| Background:Liver cancer is a major global health problem globally.It was estimated that in 2012,there were approcimately 782 000 new liver cancer cases diagnosed worldwide and 746 000 deaths caused by liver cancer with its mortality rate ranking third in tumour around the world.In China,age-standardized incidence and mortality rate were 19.44 per 100 000 and 16.84 per 100 000 respectively,with the estimated 466 100 new liver cancer cases and 422 100 deaths occurring in 2015.Hepatocellular carcinoma(HCC)represents more than 90%of liver cancer.Studies proved that the etiology of HCC is complicated,HBV,HCV,alcohol intake and aflatoxin exposure were involved in the process together.In East Asia,the largest attributable fraction was due to HBV(~60%).The predictive factors of HBV-related hepatocellular carcinoma developing from chronic hepatitis B included HBV itself(Hepatitis B virus e antigen seropositivity,high viral load,genotype C)and genetic factors(leukocyte telomere length-related genetic variants,C-reactive protein genetic polymorphisms and genetic variants in STAT4 and HLA-DQ genes).Recent observational studies indicated that telomere length was associated with HCC,but the associations were inconsistent and whether they were due to confounding or reverse causation biases inherent in conventional epidemiological studies was unclear.As a result,we applied Mendelian randomization(MR)approach,which was an ideal alternative for causal inference.MR is a form of instrumental variable analysis whereby selected genetic variants related to a specific exposure of interest are utilized to statistically evaluate a causal hypothesis between the exposure and an outcome.As genotype is presumed to be randomly allocated during the process of meiosis and genotypes precede phenotype,MR addresses the issue of reverse causality.Because these genetic variants are typically unassociated with confounders,differences in the outcome between those who carry the variant and those who do not can be attributed to the difference in the exposure.To clarify the causal effects for HCC risk,we used telomere length-associated genetic variants as instrumental variables to investigate the association between telomere length and HBV-related HCC risk with a case-control study(1 538 HBV-positive HCC patients and 1 465 HBV-positive controls).Methods:Nine telomere length-related SNPs(Single Nucleotide Polymorphisms)reaching genome-wide association significant level were systematically selected as instrumental variables.Based on previous HBV-related HCC Genome-wide association studies(GWAS)data(1 538 HBV positive HCC patients and 1 465 HBV positive controls),genetic risk score(GRS)and the inverse-variance weighting method(IVW)were applied to estimate the causal effect of telomere length on HBV-related HCC risk.Because pleiotropic SNP could lead to invalidity of MR,sensitivity analyses were used to assess and control potential confounding bias:1)as to the linkage disequilibrium(LD),the weaker SNP was removed from GRS and summarized data for IVW to assess the effect again;2)the test of heterogeneity was conducted among SNPs;3)weighted median estimation,which could provide a consistent estimate if at least 50%of the weight comes from valid SNPs,was applied to estimate the odds ratio(OR)and 95%confidence interval(CI);4)Egger regression was performed to test directional bias from pleiotropy.Besides,to explore interaction of telomere length with other factors,stratified analyses were performed according to age,gender,smoking status and drinking status.At last,telomere length-associated GRS was categorized into five/ten/four groups based on its quintiles/deciles/quartiles distribution to further detect the non-linear relationship between telomere length and HBV-related HCC.A restricted cubic spline curve was plotted in the logistic regression model to describe the dose-response relationship.Results:MR analyses indicated that both GRS and IVW methods suggested a significant risk signal between genetically increased telomere length and HBV-related HCC risk(GRS:OR=2.09,95%CI 1.32-3.31,P=0.002;IVW:OR=2.24,95%CI1.39-3.62,P=0.011).Sensitivity analyses showed the moderate LD of rs8105767and rs412658(r~2=0.48),and results from GRS and IVW methods remained similar to original ones after rs412658(the weaker SNP)was removed(GRS:OR=2.14,95%CI 1.31-3.50,P=0.002;IVW:OR=2.15,95%CI 1.32-3.52,P=0.018).No significant evidence for heterogeneity(P=0.414)was observed,which suggested that the telomere length-associated variants'effects on TL were proportional to their effects on HCC risk.The result from weighted median estimation,which was tolerant towards pleiotropy,agreed with estimates from previous analyses(OR=2.52,95%CI 1.32-4.80,P=0.023).We did not detect bias(intercept=-0.05,95%CI-0.23-0.12,P=0.486)through the Egger regression approach.Sensitivity analyses indicated that no pleiotropic effects were exerted on HCC by SNPs,and interpretation of causality was free from confounding bias.Subgroup analysis did not reveal significant heterogeneity between different age,gender,smoking status and drinking status groups.A significant dose-response relationship was observed between increased risk of HCC and increased grades of telomere length after grouped by quintiles/deciles/quartiles.Futhermore,a U-shaped curve was fitted by the restricted cubic spline curve,which indicated that either short or long telomere length would increase HCC risk(P=0.002 for non-linearity test).Conclusion:In summary,our analyses indicated that telomere length is causally associated with HBV-related HCC risk by MR approach,and provided evidence for a U-shaped association between telomere length and HBV-related HCC suggesting that either long or extreme short telomeres play a role in the etiology of HBV-related HCC.Our study made valid interpretation of causality for previous inconsistent associations from observational study,and provided vital information reference for primary prevention of HCC. |
PDF Full Text Request