Observational and genetic studies of short telomeres and Alzheimer's disease in 67,000 and 152,000 individuals: a Mendelian randomization study.

Short telomeres might lead to increased risk of Alzheimer's disease, but observational analyses have been inconclusive and potentially confounded by the strong association of both telomere length and risk of Alzheimer's disease with age and adverse lifestyle. To circumvent this, analyses including single nucleotide polymorphisms associated with telomere length used in an instrumental variable analysis produces risk estimates likely free of distortions from reverse causation and of most confounding. We tested the hypothesis that short telomeres are associated with increased risk of Alzheimer's disease, observationally and causal, genetically. Telomere length was measured in 66,567 individuals, and genotyped for rs2487999 in OBFC1, rs7726159 in TERT, and rs1317082 in TERC causing lifelong telomere shortening in 98,146 individuals from two Copenhagen studies. Genetic data on 54,162 individuals from the International Genomics of Alzheimer's Project were also included. Observationally, multifactorially adjusted hazard ratio for Alzheimer's disease was 1.02 (95% CI 1.00-1.03) per 200 base pair shorter telomeres. Telomere length was 335 base pairs shorter in individuals with 6 versus 0-1 alleles (p = 5 × 10-105). Genetically, odds ratio for Alzheimer's disease was 1.08 (1.01-1.16) per 200 base pairs shorter telomeres. Similar results were found in strata of age and comorbidities. In comparative analyses, genetically predicted shorter telomeres were associated with increased risk of myocardial infarction, and with decreased risks of lung cancer and melanoma as previously reported. Short telomeres were associated observationally and causal, genetically with increased risk of Alzheimer's disease. Telomere biology is therefore a potential pathway involved in the development of Alzheimer's disease.

Short Telomere Length and Ischemic Heart Disease: Observational and Genetic Studies in 290 022 Individuals.

BACKGROUND: Short telomeres are associated with aging and have been associated with a high risk of ischemic heart disease in observational studies; however, the latter association could be due to residual confounding and/or reverse causation. We wanted to test the hypothesis that short telomeres are associated with high risk of ischemic heart disease using a Mendelian randomization approach free of reverse causation and of most confounding. METHODS: We genotyped 3 genetic variants in OBFC1 (oligonucleotide/oligosaccharide binding fold containing 1), TERT (telomerase reverse transcriptase), and TERC (telomerase RNA component), which code for proteins and RNA involved in telomere maintenance. We studied 105 055 individuals from Copenhagen; 17 235 of these individuals were diagnosed with ischemic heart disease between 1977 and 2013, and 66 618 had telomere length measured. For genetic studies, we further included the Coronary ARtery DIsease Genome wide Replication and Meta-analysis (CARDIoGRAM) consortium dataset, which included up to 184 967 participants and 60 837 cases of ischemic heart disease. We conducted multivariable adjusted Cox proportional hazard models for observational estimates, using logistic and instrumental variable analysis for genetic estimates. RESULTS: Observationally, a 200-bp-shorter telomere length was associated with a multivariable adjusted hazard ratio for ischemic heart disease of 1.02 (95% CI, 1.01-1.03). Per allele, telomeres were shorter by 67 bp (73-60). In meta-analyses of all 4 studies combined, odds ratios for ischemic heart disease were 1.05 (1.03-1.08) for OBCF1, 1.04 (1.02-1.06) for TERT, and 1.01 (0.99-1.03) for TERC. A genetically determined 200-bp-shorter telomere length was associated with an odds ratio for ischemic heart disease of 1.10 (1.06-1.14). CONCLUSIONS: Shorter telomeres were associated with a higher risk of ischemic heart disease, both observationally and genetically.