A relationship between decreased propositional density (p-density) in young adulthood and future risk for Alzheimer's disease (AD) has been postulated, but multiple interpretations of the nature of this relationship are possible. This study explored the relationship between familial AD (FAD) mutation status, apolipoprotein E (APOE) genotype, and p-density.
Thirty-five non-demented persons at risk for FAD mutations were recruited. Subjects wrote brief biographical essays from which p-density, the ratio of the number of unique ideas to the number of words in the text, was calculated. Mixed-effects regression models were used to examine the relationship of p-density and FAD mutation status and APOE genotype.
FAD mutation status was not significantly associated with p-density. However, results from both models indicated that the presence of the APOE 4 allele was significantly associated with p-density (p < 0.0001), with APOE 4 carriers having lower p-density than non-carriers.
Our results are consistent with an influence of APOE status on p-density in young adulthood that is independent of the AD risk per se and suggest the previous finding of increased risk for the development of AD in persons with decreased p-density may be related to APOE genotype.
Key Words: Presenilin 1, Amyloid precursor protein, Early-onset Alzheimer's disease, Preclinical dementia, Alzheimer's disease, Linguistic ability