Objective: To determine whether differences in genetic origin affect the clinical course of Alzheimer's disease (AD). The limited number of cases of AD linked to a known genetic abnormality is a major obstacle in determining whether the disorder is expressed differently in patients with familial AD and those with sporadic AD.
Design: Cross-sectional study.
Setting: Memory Disorders Unit of the Alzheimer's Disease Research Center at Massachusetts General Hospital, Boston.
Participants: A total of 186 patients who had a clinical diagnosis of probable AD, family history information available for all first-degree relatives, and three or more outpatient visits were identified from a consecutive case series.
Main outcome measures: Rate of decline on the Blessed Dementia Scale and the Activities of Daily Living Scale.
Results: We calculated the probability that an individual patient has a major genetic locus for AD (MGAD) using an algorithm that incorporates information from a genetic model and the individual's family. We measured cognitive and functional changes by the average annual rate of increase (slope) in scores for the Blessed Dementia Scale and Activities of Daily Living Scale, respectively. Multivariate analysis adjusted for age at onset, duration of illness at entry into the study, and education level indicated that scores on the Activities of Daily Living Scale worsened significantly faster in men with MGAD than in men with non-MGAD. No differences in Activities of Daily Living Scale slopes were observed among women with MGAD and non-MGAD. The slopes for Blessed Dementia Scale scores were similar in men and women regardless of the MGAD probability.
Conclusions: Genetic factors may account for heterogeneity in rates of functional decline in AD. This study also illustrates the practical application of a probabilistic method that characterizes the genetic status of AD in an individual patient.