Mendelian randomization study on the causal relationship between leukocyte telomere length and prostate cancer

Causal Links Between Bone Diseases and Temporomandibular Disorders

INTRODUCTION AND AIMS

Epidemiological observational studies have explored the link between bone joint-related diseases and temporomandibular disorders (TMD), but inconsistent conclusions have emerged due to various limitations. This study aims to investigate the causal relationship between bone joint-related diseases and TMD using Mendelian randomization (MR).

METHODS

We utilized a two-sample MR design, applying pooled genome-wide association study (GWAS) data from six subtypes of bone and joint diseases and TMD. Primary analysis was conducted using the inverse-variance weighted (IVW) method, complemented by weighted median (WM), weighted mode, and MR-Egger regression to assess causal relationships. Additionally, we performed reverse causality analyses and applied sensitivity analyses, including MR-PRESSO, MR-Egger, Cochran's Q, and leave-one-out methods to evaluate result robustness, explore heterogeneity, and identify potential biases.

RESULTS

MR genetic prediction analyses indicated that bone and joint-related diseases increase the risk of TMD, with specific odds ratios (OR) for ankylosing spondylitis (AS: OR 1.36, 95% CI: 1.04-1.77, P = .026), rheumatoid arthritis (RA: OR 1.08, 95% CI: 1.03-1.13, P = .001), and osteoporosis (OR 1.0751, 95% CI: 1.0047-1.1505, P = .036). Conversely, reverse MR analysis revealed a positive genetic link from TMD to RA (RA: OR 1.12, 95% CI: 1.02-1.23, P = .018). MR-Egger regression showed no influence of horizontal pleiotropy, and MR-PRESSO detected no outliers. The leave-one-out analysis confirmed the results' stability.

CONCLUSIONS

The findings demonstrate a positive, causal association between TMD risk and AS, RA, and osteoporosis. Moreover, TMD patients exhibit an increased risk of developing RA.

CLINICAL RELEVANCE

Understanding these relationships aids in better diagnosis and management of TMD and its association with bone joint diseases, potentially guiding clinical interventions.

Long or short? Telomere length and pancreatic cancer and its precursor lesions, a narrative review

Pancreatic ductal adenocarcinoma (PDAC) is the most common and lethal form of pancreatic cancer, with a survival approaching only 11% at 5 years after diagnosis. In the last 15 years, telomere length (TL) measured in leukocyte (LTL) has been studied in relation to PDAC risk. The majority of the studies reported an association between short LTL and increased PDAC risk, but the results are heterogeneous. Genome-wide association studies have identified several single-nucleotide polymorphisms (SNPs) in the telomerase reverse transcriptase (TERT) gene as susceptibility loci for PDAC. Polygenic risk scores computed using SNPs associated with LTL have been tested in relation to PDAC susceptibility with various methods and giving contrasting results. The aim of this review is to analyze all publications carried out specifically on LTL, considering LTL measured with qPCR and with genetic proxies, and PDAC risk. Additionally, we will give an overview of the most relevant associations between SNPs in telomere-associated genes and PDAC, to answer the question shorter or longer? Which one of the two is associated with PDAC risk?

Absence of genetic association between insulin-like growth factors and esophageal cancer

This study aimed to explore the causal relationship between concentrations of various insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs) and esophageal cancer (ESC), addressing the gap in understanding the genetic link between IGF1 and ESC. A two-sample Mendelian randomization (MR) analysis was conducted using single nucleotide polymorphisms linked to IGFs/IGFBPs and ESC from the IEU Open GWAS Project. This analysis included ESC GWAS data from 1996 individuals of European descent and genetic variant data from 3310 individuals of European ancestry. Various methods, such as inverse variance weighting, weighted median, weighted mode, and MR-Egger regression, were applied for analysis, with sensitivity assessments including MR-PRESSO, Cochran Q, and leave-one-out analysis to ensure the robustness of results and detect biases. The genetic predictions indicated no significant association between IGFs/IGFBPs and ESC. When ESC was the outcome measure, the odds ratios with 95% confidence intervals were as follows: IGF1 = 1.00 (0.89-1.12, P = .936), IGF1R = 1.07 (0.90-1.27, P = .453), IGFBP3 = 1.00 (0.79-1.26, P = .975), and IGFBPL1 = 0.91 (0.75-1.12, P = .372). MR-Egger regression confirmed the absence of horizontal pleiotropy, and no outliers were identified by MR-PRESSO. Leave-one-out analysis supported the stability of the results. The study did not find a causal connection between IGFs/IGFBPs and ESC. These results suggest the need for further validation and potentially highlight the complex interplay of factors involved in the development of ESC.

