To know or not to know: an update of the literature on the psychological and behavioral impact of genetic testing for Alzheimer disease risk.

Alzheimer disease (AD) is a genetically heterogenous disorder; in rare cases autosomal dominantly inherited mutations typically cause early-onset familial AD (EOAD), whereas the risk for late-onset AD (LOAD) is generally modulated by genetic variants with relatively low penetrance but high prevalence, with variants in apolipoprotein E (APOE) being a firmly established risk factor. This article presents an overview of the current literature on the psychological and behavioral impact of genetic testing for AD. The few studies available for presymptomatic testing for EOAD showed that only a very small proportion of individuals had poor psychological outcomes as a result. Initial interest in testing for EOAD decreases significantly after identification of a specific mutation in a kindred, suggesting that interest and potential for knowledge may not translate into actual testing uptake. The majority of individuals from both the general population and those with a family history of AD had positive attitudes towards, and were interested in, susceptibility testing for APOE. Motivations for genetic testing included to provide information for future planning and to learn about one's own and one's children's risks of developing AD. Although susceptibility testing for APOE genotype is not currently recommended due to the lack of clinical utility, this review demonstrates that there is interest in testing and no obvious adverse psychological effects to those who have been tested.