Background: The risk of Alzheimer's disease (AD) appears to increase, and the age at onset to decrease, with the number of epsilon 4 alleles. If this relationship is due to increased rate of pathophysiological change, the presence of epsilon 4 would be expected to influence progression of disease, predicting a more rapid decline with increasing number of epsilon 4 alleles.
Objective: To determine if the frequency of the epsilon 4 allele of the apolipoprotein E (ApoE) gene affects the rate of clinical progression in AD.
Setting: Alzheimer's Disease Research Center.
Subjects: One hundred one subjects meeting criteria of the National Institute of Neurological Disorders and Stroke for probable AD or of the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) for definite AD; 78 of these subjects met the additional criterion of having a Mini-Mental State Examination score of at least 10 for analysis of rate of decline.
Measurements: The subjects' characteristics and neuropsychological battery, including the Mini-Mental state Examination, Spatial Delayed Recognition Span, Boston Naming Test, Category Fluency Test, and the Physical Capacity Subscale of the Psychogeriatric Dependency Rating Scale.
Design: The subjects were followed up longitudinally for approximately one decade. Medical histories were taken and physical and neurologic examinations and neuropsychological testing were performed every 6 months. Three and a half years of data were available for most tests and 5.5 for the Psychogeriatric Dependency Rating Scale; thereafter, patients were no longer testable. A general linear model analysis of variance was used to assess the influence of ApoE on demographic characteristics and baseline performances on neuropsychological measures. A random-effects regression model was used to predict change over time associated with presence of epsilon 4 on clinical and cognitive measures.
Results: The age at onset was greatest for the epsilon 4-heterozygous subjects and least for the epsilon 4-negative subjects. The heterozygous subjects declined more rapidly on the Mini-Mental State Examination and the Category Fluency Test than the subjects without the epsilon 4 allele or with epsilon homozygosity. The homozygous subjects declined faster on only one subscale: the Physical Capacity subscale of the Psychogeriatric Dependency Rating Scale. Covarying for age at onset did not affect the results.
Conclusions: The ApoE genotype does not strongly influence the rate of decline in AD, implying that epsilon 4 might predispose to the development of the disease without accelerating its pathogenesis or progression. The effects of epsilon 4 on both age at onset and rate of decline need to be further investigated.