Rotterdam Study (RS) – is a population-based cohort study among inhabitants of a district of Rotterdam (Ommoord), The Netherlands, and aims to examine the determinants of disease and health in the elderly with a focus on neurogeriatric, cardiovascular, bone, and eye disease. In 1990 to 1993, 7983 persons participated and were re-examined every 3 to 4 years (Rotterdam Study I). In 2000 to 2001 the cohort was expanded by 3011 persons who had not yet been part of the Rotterdam Study (Rotterdam Study II). All participants had DNA extracted at their first visit. In 2006-2008 a second expansion (Rotterdam Study III) of 3,932 persons aged 45 and over was realized. Genotyping was performed at the Human Genotyping Facility, Genetic Laboratory Department of Internal Medicine, Erasmus MC, Rotterdam. Genotypes were imputed to the 1000 genomes phase I version 3 reference panel, using standard methods and software. The Rotterdam Study has been approved by the Medical Ethics Committee of the Erasmus MC and by the Ministry of Health, Welfare and Sport of the Netherlands, implementing the Wet Bevolkingsonderzoek: ERGO (Population Studies Act: Rotterdam Study). All participants provided written informed consent to participate in the study and to obtain information from their treating physicians.
Population-based estimates of heritability were calculated using Genome-wide Complex Trait Analysis ( Yang, et al GCTA v1.24 ) in the population-based Rotterdam Study. GCTA implements REML (restricted maximum likelihood) analysis, this method compares genotypic similarity between individuals to their phenotypic similarity. The 1000 Genomes imputed genotypes were filtered on imputation quality (Imputation quality < 0.5) and allele frequency (MAF < 0.01%) to create a genetic related matrix. In the voxel-wise analysis the three cohorts of the Rotterdam study were combined in a single analysis. Pairwise genetic relatedness between all individuals was calculated and for pairs with more than 0.02 genotype similarity one person was removed (N removed = 832) (Adams, et al., 2015 ). REML analysis was then performed in the remaining 3239 unrelated subjects using the genetic related matrix correcting for age and gender. All grey matter heritability was estimated once, heritability estimates with invalid standard errors were excluded
Erasmus Rucphen Family (ERF) – is a family-based cohort study in a genetically isolated population from a community in the South-West of the Netherlands (Rucphen municipality) including 3000 participants. Participants are all descendants of a limited number of founders living in the 19th century, and all of Caucasian European descent. Extensive genealogical data is available for this population. The study population is described in detail elsewhere. In a follow-up analysis, non-demented hypertensive (SBP ≥ 160, DBP ≥ 100 or use of antihypertensive medication) subjects aged 55-75 years were included for a new battery of tests including MRI scanning. These 122 participants from the ERF could be connected in three generations. The resulting large pedigree was split into multiple small pedigrees with a maximum bit size of 24 (pedcut version 1.19). All participants gave informed consent to participate in the study and to obtain information from their treating physicians. The study was approved by the medical ethics committee at Erasmus MC University Medical Center.
Austrian Stroke Prevention Study (ASPS) - is a single-center, prospective follow-up study on the effects of vascular risk factors on brain structure and function in the normal elderly population of the city of Graz, Austria. The procedure of recruitment and diagnostic work-up of study participants has been described previously. A total of 2007 participants were randomly selected from the official community register stratified by gender and 5-year age groups. Individuals were excluded from the study if they had a history of neuropsychiatric disease, including previous stroke, transient ischemic attacks, and dementia, or if they had an abnormal neurologic examination determined on the basis of a structured clinical interview and a physical and neurologic examination. During 2 study periods between September 1991 and March 1994, and between January 1999 and December 2003, an extended diagnostic work-up including MRI and neuropsychological testing was performed in 1076 individuals aged 45 to 85 years randomly selected from the entire cohort (509 from the first period and 567 from the second). Between 2006 and 2013 the study was extended for the Austrian Stroke Prevention Family Study (ASPS-Fam). Study participants of the ASPS and their first grade relatives were invited to enter ASPS-Fam. Inclusion criteria again were no history of previous stroke or dementia and a normal neurological examination. A total of 381 individuals from 169 families were included into the study. The number of members per family ranged from 2 to 6. The diagnostic work-up was identical to the original study. The study protocol was approved by the ethics committee of the Medical University of Graz, Austria, and written and informed consent was obtained from all subjects.
Family-based heritability was estimated using maximum-likelihood variance components methods implemented in the SOLAR(version 6.6.2) (Almasy and Blangero) software. We did not jointly analyse the ERF study and ASPS-Fam, because ERF subjects were scanned on a 1.5 T and ASPS-Fam subjects on 3.0 T. Instead inverse variance meta-analysis using heritability and heritability standard errors was performed in METAL ( as described in Jahanshad, et al.). Heritability estimates were calculated in both studies with age and gender as covariates. Heritability estimates with too high residual kurtosis and estimates of 0 with invalid standard errors were excluded from the meta-analysis. Missing standard error of valid heritability estimates of 1 were imputed to the minimum standard error.