title: Accounting for the relationship between low education and dementia: a twin study.
abstract: We evaluated whether the association between low education and greater risk of dementia is explained by genetic influences, using three different types of analyses. The HARMONY study (Swedish for "health" (Hälsa), "genes" (ARv), "environment" (Miljö), "and" (Och), and "new" (NY)) includes members of the Swedish Twin Registry who were aged 65 and older and alive in 1998, and who were screened and clinically assessed for dementia. There were 394 cases with dementia and 7786 unrelated controls. Analyses included co-twin control, tests for association between education and a measured genotype, and bivariate twin modeling. Low education was a significant risk factor for dementia both in case-control analyses (odds ratio=1.77, 95% confidence interval 1.38 to 2.28) and co-twin control analyses with monozygotic twin pairs (odds ratio=3.17, 95% confidence interval 1.26 to 7.93). Apolipoprotein E genotype was not associated with education and did not account for the relationship between education and dementia. Bivariate twin modeling showed that the association between education and dementia was not mediated by genetic influences in common between education and dementia. The association was mediated by shared environmental influences that were related to both dementia and to education. Low education is confirmed as a risk factor for dementia. Findings from three different analytic approaches showed that genetic influences did not explain this association.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Box 281, S-171 77 Stockholm, Sweden.
authors.forename: Margaret
authors.initials: M
authors.lastname: Gatz
authors.forename: James A
authors.initials: JA
authors.lastname: Mortimer
authors.forename: Laura
authors.initials: L
authors.lastname: Fratiglioni
authors.forename: Boo
authors.initials: B
authors.lastname: Johansson
authors.forename: Stig
authors.initials: S
authors.lastname: Berg
authors.forename: Ross
authors.initials: R
authors.lastname: Andel
authors.forename: Michael
authors.initials: M
authors.lastname: Crowe
authors.forename: Amy
authors.initials: A
authors.lastname: Fiske
authors.forename: Chandra A
authors.initials: CA
authors.lastname: Reynolds
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Pedersen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D053327:Apolipoprotein E4 / Q000235:genetics* / Q000378:metabolism; D016022:Case-Control Studies; D015331:Cohort Studies; D003704:Dementia / Q000235:genetics* / Q000378:metabolism; D004200:Diseases in Twins; D004522:Educational Status; D004777:Environment; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D015233:Models, Statistical; D012042:Registries; D012307:Risk Factors; D013548:Sweden; D014430:Twins, Monozygotic
chemical_list: D053327:Apolipoprotein E4