@article {1171,
	title = {Bayesian methods for meta-analysis of causal relationships estimated using genetic instrumental variables.},
	journal = {Stat Med},
	volume = {29},
	year = {2010},
	month = {2010 May 30},
	pages = {1298-311},
	abstract = {<p>Genetic markers can be used as instrumental variables, in an analogous way to randomization in a clinical trial, to estimate the causal relationship between a phenotype and an outcome variable. Our purpose is to extend the existing methods for such Mendelian randomization studies to the context of multiple genetic markers measured in multiple studies, based on the analysis of individual participant data. First, for a single genetic marker in one study, we show that the usual ratio of coefficients approach can be reformulated as a regression with heterogeneous error in the explanatory variable. This can be implemented using a Bayesian approach, which is next extended to include multiple genetic markers. We then propose a hierarchical model for undertaking a meta-analysis of multiple studies, in which it is not necessary that the same genetic markers are measured in each study. This provides an overall estimate of the causal relationship between the phenotype and the outcome, and an assessment of its heterogeneity across studies. As an example, we estimate the causal relationship of blood concentrations of C-reactive protein on fibrinogen levels using data from 11 studies. These methods provide a flexible framework for efficient estimation of causal relationships derived from multiple studies. Issues discussed include weak instrument bias, analysis of binary outcome data such as disease risk, missing genetic data, and the use of haplotypes.</p>},
	keywords = {Bayes Theorem, Biostatistics, C-Reactive Protein, Fibrinogen, Genetic Markers, Humans, Meta-Analysis as Topic, Models, Statistical, Phenotype, Polymorphism, Single Nucleotide},
	issn = {1097-0258},
	doi = {10.1002/sim.3843},
	author = {Burgess, Stephen and Thompson, Simon G and Burgess, S and Thompson, S G and Andrews, G and Samani, N J and Hall, A and Whincup, P and Morris, R and Lawlor, D A and Davey Smith, G and Timpson, N and Ebrahim, S and Ben-Shlomo, Y and Davey Smith, G and Timpson, N and Brown, M and Ricketts, S and Sandhu, M and Reiner, A and Psaty, B and Lange, L and Cushman, M and Hung, J and Thompson, P and Beilby, J and Warrington, N and Palmer, L J and Nordestgaard, B G and Tybjaerg-Hansen, A and Zacho, J and Wu, C and Lowe, G and Tzoulaki, I and Kumari, M and Sandhu, M and Yamamoto, J F and Chiodini, B and Franzosi, M and Hankey, G J and Jamrozik, K and Palmer, L and Rimm, E and Pai, J and Psaty, B and Heckbert, S and Bis, J and Anand, S and Engert, J and Collins, R and Clarke, R and Melander, O and Berglund, G and Ladenvall, P and Johansson, L and Jansson, J-H and Hallmans, G and Hingorani, A and Humphries, S and Rimm, E and Manson, J and Pai, J and Watkins, H and Clarke, R and Hopewell, J and Saleheen, D and Frossard, R and Danesh, J and Sattar, N and Robertson, M and Shepherd, J and Schaefer, E and Hofman, A and Witteman, J C M and Kardys, I and Ben-Shlomo, Y and Davey Smith, G and Timpson, N and de Faire, U and Bennet, A and Sattar, N and Ford, I and Packard, C and Kumari, M and Manson, J and Lawlor, Debbie A and Davey Smith, George and Anand, S and Collins, R and Casas, J P and Danesh, J and Davey Smith, G and Franzosi, M and Hingorani, A and Lawlor, D A and Manson, J and Nordestgaard, B G and Samani, N J and Sandhu, M and Smeeth, L and Wensley, F and Anand, S and Bowden, J and Burgess, S and Casas, J P and Di Angelantonio, E and Engert, J and Gao, P and Shah, T and Smeeth, L and Thompson, S G and Verzilli, C and Walker, M and Whittaker, J and Hingorani, A and Danesh, J}
}
@article {7564,
	title = {Short telomere length is associated with impaired cognitive performance in European ancestry cohorts.},
	journal = {Transl Psychiatry},
	volume = {7},
	year = {2017},
	month = {2017 04 18},
	pages = {e1100},
	abstract = {<p>The association between telomere length (TL) dynamics on cognitive performance over the life-course is not well understood. This study meta-analyses observational and causal associations between TL and six cognitive traits, with stratifications on APOE genotype, in a Mendelian Randomization (MR) framework. Twelve European cohorts (N=17 052; mean age=59.2{\textpm}8.8 years) provided results for associations between qPCR-measured TL (T/S-ratio scale) and general cognitive function, mini-mental state exam (MMSE), processing speed by digit symbol substitution test (DSST), visuospatial functioning, memory and executive functioning (STROOP). In addition, a genetic risk score (GRS) for TL including seven known genetic variants for TL was calculated, and used in associations with cognitive traits as outcomes in all cohorts. Observational analyses showed that longer telomeres were associated with better scores on DSST (β=0.051 per s.d.-increase of TL; 95\% confidence interval (CI): 0.024, 0.077; P=0.0002), and MMSE (β=0.025; 95\% CI: 0.002, 0.047; P=0.03), and faster STROOP (β=-0.053; 95\% CI: -0.087, -0.018; P=0.003). Effects for DSST were stronger in APOE ɛ4 non-carriers (β=0.081; 95\% CI: 0.045, 0.117; P=1.0 {\texttimes} 10-5), whereas carriers performed better in STROOP (β=-0.074; 95\% CI: -0.140, -0.009; P=0.03). Causal associations were found for STROOP only (β=-0.598 per s.d.-increase of TL; 95\% CI: -1.125, -0.072; P=0.026), with a larger effect in ɛ4-carriers (β=-0.699; 95\% CI: -1.330, -0.069; P=0.03). Two-sample replication analyses using CHARGE summary statistics showed causal effects between TL and general cognitive function and DSST, but not with STROOP. In conclusion, we suggest causal effects from longer TL on better cognitive performance, where APOE ɛ4-carriers might be at differential risk.</p>},
	keywords = {Adult, Aged, Apolipoprotein E4, Cognitive Dysfunction, Cohort Studies, European Continental Ancestry Group, Female, Genetic Carrier Screening, Genotype, Humans, Male, Mendelian Randomization Analysis, Middle Aged, Neuropsychological Tests, Psychometrics, Statistics as Topic, Telomere},
	issn = {2158-3188},
	doi = {10.1038/tp.2017.73},
	author = {H{\"a}gg, S and Zhan, Y and Karlsson, R and Gerritsen, L and Ploner, A and van der Lee, S J and Broer, L and Deelen, J and Marioni, R E and Wong, A and Lundquist, A and Zhu, G and Hansell, N K and Sillanp{\"a}{\"a}, E and Fedko, I O and Amin, N A and Beekman, M and de Craen, A J M and Degerman, S and Harris, S E and Kan, K-J and Martin-Ruiz, C M and Montgomery, G W and Adolfsson, A N and Reynolds, C A and Samani, N J and Suchiman, H E D and Viljanen, A and von Zglinicki, T and Wright, M J and Hottenga, J-J and Boomsma, D I and Rantanen, T and Kaprio, J A and Nyholt, D R and Martin, N G and Nyberg, L and Adolfsson, R and Kuh, D and Starr, J M and Deary, I J and Slagboom, P E and van Duijn, C M and Codd, V and Pedersen, N L}
}
