IR) in colorectal cancer (CRC), we investigated whether genetic variants in ghrelin (GHRL), resistin (RETN) and insulin receptor substrate 1 (IRS1) were associated with CRC risk. METHODS: This study was conducted as a case-control study, and 750 subjects, including 438 controls and 312 patients with CRC, were enrolled and genotyped using the PCR-RFLP method. RESULTS: No significant differences were observed for GHRL (rs696217), RETN (rs3745367) and IRS1 (rs1801278, Gly972Arg or G972R) gene variants between the cases and controls. However, the IRS1 G972R R allele compared with the G allele and the G972R RR+GR genotype compared with the GG genotype appeared to be markers of decreased CRC susceptibility in the overweight/obese subjects (p = 0.024; odds ratio [OR] = 0.42, 95% confidence interval [95% CI], 0.20-0.91; and p = 0.048; OR = 0.42, 95% CI, 0.17-0.99, respectively). Furthermore, the R allele and RR+GR genotype were also associated with decreased risks for obesity in the patients with CRC (p = 0.007; OR = 0.35, 95% CI, 0.15-0.77; and p = 0.015; OR = 0.35, 95% CI, 0.15-0.72, respectively). CONCLUSIONS: In accordance with previous studies, our findings suggest that the IRS1 G972R R allele and RR+GR genotype have protective effects for CRC in overweight/obese patients and for obesity in patients with CRC. Nevertheless, further studies are required to confirm these findings.

An exon variant in insulin receptor gene is associated with susceptibility to colorectal cancer in women.

Given the role of insulin resistance in colorectal cancer (CRC), we explored whether genetic variants in insulin (INS), insulin receptor (INSR), insulin receptor substrate 1 (IRS1), insulin receptor substrate 2 (IRS2), insulin-like growth factor 1 (IGF1), and insulin-like growth factor binding protein 3 (IGFBP3) genes were associated with CRC risk. A total of 600 subjects, including 261 cases with CRC and 339 controls, were enrolled in this case-control study. Six polymorphisms in INS (rs689), INSR (rs1799817), IRS1 (rs1801278), IRS2 (rs1805097), IGF1 (rs5742612), and IGFBP3 (rs2854744) genes were genotyped using PCR-RFLP method. No significant difference was observed for INS, INSR, IRS1, IRS2, IGF1, and IGFBP3 genes between the cases and controls. However, the INSR rs1799817 "TT + CT" genotype and "CT" genotype compared with "CC" genotype occurred more frequently in the women with CRC than women controls (P = 0.007; OR = 1.93, 95 %CI = 1.20-3.11 and P = 0.002, OR = 2.15, 95 %CI = 1.31-3.53, respectively), and the difference remained significant after adjustment for confounding factors including age, BMI, smoking status, NSAID use, and family history of CRC (P = 0.018; OR = 1.86, 95 %CI = 1.11-3.10 and P = 0.004, OR = 2.18, 95 %CI = 1.28-3.71, respectively). In conclusion, to our knowledge, this study indicated for the first time that the INSR rs1799817 TT + CT genotype and CT genotype compared with the CC genotype had 1.86-fold and 2.18-fold increased risks for CRC among women, respectively. Furthermore, this finding is in line with previous studies which found significant associations between other variants of the INSR gene and CRC risk. Nevertheless, further studies are required to confirm our findings.

Parathyroid hormone gene rs6256 and calcium sensing receptor gene rs1801725 variants are not associated with susceptibility to colorectal cancer in Iran.