Investigating the Shared Genetic Architecture Between Leukocyte Telomere Length and Prostate Cancer

PURPOSE

Evidence of an association between leukocyte telomere length (LTL) and prostate cancer (PCa) is accumulating; however, their shared genetic basis remains unclear.

MATERIALS AND METHODS

Using summary statistics obtained from the genome-wide association study (GWAS), we quantified the global and local genetic correlations between two traits. Subsequently, we identified potential pleiotropic loci, common tissue-enriched regions, and risk gene loci while inferring assumed causal relationships.

RESULTS

Our study demonstrated a global genetic correlation between LTL and PCa (genetic correlation=0.066, p=0.017), which was further confirmed in local genomic regions. Cross-trait GWAS meta-analysis revealed 44 shared loci, including 10 novel pleiotropic single nucleotide polymorphisms appearing concurrently in significant local genetic correlation regions. Notably, two new loci (rs9419958; rs3730668) were additionally validated to co-localize. For the first time, we identified a significant shared genetic enrichment of both traits in the small intestine tissue at the terminal ileum, with functional genes in this region affecting both LTL and PCa. Concurrently, Mendelian randomization analysis indicated a positive causal relationship between LTL and PCa.

CONCLUSIONS

In conclusion, our study makes a significant contribution to the ongoing debate concerning the potential association between longer LTL and a higher risk of PCa. Additionally, we provide new evidence for the development of therapeutic targets for PCa and propose new directions for future risk prediction in this regard.

Leucocyte Telomere Length and Lung Cancer Risk: A Systematic Review and Meta-Analysis of Prospective Studies

Although numerous epidemiological studies are available, the relationship between leukocyte telomere length (LTL) and lung cancer risk is still controversial. This systematic review and meta-analysis, performed according to the PRISMA statement and MOOSE guidelines, aims to summarize the evidence and calculate the risk of lung cancer associated with LTL. The literature search was performed on PubMed, Web of Science, and Scopus databases through May 2024. A random-effects model was used to calculate the pooled risk. Heterogeneity was assessed using I2 and Cochran's Q statistic. Begg's and Egger's tests were used to detect publication bias. Based on 8055 lung cancer cases and 854,653 controls (nine prospective studies), longer LTL was associated with a significant 42% increment in all types of lung cancer risk (OR 1.42, 95% CI 1.24-1.63). The effect was even more evident for adenocarcinomas (OR 1.98, 95% CI 1.69-2.31), while no association was observed for squamous cell carcinoma (OR 0.87, 95% CI 0.72-1.06). Significantly, no association was found for current smokers (OR 1.08, 95% CI 0.90-1.30), while it remained high for both never-smokers (OR 1.92, 95% CI 1.62-2.28) and former smokers (OR 1.34, 95% CI 1.11-1.62). No significant publication bias was evidenced. Longer LTL is associated with an increment in lung cancer risk particularly in never-smoker subjects.

Mendelian randomization evidence based on European ancestry for the causal effects of leukocyte telomere length on prostate cancer

BACKGROUND

Several lines of evidence suggest that leukocyte telomere length (LTL) can affect the development of prostate cancer (PC).

METHODS

Here, we employed single nucleoside polymorphisms (SNPs) as instrumental variables (IVs) for LTL (n = 472,174) and conducted Mendelian randomization analysis to estimate their causal impact on PCs (79,148 patients/61,106 controls and 6311 patients/88,902 controls).

