APOE and AD concordance in twin pairs as predictors of AD in first-degree relatives

Objective: To examine the independent effects of the APOE genotype (APOE) a nd concordance for AD in tu in pairs on the occurrence of AD in first-degre e relatives. Background: Studies of twins have been undertaken to investiga te the influence of genes in a variety of conditions, including AD. A previ ous study, performed before reports linking APOE to AD, demonstrated an inc rease in AD among first-degree relatives of twins concordant for AD compare d with relatives-of discordant twins. Methods: In a sample of 94 twin pairs the authors examined the association between concordance for AD within the twin pair and family history of AD among first-degree relatives of twins. They then examined the extent to which the presence of the APOE epsilon 4 a llele in the twin pair explains the association between concordance for AD within the twin pair and family history of AD. Results: Concordance among t wins was associated with increased risk of AD among relatives (logrank test , chi(2) = 12.558; p = 0.0004), and the presence of at least one APOE epsil on 4 allele in each member of the twin pair is also associated with increas ed risk of AD among family members (logrank test, chi(2) = 7.712; p = 0.005 5). Conclusions: APOE genotype explains:much but not all of the association between concordance among twins and increased familial risk of AD.