BACKGROUND: Substantial evidence from epidemiological studies has suggested that increased levels of calcium may play a protective role against colorectal cancer (CRC). Given the vital role of calcium sensing receptor (CaSR) and parathyroid hormone (PTH) in the maintenance of calcium homeostasis, we explored whether the rs1801725 (A986S) variant located in exon 7 of the CaSR gene and the rs6256 variant located in exon 3 of PTH gene might be associated with CRC risk. MATERIALS AND METHODS: In this study 860 subjects including 350 cases with CRC and 510 controls were enrolled and genotyped using PCR-RFLP methods. RESULTS: We observed no significant difference in genotype or allele frequencies between the cases with CRC and controls for both CaSR and PTH genes either before or after adjustment for confounding factors including age, BMI, sex, smoking status, and family history of CRC. Furthermore, no evidence for effect modification of any association of rs1801725 and rs6256 variants and CRC by BMI, sex, or tumor site was observed. In addition, there was no significant difference in genotype and allele frequencies between the normal weight (BMI<25 kg/m2) cases and overweight/ obese (BMI≥25 kg/m2) cases for the two SNPs. CONCLUSIONS: These data indicated that the CaSR gene A986S variant is not a genetic contributor to CRC risk in the Iranian population. Furthermore, our results suggest for the first time that PTH gene variant does not affect CRC risk. Nonetheless, further studies with larger sample size are needed to validate these findings.

Resistin -420C>G promoter variant and colorectal cancer risk.

PURPOSES: Obesity is associated with an increased risk of colorectal cancer (CRC), and ghrelin (GHRL) and resistin (RETN) are thought to be related to obesity. Our aim was to investigate whether GHRL and RETN gene variants are associated with CRC risk. MATERIALS AND METHODS: All 414 subjects, including 197 cases with CRC and 217 controls, were genotyped for the GHRL (rs26802) and RETN (rs1862513) or -420 C>G gene variants using the PCR-RFLP method. RESULTS: Our findings indicated that the RETN -420 C>G "CC" genotype, compared with the "GG" and "GC" genotypes, was a marker of decreased CRC susceptibility; the difference remained significant after adjustment for age, BMI, gender, smoking status, NSAID use, and family history of CRC (p=0.020; OR=0.52, 95% CI=0.30-0.90). Furthermore, after adjustment for confounding factors, the -420 C>G "CC" genotype, compared with the "GG" genotype, was associated with a decreased risk for CRC (p=0.044; OR=0.53, 95% CI=0.29-0.98). In addition, no significant difference was observed for the GHRL (rs26802) gene variant. CONCLUSIONS: To our knowledge, this is the first study suggesting that the RETN -420 C>G "CC" genotype is a marker of decreased CRC susceptibility. This observation is relevant from a scientific perspective and deserves further investigations.

Lack of associations between Vitamin D metabolism-related gene variants and risk of colorectal cancer.

PURPOSE: With regard to the protective effect of vitamin D against colorectal cancer (CRC), we evaluated genetic variants that might influence vitamin D metabolism: vitamin D receptor (VDR), vitamin D binding protein (GC), vitamin D 25-hydroxylase (CYP2R1), and vitamin D 25-hydroxy 1-alpha hydroxylase (CYP27B1). MATERIALS AND METHODS: A total of 657 subjects, including 303 cases with CRC and 354 controls were enrolled in this case-control study. All 657 were genotyped for the four gene variants using PCR-RFLP methods. RESULTS: In this study, no significant difference was observed for VDR (rs2238136), GC (rs4588), CYP2R1 (rs12794714), and CYP27B1 (rs3782130) gene variants in either genotype or allele frequencies between the cases with CRC and the controls and this lack of difference remained even after adjustment for age, BMI, sex, smoking status, NSAID use, and family history of CRC. Furthermore, no evidence for effect modification of the variants and CRC by BMI, sex, or tumor site was observed. CONCLUSIONS: Our findings do not support a role for VDR, GC, and CYP27B1 genes in CRC risk in our Iranian population. Another interesting finding, which to our knowledge has not been reported previously, was the lack of association with the CYP2R1 gene polymorphism. Nonetheless, our findings require confirmation and possible roles of vitamin D metabolism-related genes in carcinogenesis need to be further investigated.

Is there an association between variants in candidate insulin pathway genes IGF-I, IGFBP-3, INSR, and IRS2 and risk of colorectal cancer in the Iranian population?

