Issues in molecular genetic testing of individuals with suspected early-onset familial Alzheimer's disease.

The identification of mutations in the amyloid precursor protein (APP) gene associated with the presence of early-onset familial Alzheimer disease (AD) raises the possibility of their practical clinical application, at least in some circumstances, in the diagnostic assessment for AD. As a stimulus for discussion, a hypothetical, illustrative case vignette is presented. A 48-year-old man, concerned about recent memory loss and with a family history of early-onset AD, requested testing for the APP717 Val-->Ile mutation, previously identified in his relatives affected with AD. Whether the testing should be undertaken is considered in the context of the current interpretation of potential test results as well as the competency of the individual who requested the test to provide informed consent. Informed consent includes an understanding of the foreseeable risks and benefits associated with disclosure of test results. Although molecular genetic testing in particular individuals, such as the man described herein, could be appropriate, it should not be interpreted to apply in general at this stage to individuals suspected of having AD. In view of a number of caveats, including the genetic heterogeneity of AD, which significantly limits the sensitivity and specificity of the currently available genetic tests, further research and discussion is strongly recommended before widespread introduction of molecular genetic testing for individuals with suspected AD.