A comparison of family history of psychiatric disorders among patients with early- and late-onset Alzheimer's disease

Objective: Both early-onset Alzheimer's disease (EOAD) and late-onset Alzheimer's disease (LOAD) present with cognitive and psychiatric features. Some studies suggest that EOAD patients are more likely than LOAD patients to have psychiatric symptoms. If this is true, relatives of EOAD patients with a similar clinical presentation may be more likely to be misclassifled as having a primary noncognitive psychiatric disorder rather than a dementing disorder. Family history studies may underestimate familial aggregation of EOAD. Methods: The authors compared the presence of psychiatric symptoms in parents and siblings of 131 EOAD patients (diagnosed at or before age 60), with the parents and siblings of 131 LOAD patients (diagnosed at or after age 65). Early onset Alzheimer's disease and LOAD patients were matched for diagnosis (probable versus possible AD), gender, and ethnic group. Logistic regression analysis was performed on the outcome variable of patient group (EOAD, LOAD) with family history of psychiatric symptoms as the risk factor, adjusting for family size and patient's education. Results: There was a nearly two and one-half-fold increase in family history of psychiatric symptoms among EOAD patients when compared with LOAD patients (RR 2.4; 95% C.I. 1.2-4.7). Conclusions: The authors found preliminary evidence of a higher prevalence of a history of psychiatric symptoms among relatives of EOAD patients when compared to LOAD patients. This may be due to differential misclassification of AD, a syndromic disorder with both noncognitive psychiatric and cognitive deficits in relatives of EOAD patients. Alternatively, shared genetic or other familial etiologies may underlie subtypes of EOAD and some psychiatric disorders.