RESULTS

Every 1-s.d extension of LTL increased the risk of PCs by 34%. Additionally, the analysis of candidate mediators between LTL and PCs via two-step Mendelian randomization revealed that among the 23 candidates, Alzheimer's disease, liver iron content, sex hormone binding global levels, naive CD4-CD8-T cell% T cell, and circulating leptin levels played substantial mediating roles. There is no robust evidence to support the reverse causal relationship between LTL and the selected mediators of PCs. Adjusting for the former four mediators, rather than adjusting for circulating leptin levels, decreased the impact of LTL on PCs.

CONCLUSION

This study provides potential intervention measures for preventing LTL-induced PCs.

Breaking down causes, consequences, and mediating effects of telomere length variation on human health

BACKGROUND

Telomeres form repeated DNA sequences at the ends of chromosomes, which shorten with each cell division. Yet, factors modulating telomere attrition and the health consequences thereof are not fully understood. To address this, we leveraged data from 326,363 unrelated UK Biobank participants of European ancestry.

RESULTS

Using linear regression and bidirectional univariable and multivariable Mendelian randomization (MR), we elucidate the relationships between leukocyte telomere length (LTL) and 142 complex traits, including diseases, biomarkers, and lifestyle factors. We confirm that telomeres shorten with age and show a stronger decline in males than in females, with these factors contributing to the majority of the 5.4% of LTL variance explained by the phenome. MR reveals 23 traits modulating LTL. Smoking cessation and high educational attainment associate with longer LTL, while weekly alcohol intake, body mass index, urate levels, and female reproductive events, such as childbirth, associate with shorter LTL. We also identify 24 traits affected by LTL, with risk for cardiovascular, pulmonary, and some autoimmune diseases being increased by short LTL, while longer LTL increased risk for other autoimmune conditions and cancers. Through multivariable MR, we show that LTL may partially mediate the impact of educational attainment, body mass index, and female age at childbirth on proxied lifespan.

CONCLUSIONS

Our study sheds light on the modulators, consequences, and the mediatory role of telomeres, portraying an intricate relationship between LTL, diseases, lifestyle, and socio-economic factors.

New insights from bidirectional Mendelian randomization: causal relationships between telomere length and mitochondrial DNA copy number in aging biomarkers

Mitochondrial DNA (mtDNA) copy number and telomere length (TL) are dynamic factors that have been linked to the aging process in organisms. However, the causal relationship between these variables remains uncertain. In this research, instrumental variables (IVs) related to mtDNA copy number and TL were obtained from publicly available genome-wide association studies (GWAS). Through bidirectional Mendelian randomization (MR) analysis, we examined the potential causal relationship between these factors. The forward analysis, with mtDNA copy number as the exposure and TL as the outcome, did not reveal a significant effect (B=-0.004, P>0.05). On the contrary, upon conducting a reverse analysis, it was found that there exists a positive causal relationship (B=0.054, P<0.05). Sensitivity analyses further confirmed the reliability of these results. The outcomes of this study indicate a one-way positive causal relationship, indicating that telomere shortening in the aging process may lead to a decrease in mtDNA copy number, providing new perspectives on their biological mechanisms.

Assessing the causal link between liver function and acute pancreatitis: A Mendelian randomisation study

A correlation has been reported to exist between exposure factors (e.g. liver function) and acute pancreatitis. However, the specific causal relationship remains unclear. This study aimed to infer the causal relationship between liver function and acute pancreatitis using the Mendelian randomisation method. We employed summary data from a genome-wide association study involving individuals of European ancestry from the UK Biobank and FinnGen. Single-nucleotide polymorphisms (SCNPs), closely associated with liver function, served as instrumental variables. We used five regression models for causality assessment: MR-Egger regression, the random-effect inverse variance weighting method (IVW), the weighted median method (WME), the weighted model, and the simple model. We assessed the heterogeneity of the SNPs using Cochran's Q test. Multi-effect analysis was performed using the intercept term of the MR-Egger method and leave-one-out detection. Odds ratios (ORs) were used to evaluate the causal relationship between liver function and acute pancreatitis risk. A total of 641 SNPs were incorporated as instrumental variables. The MR-IVW method indicated a causal effect of gamma-glutamyltransferase (GGT) on acute pancreatitis (OR = 1.180, 95%CI [confidence interval]: 1.021-1.365, P = 0.025), suggesting that GGT may influence the incidence of acute pancreatitis. Conversely, the results for alkaline phosphatase (ALP) (OR = 0.997, 95%CI: 0.992-1.002, P = 0.197) and aspartate aminotransferase (AST) (OR = 0.939, 95%CI: 0.794-1.111, P = 0.464) did not show a causal effect on acute pancreatitis. Additionally, neither the intercept term nor the zero difference in the MR-Egger regression attained statistical significance (P = 0.257), and there were no observable gene effects. This study suggests that GGT levels are a potential risk factor for acute pancreatitis and may increase the associated risk. In contrast, ALP and AST levels did not affect the risk of acute pancreatitis.

