Age at disease onset and pattern of cognitive impairment in probable Alzheimer's disease.

Factor analysis of cognitive scores from 150 patients with Alzheimer's disease yielded two orthogonal factors: one (Factor 1) loading high on spontaneous speech, repetition, comprehension, reading, writing, digit span, and left/right discrimination; the other (Factor 2) loading high on long-term memory, orientation, object naming, and abstraction. Regression analysis, controlled for education and disease duration, showed Factor 1 scores to be lower in early-onset patients and Factor 2 scores to be lower in late-onset patients. These data corroborate results reported by previous investigators and suggest that Alzheimer's disease is age-dependent and heterogeneous in nature.