BACKGROUND: Several epidemiological studies have shown associations between colorectal cancer (CRC) risk and type 2 diabetes and obesity. Any effects would be expected to be mediated through the insulin pathway. Therefore it is possible that variants of genes encoding components of the insulin pathway play roles in CRC susceptibility. In this study, we hypothesized that polymorphisms in the genes involving the insulin pathway are associated with risk of CRC. MATERIALS AND METHODS: The associations of four single nucleotide polymorphisms (SNPs) in IGF-I (rs6214), IGFBP-3 (rs3110697), INSR (rs1052371), and IRS2 (rs2289046) genes with the risk of CRC were evaluated using a case-control design with 167 CRC cases and 277 controls by the PCR-RFLP method. RESULTS: Overall, we observed no significant difference in genotype and allele frequencies between the cases and controls for the IGF-I, IGFBP-3, INSR, IRS2 gene variants and CRC before or after adjusting for confounders (age, BMI, sex, and smoking status). However, we observed that the IRS2 (rs2289046) GG genotype compared with AA+AG genotypes has a protective effect for CRC in normal weight subjects (p=0.035, OR=0.259, 95%CI= 0.074-0.907). CONCLUSIONS: These findings do not support plausible associations between polymorphic variations in IGF-I, IGFBP-3, INSR, IRS2 genes and risk of CRC. However, the evidence for a link between the IRS2 (rs2289046) variant and risk of CRC dependent on the BMI of the subjects, requires confirmation in subsequent studies with greater sample size.

The -4817 G>A (rs2238136) variant of the vitamin D receptor gene: a probable risk factor for colorectal cancer.

Vitamin D appears to have anti-tumor activities in the large bowel. Our aim was to investigate whether -4817 G>A (rs2238136) polymorphism located at 5'-untranslated region (5'-UTR) of the human vitamin D receptor (VDR) gene was associated with colorectal cancer (CRC) risk. We conducted a case-control study and VDR genotypes, determined by Bpu10I restriction endonuclease digestion of PCR-amplified DNA, were performed on 327 cases with CRC and 327 controls. The distribution of VDR -4817 G>A genotypes and alleles differed significantly between cases with CRC and controls even after adjustment for confounding factors such as age, BMI, sex, and smoking status. Individuals carrying the "AA" genotype had a 2.09-fold increased risk compared with those with "GG" genotype (P = 0.016, OR = 2.09, 95% CI = 1.15-3.78) and a 1.87-fold increased risk compared with those with "GG and GA" genotypes (P = 0.033, OR = 1.87, 95% CI = 1.05-3.33) for CRC. Furthermore, the VDR "A" allele was significantly overrepresented in cases with CRC than controls (P = 0.044; OR = 1.28, 95% CI = 1.01-1.63). Interestingly, the analysis of the SNP revealed that all these associations were stronger for women subjects than for all subjects combined. These data indicated for the first time a direct association between "AA" genotype of VDR gene -4817 G>A polymorphism and CRC, with a stronger association for female subjects. However, our findings remain to be confirmed in other populations.

Association of leptin receptor gene Gln223Arg polymorphism with susceptibility to colorectal cancer.

AIM: Leptin is a 16 kDa polypeptide hormone which secreted by adipose tissue and has an important role in energy balance, insulin pathway and inflammation, because of that it may play an important role in colorectal cancer (CRC). Leptin exerts its effect through the leptin receptor (LEPR) a member of the class I cytokine receptor family. BACKGROUND: We have investigated whether glutamine to arginine substitution (Gln223Arg) in exon 6 of the leptin receptor gene, has implications for susceptibility to CRC. PATIENTS AND METHODS: Polymerase chain reaction (PCR) and restriction enzyme digestion (RFLP) was performed to evaluate the association between the Gln223Arg polymorphism of the LEPR and CRC risk in a case-control study in 346 subjects involving 173 cases with CRC and 173 controls. RESULTS: There was no statistically evidence of significant difference in genotype and allele frequencies between the cases with CRC and controls for the Gln223Arg polymorphism of LEPR, before or after adjusting for confounders (age, BMI, sex, and smoking status). Furthermore, no significant difference was observed between the CRC cases and controls by BMI, sex and smoking status. CONCLUSION: Our findings suggest that the LEPR Gln223Arg polymorphism is not associated with the risk of CRC in Iranian population.