Risk factors for prostate cancer: An umbrella review of prospective observational studies and mendelian randomization analyses

BACKGROUND

The incidence of prostate cancer is increasing in older males globally. Age, ethnicity, and family history are identified as the well-known risk factors for prostate cancer, but few modifiable factors have been firmly established. The objective of this study was to identify and evaluate various factors modifying the risk of prostate cancer reported in meta-analyses of prospective observational studies and mendelian randomization (MR) analyses.

METHODS AND FINDINGS

We searched PubMed, Embase, and Web of Science from the inception to January 10, 2022, updated on September 9, 2023, to identify meta-analyses and MR studies on prostate cancer. Eligibility criteria for meta-analyses were (1) meta-analyses including prospective observational studies or studies that declared outcome-free at baseline; (2) evaluating the factors of any category associated with prostate cancer incidence; and (3) providing effect estimates for further data synthesis. Similar criteria were applied to MR studies. Meta-analysis was repeated using the random-effects inverse-variance model with DerSimonian-Laird method. Quality assessment was then conducted for included meta-analyses using AMSTAR-2 tool and for MR studies using STROBE-MR and assumption evaluation. Subsequent evidence grading criteria for significant associations in meta-analyses contained sample size, P values and 95% confidence intervals, 95% prediction intervals, heterogeneity, and publication bias, assigning 4 evidence grades (convincing, highly suggestive, suggestive, or weak). Significant associations in MR studies were graded as robust, probable, suggestive, or insufficient considering P values and concordance of effect directions. Finally, 92 selected from 411 meta-analyses and 64 selected from 118 MR studies were included after excluding the overlapping and outdated studies which were published earlier and contained fewer participants or fewer instrument variables for the same exposure. In total, 123 observational associations (45 significant and 78 null) and 145 causal associations (55 significant and 90 null) were categorized into lifestyle; diet and nutrition; anthropometric indices; biomarkers; clinical variables, diseases, and treatments; and environmental factors. Concerning evidence grading on significant associations, there were 5 highly suggestive, 36 suggestive, and 4 weak associations in meta-analyses, and 10 robust, 24 probable, 4 suggestive, and 17 insufficient causal associations in MR studies. Twenty-six overlapping factors between meta-analyses and MR studies were identified, with consistent significant effects found for physical activity (PA) (occupational PA in meta: OR = 0.87, 95% CI: 0.80, 0.94; accelerator-measured PA in MR: OR = 0.49, 95% CI: 0.33, 0.72), height (meta: OR = 1.09, 95% CI: 1.06, 1.12; MR: OR = 1.07, 95% CI: 1.01, 1.15, for aggressive prostate cancer), and smoking (current smoking in meta: OR = 0.74, 95% CI: 0.68, 0.80; smoking initiation in MR: OR = 0.91, 95% CI: 0.86, 0.97). Methodological limitation is that the evidence grading criteria could be expanded by considering more indices.

CONCLUSIONS

In this large-scale study, we summarized the associations of various factors with prostate cancer risk and provided comparisons between observational associations by meta-analysis and genetically estimated causality by MR analyses. In the absence of convincing overlapping evidence based on the existing literature, no robust associations were identified, but some effects were observed for height, physical activity, and smoking.