Influence of premorbid IQ and education on progression of Alzheimer's disease.

ABSTRACT

BACKGROUND: Lower education is associated with a higher risk of developing Alzheimer's disease (AD). Years of education and measures of general intellectual function (IQ) are highly correlated. It is important to determine whether there is a relationship between education and AD outcomes that is independent of IQ. OBJECTIVE: To test the hypothesis that premorbid IQ is a stronger predictor of cognitive decline, global progression, and overall survival, than education in patients with AD. METHODS: The study included 478 probable AD patients (322 women and 156 men, mean age 74.5 years) followed in a large AD referral center for a mean of 3.2 years. Eligible participants had a baseline estimate of premorbid IQ using the American version of the Nelson Adult Reading Test (AMNART) and at least one follow-up visit with complete neuropsychological assessment. We used random effects linear regression analysis, and Cox proportional hazards analysis to determine whether or not education and/or premorbid IQ were independently associated with cognitive decline, global progression of AD, and survival. RESULTS: When the baseline AMNART score was included in regression models along with education and other demographic variables, AMNART score, but not education, was associated with a higher baseline score and slower rate of decline in MMSE and ADAS-Cog scores, and the Clinical Dementia Rating sum of boxes score. Neither higher premorbid IQ nor higher education was associated with longer survival. CONCLUSIONS: We conclude that a baseline AMNART score is a better predictor of cognitive change in AD than education, but neither variable is associated with survival after diagnosis.